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A comparative study of the performance of liquid chromatography (LC)–atmospheric pressure chemical ionisation (APCI)–mass spectrometry (MS) and gas chromatography (GC)–mass spectrometry techniques for the determination of resin and fatty acids from paper mill process waters was carried out. These compounds are responsible for the high toxicity of paper mill effluents and little research has been carried out regarding their analysis using mass spectrometric techniques. To prove the usability of GC and LC–MS, 16 treated and untreated water samples of recycle, kraft and pulp paper mills were analysed and good agreement was observed as regards to compounds detected and corresponding concentrations. This paper also reports the limits of detection, recoveries, reproducibility, linearity and precision using the two methods. GC–MS presented better selectivity and lower detection limits (below 0.2 μg/l), but derivatization of the extracts and the short life of derivatives (12–24 h) made the technique tedious and prone to high variations. Although LC–APCI–MS presented coelution of the non-aromatic resin acids, it also showed good sensitivity (limits of detection <3 μg/l) and permitted the detection of resin and fatty acids at μg/l level. In addition, since samples could be directly injected to the chromatographic system, LC–APCI–MS was proven as a powerful technique for quick and unequivocal quality control during papermaking. [Copyright &y& Elsevier]

Abstract: The determination of perfluorooctanoate (PFO) in articles of commerce has become increasingly important to understand if treated products are a possible source of PFO. An LC–MS/MS method for the determination of PFO in paper and textile using a dual labeled 13C-PFOA internal standard was successfully developed and validated. Residues of PFO were determined using an isocratic, reversed-phase high-performance liquid chromatography (HPLC) method with an ammonium acetate/methanol buffer. Ions monitored were 413 (parent) and 369 (daughter) for PFO and 415 (parent) and 370 (daughter) for dual labeled 13C-PFOA internal standard. As a precaution against ubiquitous PFO that occasionally occurs in mobile phase or instrument components, two Hypercarb™ cartridges (4mm) were placed before the HPLC injector. Any PFO that was captured by the cartridges was removed before each injection by flushing the system with 100% methanol prior to equilibration with the isocratic mobile phase. Overall recovery and standard deviation over a 3 day validation regimen for samples (n =54–55) fortified with PFOA at 5, 50, and 200ngg−1 were 114±4.9% for textile and 110±7.6% for paper. The results also established a limit of detection (LOD) of 1ngg−1 in textile and 2ngg−1 in paper based upon S/N of the 5.0ngg−1 fortification versus the untreated paper and textile. [Copyright &y& Elsevier]

Abstract: Lactic acidemia is commonly associated with severe diseases in pediatric patients. Quantitation of blood lactate and pyruvate is important for the diagnosis and clinical management. A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method using dried blood spots (DBS) was developed and could be used for simultaneous quantification of blood lactate and pyruvate. The applicability of the developed method was tested and confirmed by the regression analysis between LC–MS/MS method and enzymatic assay. Lactate and pyruvate were extracted from DBS obtained from 580 full-term, 120 pre-term infants (gestations ranging from 24 to 36 weeks), and 65 patients with suspected lactic acidemia, with methanolic internal standard (IS) solutions of sodium l-lactate-13C3 and pyruvate-13C3. An API-2000 LC–MS/MS system with multiple reaction monitoring (MRM) mode was applied. The within-run and between-run precisions (CV%) were determined and the results were 1.9% and 3.9% for lactate (n =20) and 5.7% and 7.3% for pyruvate (n =20). The linearity of lactate (r =0.9986) and pyruvate (r =0.9973) based on the IS was excellent. The parameter r squared (r 2) of linear regression between LC–MS/MS method and enzymatic assay was 0.9405 for lactate and 0.9447 for pyruvate, respectively, and the agreement between these methods was consistent and acceptable. The stability of lactate and pyruvate on DBS was also confirmed. The LC–MS/MS method we developed is a specific, sensitive, and reproducible method for measuring blood lactate and pyruvate concentrations. The use of DBS in this method makes it particularly attractive for pediatric patients. [Copyright &y& Elsevier]

Abstract: A method has been developed for the determination of 24 household high production volume (HPV) chemicals in municipal wastewater systems using solid-phase extraction (SPE) and analyses using both gas chromatography and liquid chromatography, each with tandem mass spectrometry (GC–MS/MS and LC–MS/MS). Target compounds include pesticides, antioxidants, fragrances, plasticizers, preservatives and personal care products. Method reporting limits ranged from 0.1 to 100ng/L in water and recoveries for most compounds were between 54 and 112%. Household HPVs were consistently detected in raw sewage entering three full-scale wastewater treatment plants. Compounds such as vanillin, DEET, benzophenone, 3-indolebutyric acid, bisphenol A, triclosan and triclocarban were detected in all wastewater influent and effluent samples, but were significantly lower in the effluent. Many of the remaining compounds were detected in the influent, but below detection in effluent samples. Menthol and phenoxyethanol had the highest observed concentrations in influent samples ranging from 1.5 to 13μg/L for menthol, and 8.8 to 22μg/L for phenoxyethanol. MGK-11, methylresorcinol, trifluralin, hexabromododecane, acriflavin and atrazine were not detected in any samples. The method described here detects a broad range of HPV chemicals with great sensitivity and selectivity. [Copyright &y& Elsevier]

• An alternative elution mode to conventional HPLC to separate compounds by class. • Sequential elution was utilized to separate classes of compounds in under 15 min. • A tandem-column stationary phase combination (SAX and C18) was utilized. • SAX+C18 and C18+SAX column orientations yielded nearly identical separations. • Retention time and peak area precision were below 1.5 % RSD. This paper discusses the development of an analytical method by an alternative separation approach, sequential elution liquid chromatography (SE-LC), to separate permanently charged ions (anions), weak acids, and neutral compounds using anion exchange and reversed-phase columns in tandem. SE-LC separates classes of compounds by group by employing two or more elution modes. Advantages to using SE-LC over conventional HPLC are a greater peak capacity and a reduced separation disorder. Importantly, the same HPLC as used for a conventional HPLC separation may be used to afford a successful SE-LC separation. Mobile phase selection and gradient optimization are integral for a successful SE-LC class separation of permanent anions, weak acids, and neutral compounds and will be discussed in detail in this paper. The most successful (best resolution and repeatability) SE-LC separation was achieved by applying isocratic elution at low pH to elute the weak acids, followed by an acetonitrile gradient to elute the neutral compounds, and last a sodium methanesulfonate gradient to elute the anionic compounds using a superficially porous C18 column coupled with a strong anion exchange (SAX) column. Repeatability (RSD) in the retention times and peak areas of the analytes was less than 0.25 % and 1.5 %, respectively. [ABSTRACT FROM AUTHOR]

• A data-driven model for reversed phase selectivity is established. • A revised hydrophobic subtraction model is proposed. • Accurate predictions of isomer selectivity are made. Reversed-phase (RP) liquid chromatography is an important tool for the characterization of materials and products in the pharmaceutical industry. Method development is still challenging in this application space, particularly when dealing with closely-related compounds. Models of chromatographic selectivity are useful for predicting which columns out of the hundreds that are available are likely to have very similar, or different, selectivity for the application at hand. The hydrophobic subtraction model (HSM1) has been widely employed for this purpose; the column database for this model currently stands at 750 columns. In previous work we explored a refinement of the original HSM1 (HSM2) and found that increasing the size of the dataset used to train the model dramatically reduced the number of gross errors in predictions of selectivity made using the model. In this paper we describe further work in this direction (HSM3), this time based on a much larger solute set (1014 solute/stationary phase combinations) containing selectivities for compounds covering a broader range of physicochemical properties compared to HSM1. The molecular weight range was doubled, and the range of the logarithm of the octanol/water partition coefficients was increased slightly. The number of active pharmaceutical ingredients and related synthetic intermediates and impurities was increased from four to 28, and ten pairs of closely related structures (e.g., geometric and cis -/ trans - isomers) were included. The HSM3 model is based on retention measurements for 75 compounds using 13 RP stationary phases and a mobile phase of 40/60 acetonitrile/25 mM ammonium formate buffer at pH 3.2. This data-driven model produced predictions of ln α (chromatographic selectivity using ethylbenzene as the reference compound) with average absolute errors of approximately 0.033, which corresponds to errors in α of about 3 %. In some cases, the prediction of the trans -/ cis - selectivities for positional and geometric isomers was relatively accurate, and the driving forces for the observed selectivity could be inferred by examination of the relative magnitudes of the terms in the HSM3 model. For some geometric isomer pairs the interactions mainly responsible for the observed selectivities could not be rationalized due to large uncertainties for particular terms in the model. This suggests that more work is needed in the future to explore other HSM-type models and continue expanding the training dataset in order to continue improving the predictive accuracy of these models. Additionally, we release with this paper a much larger data set (43,329 total retention measurements) at multiple mobile phase compositions, to enable other researchers to pursue their own lines of inquiry related to RP selectivity. [ABSTRACT FROM AUTHOR]

• Dimethyl carbonate is tested as green alternative to acetonitrile. • Dimethyl carbonate is slightly soluble in water, but it has high elution strength. • Dimethyl carbonate and acetonitrile showed comparable kinetic performance. Nowadays, environmental problems are drawing the attention of governments and international organisations, which are therefore encouraging the transition to green industrial processes and approaches. In this context, chemists can help indicate a suitable direction. Beside the efforts focused on greening synthetic approaches, currently also analytical techniques and separations are under observation, especially those employing large volumes of organic solvents, such as reversed-phase liquid chromatography (RPLC). Acetonitrile has always been considered the best performing organic modifier for RPLC applications, due to its chemical features (complete miscibility in water, UV transparency, low viscosity etc); nevertheless, it suffers of severe shortcomings, and most importantly, it does not fully comply with Environmental, Health and Safety (EHS) requirements. For these reasons, alternative greener solvents are being investigated, especially easily available alcohols. In this work, chromatographic performance of the most common solvents used in reversed-phase chromatography, i.e., acetonitrile, ethanol and isopropanol, have been compared to a scarcely used solvent, dimethyl carbonate (DMC). The analytes of interest were two small molecules, caffeine and paracetamol, whose kinetics and retention behaviour obtained with the four solvents have been compared, and all contributions to band broadening have been assessed. Results about kinetic performance are very promising, indicating that a small amount (7 % v/v) of DMC is able to produce the same efficiency as a 2.5-times larger ACN volume (18 % v/v), and larger efficiency than alcohols. This paper reports, for the first time, fundamental studies concerning the mass transfer phenomena when DMC is used as an organic solvent in RPLC, and, together with the companion paper, represents the results of a research whose final aim was to discover whether DMC is suitable for chromatographic applications both in linear and preparative conditions. [ABSTRACT FROM AUTHOR]

• The impact of lateral flow induced by AC electroosmotic flow on Taylor dispersion was studied in rectangular micro-channels with critical dimension of 3 µm. • Generalized dispersion theory was used to evaluate and predict Taylor dispersion with wall retention. • The influence of aspect ratio, retention, diffusion coefficient and potential was studied. Axial dispersion in chromatographic columns is responsible for a reduced separation efficiency. In the present research macrotransport theory is used to predict the phenomenological constants related to axial dispersion. We evaluate the efficacy of lateral flow induced by alternating current (AC) in the presence of retaining walls on the separation resolution. Results show that lateral flows induced by laterally applied potentials as low as 0.3 V reduce C-term dispersion by a factor of 5.0 for unretained conditions (k = 0) and 2.7 for retained (k = 5) conditions, with a diffusion coefficient (D m) of 10–11m2/s. The present paper further contributes to the understanding of the use of secondary lateral flows for dispersion reduction and offers practical guidance for designing future vortex chromatographic columns. It appears that a maximal performance gain is attained at low aspect ratios (AR=1), with the gain reduced from a factor of 5 to 1.6 for AR=4 for unretained conditions, and from 2.7 to 1.4 for retained conditions (k = 5) [ABSTRACT FROM AUTHOR]

• Looking for a gradient profile to determine primary aromatic amines with HPLC-FLD. • In-house program written in MATLAB to set up a gradient profile for the mobile phase. • Exploration of a ternary mixture diagram by means of PLS models and a few experiments. • Four critical quality attributes in chromatography are fitted by means of PLS models. • Aniline and 2,4-diaminotoluene found in paper napkins made with recycled fibres. The purpose of this work is to develop a tool to search for a gradient profile with ternary or binary mixtures in liquid chromatography, that can provide well-resolved chromatograms in the shortest time for multianalyte analysis. This approach is based exclusively on experimental data and does not require a retention time model of the compounds to be separated. The methodology has been applied for the quantification of four primary aromatic amines (PAAs) using HPLC with fluorescence detector (FLD). Aniline (ANL), 2,4-diaminotoluene (TDA), 4,4′-methylenedianiline (MDA) and 2-aminobiphenyl (ABP) have been selected since their importance in food contact materials (FCM). In order to achieve that, partial least squares (PLS) models have been fitted to relate CMP (control method parameters) and CQA (critical quality attributes). Specifically, PLS models have been fitted using 30 experiments for each one of the four CQA (resolution between peaks and total elution time), considering 33 predictor variables (the composition of the methanol and acetonitrile in the mobile phase and the time of each one of the 11 isocratic segments of the gradient). These models have been used to predict new candidate gradients, and then, some of those predictions (the ones with resolutions above 1.5, in absolute value, and final time lower than 20 min) have been experimentally validated. Detection capability of the method has been evaluated obtaining 1.8, 189.4, 28.8 and 3.0 µg L−1 for ANL, TDA, MDA and ABP, respectively. Finally, the application of chemometric tools like PARAFAC2 allowed the accurate quantification of ANL, TDA, MDA and ABP in paper napkins in the presence of other interfering substances coextracted in the sample preparation process. ANL has been detected in the three napkins analysed in quantities between 33.5 and 619.3 µg L−1, while TDA is present in only two napkins in quantities between 725.9 and 1908 µg L−1. In every case, the amount of PAAs found, exceeded the migration limits established in European regulations. [ABSTRACT FROM AUTHOR]

• A LC system was constructed with a miniaturized photometric detector and a microfluidic chip. • The Z-shaped cell design increases the effective optical path length. • The Z-shaped cell and column are on the same chip without a pipeline connection. • The microchip can be filled with cation exchange resin and C18 particles. In recent years, miniaturized analytical instruments have been developing to meet the needs of portable and rapid analysis. The key of miniaturized analytical equipment is the miniaturization and integration of functional modules. This paper aims to develop a miniaturized photometric detector and separation microfluidic chip for a liquid chromatography (LC) system. The detector uses a light-emitting diode to emit ultraviolet light, which is collimated by an internal double lens. A Z-shaped flow cell with a long optical path is designed and fabricated in the separation microfluidic chip with a three-layer structure, which provides a tubing-free connection between the separation and detection unit. Detector performance is evaluated using hemoglobin (Hb) samples, with an upper limit of detection linearity (95 %) of 0.345 AU and stray light level as low as 0.08 %. Additionally, the microchip channel can be filled with cation exchange resin and C18 particles. Finally, an ion LC system and a reversed-phase LC system were constructed based on the miniaturized photometric detector and two microchips with different packed columns, respectively, and were successfully used in the separation and detection of two metabolic markers (glycated hemoglobin or bilirubin). The results of this study are expected to facilitate the development of a portable LC system and their application in community health services and family health management of chronic diseases. [ABSTRACT FROM AUTHOR]

• The in situ growth method was employed to prepare COF-TpPa-1@SiO 2 microspheres. • The microspheres can be used as RP/HILIC mixed-mode stationary phase. • The stationary phase exhibited excellent resolution in separating small solutes. • The stationary phase can enhance the aromatic, shape and planar selectivity. Covalent organic frameworks (COFs) show promise as a stationary phase in high performance liquid chromatography (HPLC). However, there are only a few COFs-based stationary phases developed for HPLC separation so far. Therefore, it is crucial to not only develop more varieties of COFs-type stationary phases for HPLC separation, but also to explore the retention mechanism of solutes on these stationary phases. In this paper, a new in-situ growth method was developed to prepare β -ketoenamine COF-TpPa-1@SiO 2 composite microspheres, using spherical silica as the core material and COF-TpPa-1 fabricated by covalent conjugation of 1,3,5-triformylphloroglucinol (Tp) and p -phenylenediamine (Pa-1) as the COF shells. The resulting microspheres exhibit uniform morphology, good monodispersity, large specific surface area, narrow size distribution, and high stability. Due to diverse functional groups in the structure of COF-TpPa-1, the microspheres can offer multiple interactions, such as hydrophobic, π-π stacking and electron-donor–acceptor (EDA) between COFs and analytes. As a result, the COF-TpPa-1@SiO 2 composite microspheres can be used as a mixed-mode stationary phase for HPLC separation. The chromatographic performance and retention mechanism of the COF-TpPa-1@SiO 2 packed column were investigated by separating polar and non-polar solutes, as well as isomers, in various HPLC modes, including reversed-phase liquid chromatography (RPLC), hydrophilic interaction chromatography (HILIC), and RPLC/HILIC mixed-mode chromatography. The results showed successful separation of non-polar alkylbenzene homologues, polycyclic aromatic hydrocarbons (PAHs), and polar amines and phenols in RPLC mode. The "U-shaped" curves of retention factor with the ACN concentration in mobile phase for four nucleobases indicated that the solute retention on the column followed a mixed mode mechanism of RPLC/HILIC. Compared to a traditional C18 column, the COF-TpPa-1@SiO 2 column exhibited superior separation efficiency, stability, repeatability and reproducibility in the separation of analytes with different polarities. The column enhanced the aromatic, shape and planar selectivity for PAHs and isomers through π-π interaction and improved the separation efficiency for electron-deficient compounds due to EDA effect. At last, the column was successfully used to separate and detect the residues of 5 phenylurea herbicides (PUHs) in soil. All these results indicate the potential of COFs for chromatography applications. [ABSTRACT FROM AUTHOR]

• Rapid, direct injection LC/MS-QTOF method for resin acids without derivatization. • MDL in range 0.05 to 0.07 µgL−1 for six resin acids in aqueous alkaline matrix. • Precision and accuracy from 1 µgL−1 to 40 µgL−1 in matrix. • Isopimaric as calibrant for six C 20 H 30 O 2 resin acids. • Transferred to LC/MS/MS and successfully applied to environmental samples. A rapid and sensitive liquid chromatography (LC) quadrupole time of flight (QTOF) method has been developed for the determination of resin acid concentrations in aqueous pulp and paper effluent related samples. Calibration R2 of ≥0.995 for twelve resin acids, namely dehydroabietic, 8(14)-abietenic, dihydroisopimaric, levopimaric, neoabietic, pimaric, sandaracopimaric, abietic, isopimaric, palustric, chlorodehydroabietic, and dichlorodehydroabietic acids, was demonstrated in the range 1 µgL−1 to 40 µgL−1. An improved lower limit of quantitation was achieved without use of complex sample extraction and clean-up procedures undertaken by other published methods. Excellent precision and accuracy results were achieved for dehydroabietic, chlorodehydroabietic, dichlorodehydroabietic, isopimaric (integrated inclusive of all C 20 H 30 O 2 resin acids), dihydroisopimaric and 8(14)-abietenic resin acids, with t-99 percentile detection limits spanning the range 0.05 to 0.07 µgL−1. While measurement for the C 20 H 30 O 2 resin acids by isopimaric equivalence is considered semi-quantitative and could be an under estimate for the abietic acid component, the developed method demonstrated clear advantage over time consuming, hazardous, and unstable derivatization procedures used for gas chromatography and capillary electrophoresis. The developed LC/QToF method was successfully transferred to an LC triple quadrupole mass spectrometer for routine high throughput trace level analysis. Real world samples, including sea water and estuary water, demonstrated excellent spike recoveries by this procedure, indicating that the method is well suited to the monitoring of industrially derived resin acids in environmental surface waters. While no interferences were observed during routine sample analysis using myristic-1-13C acid and palmitic-1-13C acid internal standards, these were later substituted by myristic-d 27 and palmitic-d 31 acid in order to improve method robustness for environmental samples where endogenous parent fatty acids could be present. [ABSTRACT FROM AUTHOR]

This paper details the use of a method of creating controlled pH gradients (pISep) to improve the separation of protein isoforms on ion exchange (IEX) stationary phases in the presence of various isocratic levels of urea. The pISep technology enables the development of computer controlled pH gradients on both cationic (CEX) and anionic (AEX) IEX stationary phases over the very wide pH range from 2 to 12. In pISep, titration curves generated by proportional mixing of the acidic and basic pISep working buffers alone, or in the presence of non-buffering solutes such as the neutral salt NaCl (0–1 M), polar organics such as urea (0–8 M) or acetonitrile (0–80 Vol%), can be fitted with high fidelity using high order polynomials which, in turn allows construction of a mathematical manifold %A (% acidic pISep buffer) vs. pH vs. [non-buffering solute], permitting precise computer control of pH and the non-buffering solute concentration allowing formation of dual uncoupled liquid chromatographic (LC) gradients of arbitrary shape (Hirsh and Tsonev, 2012 [1] ). The separation of protein isoforms examined in this paper by use of such pH gradients in the presence of urea demonstrates the fractionation power of a true single step two dimensional liquid chromatography which we denote as Stability-Influenced Ion Exchange Chromatography (SIIEX). We present evidence that SIIEX is capable of increasing the resolution of protein isoforms difficult to separate by ordinary pH gradient IEX, and potentially simplifying the development of laboratory and production purification strategies involving on-column simultaneous pH and urea unfolding or refolding of targeted proteins. We model some of the physics implied by the dynamics of the observed protein fractionations as a function of both urea concentration and pH assuming that urea-induced native state unfolding competes with native state electrostatic interaction binding to an IEX stationary phase. Implications for in vivo protein-membrane interactions are discussed. [ABSTRACT FROM AUTHOR]

This paper presents the state of the art concerning the separation of chiral compounds by means of nano-liquid chromatography (nano-LC). The enantiomers’ separation and determination are a subject of fundamental importance in various application fields such as pharmaceutical industry, biomedicine, food, agrochemical etc. Nano-LC is a miniaturized chromatographic technique offering some advantages over conventional ones such as low consumption of mobile phase, sample volume and amount of chiral stationary phase, reduced costs etc. This is reported in the first part of the paper illustrating the features of the nano-LC. In addition, chiral resolution methods are briefly illustrated. Some chiral selectors, used in high-performance liquid chromatography have also been applied in nano-LC including cyclodextrins, glycopeptide antibiotics, modified polysaccharides etc. This is discussed in the second part of the review. Finally some examples of the applications available in literature are reported. [ABSTRACT FROM AUTHOR]

• Two-dimensional separations enable peak purity analysis of pharmaceutical peptides. • Strategy to derive second-dimension gradient conditions. • Preferred gradient conditions discovered by retention modelling. The importance of therapeutic peptides continues to increase in the marketplace for treating a range of diseases including diabetes and obesity. Quality control analyses for these pharmaceutical ingredients usually depends on reversed-phase liquid chromatography, and it is critically important to ensure that no impurities coelute with the target peptide at levels that would compromise the safety or effectiveness of the drug products. This can be challenging due to the broad range of properties of impurities that can be present on one hand (e.g., amino acid substitutions, chain cleavages, etc.), and the similarity of other impurities on the other hand (e.g., d -/ l -isomers). Two-dimensional liquid chromatography (2D-LC) is a powerful analytical tool that is well suited to address this particular problem; the first dimension can be used to detect impurities over a broad range in properties, while the second dimension can be used to focus specifically on those species that might coelute with the target peptide in the first dimension. While hundreds of papers have been published on the use of 2D-LC for proteomics applications, there are very few papers that have focused on its use for characterisation of therapeutic peptides. This paper is the second in a two-part series. In Part I of the series, we studied several different column / mobile phase combinations that could be useful in 2D-LC separations of therapeutic peptides, with a focus on selectivity, peak shape, and complementarity to other combinations, particularly for isomeric peptides under mass spectrometry-friendly conditions (i.e., volatile buffers). In this second part in the series, we describe a strategy to derive second-dimension (2D) gradient conditions that both, ensure elution from the 2D column, and increase the likelihood of resolving peptides with very similar properties. We find that a two-step process yields conditions that place the target peptide in the middle of the 2D chromatogram. This process begins with two scouting gradient elution conditions in the second dimension of a 2D-LC system, followed by building and refining a retention model for the target peptide using a third separation. The process is shown to be generically useful by developing methods for four model peptides, and application to a sample of degraded model peptide to demonstrate its utility for resolving impurities in a real sample. [ABSTRACT FROM AUTHOR]

• Three imidazole- and C18- bifunctional silica stationary phases (Sil-Im-C18) were prepared. • Chromatographic performance can be adjusted by the control of different co-grafting amounts of C18 chain and imidazole group. • The prepared stationary phases can be used in reversed-phase liquid chromatography (RPLC) and ion exchange chromatography (IEC). • Excellent separation performance for PAHs, phenylesters, phenylamines, phenols and inorganic anions was obtained. • Nucleobases and nucleosides can be separated using pure water as mobile phases. In this paper, three imidazole- and C18- bifunctional silica stationary phases (Sil-Im-C18) were prepared by adjusting introduction interval of octadecyltrichlorosilane (ODS) and 3-imidazol-1-ylpropyl(trimethoxy)silane (TMPImS), which can be used for reversed-phase liquid chromatography (RPLC) and ion exchange chromatography (IEC) with adjustable performance. The successful preparation of Sil-Im-C18 were confirmed by the characterizations of elemental analysis, infrared spectroscopy (FTIR) and contact angle (CA). Chromatographic performance of Sil-Im-C18 were evaluated by the separation of Tanaka test mixture, alkylbenzenes, linear PAHs and a set of analytes with different properties (uracil, phenol, 1,2-dinitrobenzene and naphthalene), and compared with commonly used C18 column. It was found that the chromatographic performance of Sil-Im-C18 changed significantly with the difference in bonding amount of imidazole and C18. Sil-Im-C18 demonstrated the excellent separation performance towards polycyclic aromatic hydrocarbons (PAHs), phenylesters, phenylamines, phenols and inorganic anions, and notably, nucleobases and nucleosides can be separated using pure water as mobile phases. The van Deemter plot showed that the column efficiency of Sil-Im-C18-3 was 64,933 plate· m −1 for naphthalene, indicated that Sil-Im-C18 was reasonably chromatographic columns. The RSD values of retention time were 0.22 %-0.61 % for 10 needles alkylbenzenes injected continuously at 50 °C to investigate thermal stability and repeatability, all the fluctuations of k of naphthalene were less than 2.3 % for Sil-Im-C18-1 during flushing 24 h with the mobile phase at different pH values (pH = 3 and 8), the retention time of alkylbenzenes were almost same for Sil-Im-C18-1 at different time, the RSD values of retention time of alkylbenzenes were 0.45 %-2.28 % for two batches Sil-Im-C18-1, revealing the excellent repeatability, thermal stability, durability and reproducibility of Sil-Im-C18, and implying a commercial prospect. [ABSTRACT FROM AUTHOR]

While Reinforcement Learning (RL) has already proven successful in performing complex tasks, such as controlling large-scale epidemics, mitigating influenza and playing computer games beyond expert level, it is currently largely unexplored in the field of separation sciences. This paper therefore aims to introduce RL, specifically proximal policy optimization (PPO), in liquid chromatography, and evaluate whether it can be trained to optimize separations directly, based solely on the outcome of a single generic separation as input, and a reward signal based on the resolution between peak pairs (taking a value between [ − 1 , 1 ]). More specifically, PPO algorithms or agents were trained to select linear (1-segment) or multi-segment (2-, 3-, or 16-segment) gradients in 1 experiment, based on the outcome of an initial, generic linear gradient (ϕ s t a r t = 0.3 , ϕ e n d = 1.0 , and t g = 20 min), to improve separations. The size of the mixtures to be separated varied between 10 and 20 components. Furthermore, two agents, selecting 16-segment gradients, were trained to perform this optimization using either 2 or 3 experiments, in sequence, to investigate whether the agents could improve separations further, based on previous outcomes. Results showed that the PPO agent can improve separations given the outcome of one generic scouting run as input, by selecting ϕ -programs tailored to the mixture under consideration. Allowing agents more freedom in selecting multi-segment gradients increased the reward from 0.891 to 0.908 on average; and allowing the agents to perform an additional experiment increased the reward from 0.908 to 0.918 on average. Finally, the agent outperformed random experiments as well as standard experiments (ϕ s t a r t = 0.0 , ϕ e n d = 1.0 , and t g = 20 min) significantly; as random experiments resulted in average rewards between 0.220 and 0.283, and standard experiments resulted in average rewards of 0.840. In conclusion, while there is room for improvement, the results demonstrate the potential of RL in chromatography and present an interesting future direction for the automated optimization of separations. • Proximal policy optimization (PPO) for the direct optimization of separations. • PPO agent learned to select multi-step gradients to optimize separations of mixtures. • PPO agent improved separations based on the outcome of initial linear gradients. [ABSTRACT FROM AUTHOR]

• Introducing modeling methodology for a robust assessment of UHPLC column provided selectivities. • Multidimensional Design Spaces offering AQbD-compliant alternative for column selectivity testing and comparison methods. • Identifying shared method conditions with established interchangeability between various C18 stationary phases. • Pharmaceutical application: optimal workpoints, substitute columns, ensure consistency, identification of equivalent/orthogonal column selectivities. Current guides and column selection system (CSS) platforms can provide some helpful insights with regard to the selection of alternative phases. Their practical reliability however, can also turn out to be questionable, especially considering the lack of detailed specifics, such as a clear definition of points of equivalence—appropriate running conditions under which the given analytical mixture can be satisfactorily resolved on various stationary phases. In this context, the use of multivariate modeling tools can be highly beneficial. These tools, when applied systematically, are ideal for uniquely characterizing complex LC-separation systems, a fact supported by numerous peer-reviewed papers. Revisiting our earlier work [1] and the applied systematic workflow [2] , we used a Design Space modeling software (DryLab), with the main focus on building and comparing 3-dimensional separation models of amlodipine and its related impurities to identify shared method conditions under which columns are conveniently interchangeable. Our study comprised 5, C18-modified ultra-high performance liquid chromatography (UHPLC) columns in total, in some cases with surprising results. We identified several equivalences between the Design Spaces (DSs) of markedly different columns. Conversely, there were cases where, despite the predicted similarities in column data, the modeled DSs demonstrated clear differences between the selected stationary phases. [ABSTRACT FROM AUTHOR]

Recently, interest in supercritical fluid chromatography (SFC) has increased due to its high throughput and the development of new system improving chromatographic performances. However, most papers dealt with fundamental studies and chiral applications and only few works described validation process of SFC method. Likewise, evaporative light scattering detection (ELSD) has been widely employed in liquid chromatography but only a few recent works presented its quantitative performances hyphenated with SFC apparatus. The present paper discusses about the quantitative performances of SFC-ELSD compared to HPLC-ELSD, for the determination of plasticizers (ATBC, DEHA, DEHT and TOTM) in PVC tubing used as medical devices. After the development of HPLC-ELSD, both methods were evaluated based on the total error approach using accuracy profile. The results show that HPLC-ELSD was more precise than SFC-ELSD but lower limits of quantitation were obtained by SFC. Hence, HPLC was validated in the ±10% acceptance limits whereas SFC lacks of accuracy to quantify plasticizers. Finally, both methods were used to determine the composition of plasticized-PVC medical devices. Results demonstrated that SFC and HPLC both hyphenated with ELSD provided similar results. [ABSTRACT FROM AUTHOR]

• Dimethyl carbonate is used as organic modifier in preparative chromatography. • Dimethyl carbonate and acetonitrile lead to comparable purity values. • Solvent consumption is considerably reduced with dimethyl carbonate. Preparative liquid chromatography in reversed phase conditions (RPLC) is the most common approach adopted in the downstream processing for the purification of therapeutic peptides at industrial level. Due to the strict requirements on the quality imposed by the Regulatory Agencies, routinary methods based on the use of aqueous buffers and acetonitrile (ACN) as organic modifier are commonly used, where ACN is practically the only available choice for the purification of peptide derivatives. However, ACN is known to suffers of many shortcomings, such as drastic shortage in the market, high costs and, most importantly, it shows unwanted toxicity for human health and environment, which led it among the less environmentally friendly ones. For this reason, the selection of a suitable alternative becomes crucial for the sustainable downstream processing of peptides and biopharmaceuticals in general. In this paper, a promising green solvent, namely dimethyl carbonate (DMC) has been used for the separation of a peptide not only in linear conditions but also for its purification through non-linear overloaded chromatography. The performance of the process has been compared to that achievable with the common method where ACN is used as organic modifier and to that obtained with two additional solvents (namely ethanol and isopropanol), already used as greener alternatives to ACN. This proof-of-concept study showed that, thanks to its higher elution strength, DMC can be considered a green alternative to ACN, since it allows to reduce method duration while reaching good purities and recoveries. Indeed, at a target purity fixed to 98.5 %, DMC led to the best productivity with respect to all the other solvents tested, confirming its suitability as a sustainable alternative to ACN for the purification of complex biopharmaceutical products. [ABSTRACT FROM AUTHOR]

• Migration of chemicals from paper-based food packaging • LC-HRMS non-targeted workflow for data analysis • Improved identification using t R prediction model based on t R /log K ow relationship Potential contamination of food with chemicals migrating from food packaging is an important, yet under-investigated area of food safety. In this study, we examined chemicals migrating from common paper-based food packaging: pizza boxes and pizza box liners, butcher paper and liquid egg containers. Migration tests were conducted with a food simulant for 10 days, and migrated chemicals were identified with liquid chromatography (LC) - high resolution mass spectrometry (HRMS) with mass error < 3 ppm. HRMS identification was based on spectra and/or structure matching against commercial databases (MzCloud, ChemSpider, and Extractable and Leachable high resolution accurate mass (HRAM) database). Following HRMS identification, orthogonal LC retention information was utilized to further refine the data and reduce false positive findings. A model for calculating retention times (t R) based on octanol-water partition coefficient (log K ow) values was evaluated and applied for HRMS data refining. Using this approach, 153 migrated chemicals were identified, of which five were further confirmed with reference analytical standards. Additionally, amounts of bisphenol A and bisphenol S, the chemicals of toxicological concerns, were measured at the levels below the established regulatory limits for migration, indicating no/low risk to consumer's health. This study demonstrated the utility of LC-HRMS for confident identification of food packaging migrants. [ABSTRACT FROM AUTHOR]

Abstract: The recent introduction of new stationary phases for liquid chromatography based on superficially porous particles, called core–shell or fused-core, dramatically improved the separation performances through very high efficiency, due mainly to reduced eddy diffusion. However, few studies have evaluated the retention and selectivity of C18 phases based on such particles, despite some retention order change reported in literature between some of these phases. The carotenoid test has been developed a few years ago in the goal to compare the chromatographic properties of C18 bonded phases. Based on the analysis of carotenoid pigments by using Supercritical Fluid Chromatography (SFC), it allows, with a single analysis, to measure three main properties of reversed phase chromatography stationary phases: hydrophobicity, polar surface activity and shape selectivity. Previous studies showed the effect of the endcapping treatment, the bonding density, the pore size, and the type of bonding (monomeric vs. polymeric) on these studied properties, and described the classification map used for a direct column comparison. It was applied to ten ODS superficially porous stationary phases, showing varied chromatographic behaviors amongst these phases. As expected, due to the lower specific surface area, these superficially porous phases are less hydrophobic than the fully porous one. In regards of the polar surface activity (residual silanols) and to the shape selectivity, some of these superficially porous phases display close chromatographic properties (Poroshell 120, Halo C18, Ascentis Express, Accucore C18, Nucleoshell C18 on one side and Aeris Wide pore, Aeris peptide and Kinetex XDB on the other side), whereas others, Kinetex C18 and Halo peptide ES C18 display more specific ones. Besides, they can be compared to classical fully porous phases, in the goal to improve method transfer from fully to superficially porous particles. By the way, the paper also report the extension of the test to other ligands such as naphtyl, cholester, phenyl-hexyl, or to the new ODS bonded phases, such as charge surface hybrid phases, High Strength Silica, and Hybrid ones, and also presents results for identical brands using different particle size, such as Luna and Synergi phases. Phenyl-hexyl and napthyl ligands show rather close properties, low hydrophobicity, high polar surface activity and specific shape selectivity, whereas, at the opposite, the cholester phase display a polymeric behavior and a high hydrophobicity. Finally, additional classical (fully porous particles) C18 bonded phases are also reported to complete the data set presented in previous papers. [Copyright &y& Elsevier]

Abstract: The general method for constructing coupled dual gradients in liquid chromatography (LC) is to begin by filling a reservoir A with a solution of one mobile phase (MP) component at concentration [c 1(A)] and a second MP component at concentration [c 2(A)], followed by filling a reservoir B with a solution containing MP component one at concentration [c 1(B)] and the second MP component at concentration [c 2(B)]. In another scenario the reservoirs A and B are filled with solutions of only one MP component at different concentrations [c 1(A)] and [c 1(B)] and the two solutions are titrated to a different pH value: pH (A) for the reservoir A and pH (B) for the reservoir B respectively. In either case, mixing of flows from the two reservoirs varies the concentrations of the two MP components (MP solutes) or the concentration of one MP component and pH along a particular compositional curve producing an eluent with two compositionally coupled gradients. This is a kind of a two dimensional LC utilizing dual simultaneous dependent gradients (DSDGs) wherein two parameters affecting the binding free energy of an analyte to a stationary phase (SP) are being altered simultaneously. Such a DSDG suffers from a significant limitation in that the gradient concentration of the two solutes or the concentration of one MP component and the pH cannot be varied independently. The only way to attain an optimal multigradient LC system, that promises a remarkable increase in chromatographic resolution of complex analyte mixtures, is to uncouple the multiple (dual) gradients, making each independent of the other(s). In this paper the theory of uncoupling of n such gradients, n ≥2 is developed. It is shown that for n solutes 2 n reservoirs are required in concert with an LC eluent delivery system capable of freely apportioning the flows among the reservoirs according to equations we develop here. We go on to predict a substantial increase in chromatographic resolution when applying dual simultaneous independent gradients (DSIGs) of salt and pH to fractionate difficult to separate proteins. This prediction is naturally explained by the electrostatic interaction theory of protein binding to an ion exchanger. In subsequent experimental papers it will be shown that the algorithms presented here properly instruct a quad pump HPLC system to produce well controlled independent simultaneous gradients of pH and non-buffering solutes with attendant significant gain in chromatographic resolution of complex mixtures of protein isoforms. [Copyright &y& Elsevier]

Abstract: Columns packed with sub-2μm totally porous and sub-3μm core–shell particles are very widespread nowadays to conduct fast and efficient separations. In order to carry out really fast separations, short (5cm long) columns are very popular today. The goal of this paper is to review the recent possibilities in fast or “ultra-fast” HPLC by applying short and narrow bore columns packed with modern core–shell and very fine fully porous particles. Efficiency data obtained with these recently commercialized columns from the past few years are collected, discussed and compared in terms of potential separation time and efficiency. The reasons of the success of these columns are presented. This paper also shows that theoretically expected efficiency is sometimes compromised in practical work especially in the case of narrow bore columns. The extra-column dispersion of a given LC system can also dramatically decrease the performance of small columns. It is not possible to utilize the real efficiency of these small columns in spite of their really high intrinsic separation power. [Copyright &y& Elsevier]

• Fabric phase sorptive extraction was applied for enrichment of acrylate compounds • Under the optimized condition satisfactory results were obtained • Thirteen types of recycled polyethylene terephthalate were chosen as real samples • Migration of acrylates to food simulants investigated • Acrylates were found in some samples at ng g−1 levels This article presents fabric phase sorptive extraction (FPSE) as a simple and effective pre-concentration method for the enrichment of acrylate compounds in different food simulants and subsequent analysis of the extracts by ultra-high-performance liquid chromatography with mass spectrometric detection (UPLC-MS). Acrylate compounds come from acrylic adhesives used commonly for sticking the paper labels on polyethylene terephthalate (PET) bottles and therefore, they may exist in recycled polyethylene terephthalate (rPET). Four acrylates were studied: ethylene glycol dimethacrylate (EGDM), pentaerythritol triacrylate (PETA), triethylene glycol diacrylate (TEGDA) and trimethylolpropane triacrylate (TMPTA). Five different types of FPSE media coated with different sol-gel sorbents were studied and finally sol-gel polyethylene glycol- polypropylene glycol-polyethylene glycol triblock copolymer (PEG-PPG-PEG) coated FPSE media was chosen for its satisfactory results. The optimal conditions affecting the extraction efficiency of compounds were determined in three different food simulants. Statistical evaluation of this method reveals good linearity and precision. Under the optimized conditions, the method provided limits of detection of the compounds in the range of (0.1–1.9 ng g−1, 0.1–1.2 ng g−1, 0.2–2.3 ng g−1) in EtOH 10%, HAc 3% and EtOH 20% and the enrichment factor values (EFs) after applying N 2 were in the range of 11.1–25.0, 13.8–26.3, 8.3–21.9, in simulants A, B and C respectively. The optimized method was applied successfully to analyze thirteen types of recycled PET samples. Acrylates were found in some of the samples at ng g−1 levels. [ABSTRACT FROM AUTHOR]

• Study on SFC mechanism by LSER characterization of five C8 stationary phases. • Discussion about the influence of C8 bonding density on SFC selectivity. • Complementarity of five C8 stationary phases proved by the vector angle. • H-bonding interaction can be greatly affected by the modifier's type and proportion. Supercritical fluid chromatography (SFC) today represents an alternative technique in analytical chemistry due to its obvious benefits in kinetic performance and its complementarity to liquid chromatography. In this paper, a series of alkylsiloxane-bonded stationary phases were synthesized and evaluated to expand their SFC applications. Five kinds of non-endcapped C8 stationary phases (C8-1 to C8-5) with increasing bonding density were synthesized, and the carbon content was 3.91%, 6.07%, 7.97%, 8.65% and 9.10% respectively. Retention mechanism of the C8 phases in SFC in SFC was investigated by the use of a linear solvation energy relationship (LSER) model. Results underlined a close relationship between the bonding density of alkyl chain and the dispersion and polar interactions of the stationary phase. Complementary evaluation was studied based on the calculation of vector angle (θ), and the widest θ of 123° was found between silica and C8 with the highest bonding density. Selective diversity also existed between the two C8 phases with the highest and lowest bonding densities. In addition, the effect of modifier on the SFC mechanism was investigated. Modifiers (methanol, ethanol, isopropanol and acetonitrile) had insignificant influence on the dispersion interaction but they mainly affected the hydrogen bonding interaction by changing the LSER parameters a and b. Finally, C8 and silica columns were applied for separation of eight amide alkaloids of Piper kadsura. Silica provided better retention but limited selectivity while C8 can distinguish alkaloids different in alkyl chain, double bond and cis - trans structure. This research further contributed to demonstrate the potential of alkylsiloxane-bonded stationary phase in improving selectivity of SFC. [ABSTRACT FROM AUTHOR]

Highlights • Matrix effect does not limit the use of CPE coupled to LC–MS/MS. • Low surfactant concentration and high extraction temperature reduce the risk of ME. • Significant absolute ME (<85% or >115%) was observed only for 25% of the analytes. • Molecular descriptors (HDB, ClogP, PSA) help to identify compounds prone to ME. • A new term – the surfactant effect – was introduced. Abstract Matrix effects are one of the most challenging issues in the analysis of complex samples using liquid chromatography coupled to mass spectrometry (LC–MS). Apart from the instrumental origin, these effects are also related to sample preparation. Cloud-point extraction (CPE) is rarely combined with LC–MS as it requires the use of surfactants which might interfere with droplet evaporation. Thus, they are suspected to cause a significant matrix effect (signal suppression). In this paper, 73 model drugs with different physicochemical properties were screened to analyse how susceptible LC-MS is to the absolute and relative matrix effect (ME) when coupled with CPE for measurements in human plasma. Three combinations of the surfactant Triton X-114 concentration (1.5% or 6%) and extraction temperature (40 or 55 °C) in six pH values gave over 1300 analyte-sample preparation condition pairs. A new term – surfactant effect (calculated for the standard solution) – allowed us to distinguish between the surfactant effect and that related to interferences from human plasma. The screening revealed that CPE combined with LC–MS is not related to a significant ME in the optimal pH of extraction. A significant absolute ME (<85% or>115%) was observed only for 25% of the analytes. Data processing (principal component analysis, classification trees, partial least squares-discriminant analysis) based on the extraction conditions and molecular descriptors helped to identify compounds prone to the matrix effect and speed up method development. A low surfactant concentration and low temperature decreased both the absolute and relative ME. pH of the extraction influenced only the relative ME. Low retention time reduced the risk of relative ME, whereas high polarity and the possibility of hydrogen bond formation minimized the occurrence of the surfactant effect and absolute ME. A significant relative ME (>15%) was observed only for 11% of the compounds, thus CPE merged with LC–MS allowed to measure drug concentrations in a reliable manner for majority of compounds. The presented approach may be further applied to other analytes and matrices. [ABSTRACT FROM AUTHOR]

Highlights • Screening and confirmatory analysis is proposed for polar endogenous compounds. • No need for instrumental modification to switch from screening to confirmatory steps. • C18 column is used in both analyses by modifying mobile phase composition. • Applicability of the method is checked with creatinine, polyamines and amino acids. Abstract In this paper, a high-throughput approach is proposed for the sensitive screening and the confirmatory analysis of polar compounds in saliva using a two-step approach based on a liquid chromatographic system coupled to a triple quadrupole mass spectrometer. A reversed-phase chromatographic column was used in both steps and changes in the composition of the mobile phase allowed the screening and the confirmatory analyses to be performed with the same instrumental configuration. The proposed strategy has been tested for the determination of a multiclass group of polar endogenous compounds (creatinine, polyamines and amino acids) in saliva samples. The validation of the entire procedure showed consistent results for all the compounds in both steps. Repeatability and reproducibility were evaluated for both procedures, with values below 8% in the case of repeatability and 17% in the case of reproducibility. The instrumental limits of detection were found to be between 1.22 × 10−3 and 46.1 × 10−3 mg/L for creatinine and lysine, respectively, and accuracy of the method was evaluated in terms of apparent recoveries and values were found to be between 80 and 127%. Matrix effects were evaluated and it was found that the analytical outcome was influenced by the matrix of the sample. Thus, a one-point standard addition method was used for quantification. The optimized two-step procedure was applied to saliva samples from apparent healthy volunteers. Overall, satisfactory results were obtained in both steps, demonstrating its applicability for quantitative analysis of polar endogenous compounds in this kind of matrices. [ABSTRACT FROM AUTHOR]

Highlights • Retention models allow for optimizing advanced chromatographic techniques. • van 't Hoff plot curvature is common at 98% of datasets tested. • Three models were compared for their ability to predict retention and enthalpy. • Pappa-Louisi's adsorption model is best for both retention and enthalpy modelling. Abstract Predicting retention and enthalpy allows for the simulation and optimization of advanced chromatographic techniques including gradient separations, temperature-assisted solute focusing, multidimensional liquid chromatography, and solvent focusing. In this paper we explore the fits of three expressions for retention as a function of mobile phase composition and temperature to retention data of 101 small molecules in reversed phase liquid chromatography. The three retention equations investigated are those by Neue and Kuss (NK) and two different equations by Pappa-Louisi et al., one based on a partition model (PL-P) and one based on an adsorption model (PL-A). More than 25 000 retention factors were determined for 101 small molecules under various mobile phase and temperature conditions. The pure experimental uncertainty is very small, approximately 0.22% uncertainty in retention factors measured on the same day (2.1% when performed on different days). Each of the three equations for ln(k) was fit to the experimental data based on a least-squares approach and the results were analyzed using lack-of-fit residuals. The PL-A model, while complex, gives the best overall fits. In addition to examining the equations' adequacy for retention, we also examined their use for apparent retention enthalpy. This enthalpy can be predicted by taking the derivative of these expressions with respect to the inverse of absolute temperature. The numerical values of the fitted parameters based on retention data can then be used to predict retention enthalpy. These enthalpy predictions were compared to those obtained from a modified van 't Hoff equation that included a quadratic term in inverse temperature. Based on analysis of 1 211 van 't Hoff plots (solute-mobile phase-day combinations), ninety-eight percent showed a significantly better fit when using the modified van 't Hoff expression, justifying its use to provide apparent enthalpies as a function of mobile phase composition and temperature. The foregoing apparent enthalpies were compared to the apparent enthalpies predicted by the three models. The PL-A model, which contains a temperature dependent enthalpy, provided the best enthalpy prediction. However, there is virtually no correlation between the overall lack of fit to experimental ln(k) for each model and the corresponding lack of fit of the linear (in 1/T) van 't Hoff expression. Thus, the temperature-dependent enthalpy is apparently not the cause of a model's ability to fit ln(k) as a function of mobile phase composition and temperature. The value in these expressions is their ability to predict chromatograms, allowing for optimization of an advanced chromatographic technique. The two simpler models NK and PL-P, which do not contain a temperature dependent enthalpy, have their merits in modelling retention (NK being the better of the two) and enthalpy (PL-P being the better of the two) if a simpler expression is required for a given application. [ABSTRACT FROM AUTHOR]

Abstract: This paper demonstrates an experimental application of the nonlinear frequency response (FR) method extension to determine adsorption isotherms of binary mixtures. This method, based on the analysis of the response of a chromatographic column subjected to the sinusoidal inlet concentration changes, is shown to be an alternative for isotherm determination. The critical issue related to the successful application of the method is to reach experimentally the low frequency asymptotic behaviour of the corresponding frequency response functions (FRFs). Although, there are different possibilities to perform periodical inlet concentration changes, in this paper only simultaneous changes for both components were considered. The adsorption of phenol and 2-phenylethanol on octadecyl silica was analyzed experimentally using a mixture of methanol and water as a solvent. Parameters of competitive isotherms were also estimated for comparison using the classical perturbation method. Despite certain differences between competitive isotherms estimated with the two methods that were found, the obtained results show the potential of the nonlinear FR method for measuring competitive isotherms. [Copyright &y& Elsevier]

Abstract: A systematic study was made on the identification and quantitative determination of polynuclear aromatic hydrocarbons (PAHs) in heavy products derived from coal and petroleum with high performance liquid chromatography (HPLC). After the separation of PAHs by a high-resolution column, identification was made through four methods: (1) the relative retention time (RRT) method, (2) the stop-flow-UV scanning method, (3) the method of fluorescence characteristic index Φ′ and (4) the method of V′ index at different UV wavelengths. For the quantitative determination of the components, methods of external standard (E-X), internal standard (I-N) and external standard-response factors (E-F) were compared. The E-F method was recommended by the present paper. For the determination of quantitative response factors (F) two methods were studied, including the HPLC peak-area method (Peak-area method) and the UV absorbance method using a UV spectrometer (absorbance method). The absorbance method was better and is recommended by the present paper. The F values of 30 PAHs from the two different methods are given. The samples analyzed include a coal tar pitch, a thermal cracking residue oil and a residual oil from ethylene production. [Copyright &y& Elsevier]

Abstract: In this paper, we describe a strategy that can be used to efficiently develop a high-performance liquid chromatography (HPLC) separation of challenging pharmaceutical molecules. This strategy involves use of advanced chromatographic technologies, such as a computer-assisted chromatographic method development tool (ChromSword) and an automated column switching system (LC Spiderling). This process significantly enhances the probability of achieving adequate separations and can be a large time saver for bench analytical scientists. In our study, the ChromSword was used for mobile phase screening and separation optimization, and the LC Spiderling was used to identify the most appropriate HPLC columns. For proof of concept, the analytes employed in this study are the structural epimers betamethylepoxide and alphamethylepoxide (also known as 16-beta methyl epoxide and 16-alpha methyl epoxide). Both of these compounds are used in the synthesis of various active pharmaceutical ingredients that are part of the steroid pharmaceutical products. While these molecules are relatively large in size and contain various polar functional groups and non-polar cyclic carbon chains, their structures differ only in the orientation of one methyl group. To our knowledge, there is no reported HPLC separation of these two molecules. A simple gradient method was quickly developed on a 5cm YMC Hydrosphere C18 column that separated betamethylepoxide and alphamethylepoxide in 10min with a resolution factor of 3.0. This high resolution provided a true baseline separation even when the concentration ratio between these two epimers was 10,000:1. Although outside of the scope of this paper, stability-indicating assay and impurity profile methods for betamethylepoxide and for alphamethylepoxide have also been developed by our group based on a similar method development strategy. [Copyright &y& Elsevier]

Abstract: Molecularly imprinted polymers (MIPs) are synthetic polymers having a predetermined selectivity for a given analyte, or group of structurally related compounds, that make them ideal materials to be used in separation processes. In this sense, during past years a huge amount of papers have been published dealing with the use of MIPs as sorbents in solid-phase extraction, namely molecularly imprinted solid-phase extraction (MISPE). Although the majority of these papers were restricted to describe the use of different templates for different applications, several attempts proposing new alternatives to minimize the inherent drawbacks of the preparation and use of MIPs (i.e. template bleeding, tedious synthesis procedure, etc.) have been reported. Thus, this paper does not pretend to be a collection of MISPE-related papers but to give an overview on the significant attempts carried out during recent years to improve the performance of MIPs in solid-phase extraction. In addition, the use of MIPs packed in high performance liquid chromatography (HPLC) columns for the direct injection of crude sample extracts and the preparation of imprinted fibres for solid-phase microextraction will be also discussed. [Copyright &y& Elsevier]

Abstract: A simple and sensitive method for the determination of abietic acid and dehydroabietic acid in food samples was developed using a fully automated method consisting of in-tube solid-phase microextraction (SPME) coupled with liquid chromatography–mass spectrometry (LC/MS). These compounds were separated within 5min by HPLC using an ODS-3 column and 5mM ammonium formate/acetonitrile (10/90, v/v). Electrospray ionization conditions in the negative ion mode were optimized for MS detection of abietic acid and dehydroabietic acid. The optimum in-tube SPME conditions were 20draw/eject cycles of 40μL of sample using a Supel Q PLOT capillary column as an extraction device. The extracted compounds were easily desorbed from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME LC/MS method, good linearity of the calibration curve (r >0.9998) was obtained in the concentration range from 0 to 50ng/mL, and the detection limits (S/N=3) of abietic acid and dehydroabietic acid were 2.9 and 2.1pg/mL, respectively. The in-tube SPME method showed above 75-fold greater sensitivity than the direct injection method (5μL injection). This method was applied successfully to analysis of food samples without interference peaks. The recoveries of abietic acid and dehydroabietic acid spiked into liquid samples were above 79%, and the relative standard deviations were below 6.6%. These compounds were detected at ng/mL or ng/g levels in various liquid or solid food samples contacted with paper. [Copyright &y& Elsevier]

Abstract: This paper examines geometric scaling models for field flow fractionation systems to understand how channel dimensions affect resolution and retention. Specifically, the changing contribution of the instrumental plate height during miniaturization of field flow fractionation (FFF) systems is reported. The work is directed towards determining the optimal geometrical parameters for miniaturization of field flow fractionation systems. The experimental relationship between channel height in FFF systems and instrumental plate heights is reported. FFF scaling models are modified to: (i) better clarify the dependence of plate height and resolution on channel height in FFF and (ii) include a more complete geometrical scaling analysis and model comparison in the low retention regime. Electrical field flow fractionation has been shown to benefit from miniaturization, so this paper focuses on that subtype, but surprisingly, the results also indicate the possibility of improvement in performance with miniaturization of other field flow fractionation systems including general FFF subtypes in which the applied field does not vary with channel height. This paper also discusses the potential role of more powerful microscale field flow fractionation systems as a new class of sample preparation units for micro-total-analysis systems (μ-TAS). [Copyright &y& Elsevier]

Abstract: The potential of solid-phase extraction coupled on-line to liquid chromatography/electrospray tandem mass spectrometry (SPE-LC–ESI-MS/MS) has been investigated in this paper for the efficient sensitive quantification and confirmation of 16 antibiotics in water. The list of targeted analytes included 10 quinolones (oxolinic acid (OXO), nalidixic acid (NAL), flumequine (FLU), marbofloxacine (MAR), ofloxacine (OFLO), enrofloxacine (ENR), pefloxacine (PEF), ciprofloxacine (CIP), pipemidic acid (PIPE), norfloxacine (NOR)) and 6 penicillins (penicillin G (PEN), oxacillin (OXA), dicloxacillin (DIC), piperacillin (PIP), cloxacillin (CLO) and ampicillin (AMP)) that were determined in ground and surface water. The procedure is based on the injection of 9.8mL of sample into the SPE-LC–MS/MS system and the measurement of antibiotics by selected reaction monitoring mode, using a triple quadrupole analyser. The method has been validated at realistic low concentrations that might be present in environmental water, i.e. 10 and 100ngL−1, obtaining recoveries between 74% and 123% with relative standard deviation lower than 14%. Matrix effects were not relevant in most of cases, except for ampicillin in surface water, where notable signal suppression was observed. The limits of detection were as low as 0.4–4.3ngL−1. The method developed allows the rapid screening and quantification of all the analytes selected by acquiring one MS/MS transition (normally the most sensitive) for each compound. It was applied to a number of actual surface and groundwater samples with several compounds being detected, mainly quinolones, at low ngL−1 levels. Special attention was given to the confirmation of compounds detected in water due to the difficulties of obtaining confident confirmation at low ngL−1. This matter has been of growing concern in the last few years as reflected by recent papers and correspondence. The acquisition of several MS/MS transitions for each compound detected in a second independent analysis allowed the unequivocal confirmation of identity, avoiding reporting false-positives. Finally, the potential of QTOF instruments to confirm positive samples has also been evaluated and compared with triple quadrupole analysers. [Copyright &y& Elsevier]

Abstract: The chemometric resolution and quantification of overlapped peaks from comprehensive two-dimensional (2D) liquid chromatography (LC×LC) data are demonstrated. The LC×LC data is produced from an in-house LC×LC analyzer that couples an anion-exchange column via a multi-port valve with a reversed-phase column connected to a UV absorbance detector. Three test mixtures, each containing a target analyte, are subjected to partial LC×LC separations to simulate likely cases of signal overlap. The resulting unresolved target-analyte signals are then analyzed by the standard-addition method and two chemometric methods. The LC×LC analyses of a test mixture and its corresponding standard-addition mixture results in two data matrices, one for each mixture. The stacking of these two data matrices produces a data structure that can then be analyzed by trilinear chemometric methods. One method, the generalized rank annihilation method (GRAM), uses a non-iterative eigenvalue-based approach to mathematically resolve overlapped trilinear signals. The other method, parallel factor analysis (PARAFAC), uses an iterative approach to resolve trilinear signals by the optimization of initial estimates using alternating least squares and signal constraints. In this paper, GRAM followed by PARAFAC analysis is shown to produce better qualitative and quantitative results than using each method separately. For instance, for all three test mixtures, the GRAM-PARAFAC approach improved quantitative accuracy by at least a factor of 4 and quantitative precision by more than 2 when compared to GRAM alone. This paper also introduces a new means of correcting run-to-run retention time shifts in comprehensive 2D chromatographic data. [Copyright &y& Elsevier]

Abstract: An extension of the treatment adopted in a recent paper [P. Nikitas, A. Pappa-Louisi, P. Agrafiotou, J. Chromatogr. A 946 (2002) 33] was used to derive expressions describing the variation of solute retention k with composition in ternary reversed phase liquid chromatography, RP-LC, solvent systems. The equation of the partition model obtained in this way for a ternary mobile phase was identical to that previously derived using the solubility parameter concept. This equation as well as two new expressions of ln k versus organic modifiers content were tested in a variety of ternary solvent systems in order to examine the possibility of predicting retention behavior of solutes under ternary solvent mixture elution conditions from known retention characteristics in binary mobile phases. It was demonstrated the superiority of both new equations derived in this paper to that previously proposed and applied to date in ternary solvent mixtures. [Copyright &y& Elsevier]

Abstract: Fosinopril sodium presents a prodrug for the active angiotensin converting enzyme (ACE) inhibitor, fosinoprilat. The dual elimination of fosinoprilat by the liver and the kidney distinguishes fosinopril from other angiotensin converting enzyme inhibitors. Such ways of elimination are important for antihypertensive therapy of patients on haemodialysis. The paper presents development and evaluation of a new and sensitive liquid chromatographic (LC) method for the analysis of fosinoprilat in plasma obtained from patients on haemodialysis. A microemulsion system mixture as mobile phase has been used for the separation and analysis of fosinoprilat in plasma samples. The plasma samples were injected directly onto the HPLC system (Waters Breeze) after appropriate sample dilution with mobile phase. Separations were performed on the Bakerbond ENV 4.6mm×150mm, 5μm particle size column with UV detection at 220nm. The flow rate was 1.00mLmin−1. The mobile phase consisted of 1.0% (w/v) of diisopropyl ether, 2.0% (w/v) of sodium dodecyl sulphate (SDS), 6.0% (w/v) of n-propanol and 91% (w/v) of aqueous 25mM di-sodium hydrogen phosphate, pH adjusted to 2.8 with 85% orthophosphoric acid. The developed method was then subjected to method validation according to the criteria stated in the FDA bioanalytical method validation guidance. The results for specificity, linearity, low limit of quantification (LLOQ), precision, accuracy and stability were within the accepted criteria. The unique approach applied in this paper makes possible the determination of fosinoprilat even in the presence of metabolites of other drugs, so the method can be used for obtaining the reliable results in a fast and simple way. [Copyright &y& Elsevier]

Both LC and capillary LC (CapLC) have been successfully interfaced with inductively coupled plasma mass spectrometry (ICP-MS). Gradients of acetonitrile and aqueous based solvents have been employed to separate several compounds of pharmaceutical interest. This paper will describe four application areas in the pharmaceutical industry, and examples will be shown where CapLC, LC and gel electrophoresis via laser ablation have been coupled with ICP-MS. The four areas highlighted in this paper are: (1) the use of derivatisation reactions to “make the invisible visible”. Methods involving derivatisations with copper and iron will be described that can be used for the analysis of amines and carboxylic acids by ICP-MS. (2) The profiling of metal ion content (in particular bromine) in biological samples such as human plasma, this study will focus on the metabolism of bromine-labelled peptides (e.g. substance P). (3) The analysis of materials derived from single, solid-phase beads used in combinatorial chemistry, and (4) also discussed will be our findings from investigations into the use of laser ablation ICP-MS on the determination of protein phosphorylation on electrophoresis gel blots. [Copyright &y& Elsevier]

A characteristic feature of synthetic polymers is their dispersity in molar mass and, in many cases, chemical composition. Since dispersity is highly relevant in relation to polymer properties, ongoing efforts are being put in the development of appropriate analysis methods. In this respect, size-exclusion chromatography (SEC) is well known for the determination of molar mass distributions. Methods for chemical composition distributions are less mature than SEC and mainly include liquid chromatography and mass spectrometry and the combination of these techniques. The term chemical composition distribution is considered broad in this paper, i.e. for the chemical composition distribution of a (co)polymer backbone, for the functionality type distribution of a polymers’ functional end groups, for the block length distribution of a block copolymer, for the branching distribution and for the tacticity distribution. In this paper, analysis methods for all types of chemical composition distributions are reviewed. Special attention is paid to practical requirements and common misconceptions that sometimes arise. Applications within the last 5 years are summarized. [Copyright &y& Elsevier]

The results of research on the optimization of the thin-layer chromatography–flame ionisation detection for the determination of group composition of natural base oils, including separation of the aromatics into subgroups, are presented. Neutral base oils obtained in several steps of refining from vacuum distillation petroleum fractions are the most difficult to analyze by hydrocarbon group type analysis (HGTA) because of the high content of aliphatic fragments in their molecules. Factors affecting the accuracy and precision of the results were identified. The paper presents the analytical procedure, including two different calibration methods, as well as the results of studies on the reproducibility of HGTA of typical base oils of different viscosity classes under the optimized conditions. The same conditions were found suitable for HGTA of other high-boiling petroleum fractions by TLC with flame ionisation detection. The paper also introduces a new procedure for reproducible determination of polar fractions in base oils utilizing solid-phase extraction columns, and presents a corrected procedure for the determination of saturated compounds and aromatics (mono-, bi- and polycyclic) in base oils by column liquid chromatography. [Copyright &y& Elsevier]

• Hierarchically porous UiO-66@SiO 2 microspheres were synthesized by H 2 O 2 etching. • A baseline separation of small solutes can be achieved on HP-UiO-66@SiO 2 column. • The narrower peak widths and higher resolution were achieved. • The plate number of HP-UiO-66@SiO 2 column can reach to be 134,459/m for fluorene. Metal organic frameworks (MOFs) show promise to be employed as stationary phase for high performance liquid chromatography (HPLC), however, the microporous structures of MOFs seriously restrict the diffusion and mass transfer of solute molecules, leading to a low column efficiency. In this paper, the fabrication of hierarchically porous UiO-66@SiO 2 (HP- UiO-66@SiO 2) core-shell microspheres via H 2 O 2 etching has been proposed as a viable approach to enhance the separation performance of MOFs-based columns for HPLC. Through the direct treatment of the preliminary prepared UiO-66@SiO 2 microspheres with H 2 O 2 etching, HP-UiO-66@SiO 2 core-shell microspheres were successfully synthesized with an enlarged pore size of up to 9 nm, facilitating efficient mass transfer in chromatographic separation. The prepared HP-UiO-66@SiO 2 core-shell microspheres were then explored as stationary phase in HPLC to separate the nonpolar alkyl benzene homologues, the polar aromatic alcohol homologues and the xylene isomers. The results indicated that the baseline separations of these solutes were achieved successfully with narrow peak width and higher resolution than the UiO-66@SiO 2 column. The HP-UiO-66@SiO 2 column exhibited superior separation performance, reaching a maximum plate number of 134,459/m for fluorene, and showing good reproducibility. As a result, this template-free approach suggests that the fabrication of hierarchically porous MOFs@silica core-shell microspheres is a successful approach to enhance the column efficiency of MOFs-based columns in HPLC. [ABSTRACT FROM AUTHOR]

• Error model considers pump delays, pump flow rate, and loading concentration. • Kernel density estimation of error model. • Bayesian uncertainty quantification based on Markov chain Monte Carlo simulations. • Code and case studies published as open source code. Current mechanistic chromatography process modeling methods lack the ability to account for the impact of experimental errors beyond detector noise (e.g. pump delays and variable feed composition) on the uncertainty in calibrated model parameters and the resulting model-predicted chromatograms. This paper presents an uncertainty quantification method that addresses this limitation by determining the probability distribution of parameters in calibrated models, taking into consideration multiple realistic sources of experimental error. The method, which is based on Bayes' theorem and utilizes Markov chain Monte Carlo with an ensemble sampler, is demonstrated to be robust and extensible using synthetic and industrial data. The corresponding software is freely available as open-source code at https://github.com/modsim/CADET-Match. [ABSTRACT FROM AUTHOR]

• Revealed the potential chemical behavior of electron-rich aniline compounds and Si-OH in the stationary phase of the chromatographic column during the RP-HPLC separation process. • It is found that increasing the Ionic strength in the mobile phase is helpful to alleviate or shield the influence of the contact between Si-OH and aniline compounds in the column. • Developed a simple and effective method to solve the problem of ghost peaks generated by the contact reaction between aniline compounds and Si-OH in the chromatographic column during the analysis of substances related to electron-rich aniline compounds. • This study suggested that for electron-rich aniline compounds, the addition of buffer salts or inorganic salts to the mobile phase can not only improve the peak shape and resolution but also improve the stability of the compounds in the column. Two "ghost peaks" appeared in the process of developing an impurities analytical method for an electron-rich aniline compound by RP-HPLC. Surprisingly, the "ghost peaks" disappeared when the mobile phase was re-prepared. The "ghost peak" slowly began to reappear and gradually increased after increasing the injection volume or changing different instruments and columns. In this paper, the structures of two "ghost peaks" were analyzed by LC-MS/MS, which were identified as the dimer of the main peak and the oxidation products of the dimer. The mechanism was confirmed by studying the "ghost peaks" appearance phenomenon in the mobile phase with different pH values, different types of buffer salts, and different brand chromatographic columns. The potential chemical behavior of this type of compound on the column was clearly revealed in the process of RP-HPLC separation. The coupling reaction of electron-rich aniline compounds can be induced by partial or complete dissociation of the silanol group to Si- O −in the stationary phase of a reversed-phase chromatographic column under neutral and basic conditions of the mobile phase. Adding inorganic salts to the mobile phase can inhibit the reaction, and the higher salt concentration, the stronger the effect. [ABSTRACT FROM AUTHOR]

In this paper, a monolithic octadecylsilane column and particle-packed octadecylsilane columns were used to investigate the retention behaviors of oligonucleotides by ion-pair reversed-phase liquid chromatography (IP-RPLC). Results showed that, with same base composition, hairpin oligonucleotides always had weaker retention than corresponding random coil oligonucleotides on the monolithic column, but not on the particle-packed columns. In addition, the linear correlation between the retention factor k of oligonucleotides and the reciprocal of temperature (1/T), especially for hairpins, was relatively weaker on the particle-packed columns, as compared to the correlation on the monolithic column. The correlation between k and 1/T became weaker with decreasing particle size of the particle-packed columns. Moreover, results revealed that the overall retention order on the particle-packed column with small particles (3 μm) differed greatly from that on the monolithic column. In contrast, the retention order on the 10 μm particle-packed column was very close to that on the monolithic column. From the above, we inferred that oligonucleotides could keep their primary conformations unchanged when passing through the monolithic column, attributed to the special pore structures of the monolith. However, the conformations of oligonucleotides were suppressed or even destroyed when oligonucleotides passed through the particle-packed columns. This because the narrow and tortuous channels created by the stacked stationary phase particles could lead to more complex and unequable retention behaviors. Therefore, the monolithic column exhibited better retention regularity for oligonucleotides of secondary structure especially for hairpins than the particle-packed columns. It is noteworthy that the monolith-based IP-RPLC opens an intriguing prospect in accurately elucidating the retention behaviors of oligonucleotides. [ABSTRACT FROM AUTHOR]

Anabolic and androgenic steroids (AAS) are banned substances in both human and equine sports. They are often administered intramuscularly to horses in esterified forms for the purpose of extending their time of action. The authors’ laboratory has previously reported an UHPLC/HRMS method using quadrupole-Orbitrap mass spectrometer in full scan and parallel reaction monitoring (PRM) mode for the detection of 48 AAS and/or their esters in horse hair. However, two injections were required due to the long duty cycle time. In this paper, an UHPLC/HRMS method using multiplexed targeted MS 2 mode was developed and validated to improve the coverage to 65 AAS and/or their esters in a single injection. In addition, a GC/MS/MS method in selected reaction monitoring (SRM) mode was developed to screen for another seven AAS and/or their esters not adequately covered by the UHPLC/HRMS method using the same sample extract after derivatisation with pentafluoropropionic anhydride. The UHPLC/HRMS and GC/MS/MS methods in combination allowed the detection of 72 AAS and/or their esters with estimated limits of detection down to sub to low ppb levels with good interday precision. Method applicability was demonstrated by the detection of boldione and 4-androstenedione in two out-of-competition hair samples and testosterone propionate in a referee hair sample. [ABSTRACT FROM AUTHOR]

Liquid chromatographic ligand-exchange chiral stationary phases (CSPs) have been developed for the resolution of racemic compounds, which can be used as bidentate or tridentate ligands. In this paper, we review the development of liquid chromatographic ligand-exchange CSPs based on amino alcohols or their derivatives coated dynamically on octadecylsilica gel or bonded covalently to silica gel and their applications to the resolution of α-amino acids, β-amino acids, α-hydroxycarboxylic acids and proton pump inhibitors (PPIs). The relationship between the structures of CSPs and chromatographic resolution behaviors is discussed. In particular, a rational approach to the development of improved ligand-exchange CSPs based on amino alcohols derived from α-amino acids is followed. [ABSTRACT FROM AUTHOR]

Methylstenbolone (2,17α-dimethyl-5α-androst-1-en-17β-ol-3-one) is a synthetic anabolic and androgenic steroid (AAS) sold as an oral ‘nutritional supplement’ under the brand names ‘Ultradrol’, ‘M-Sten’ and ‘Methyl-Sten’. Like other AASs, methylstenbolone is a prohibited substance in both human and equine sports. This paper describes the studies of the in vitro and in vivo metabolism of methylstenbolone in horses using LC/HRMS, GC/MS and GC/MS/MS. Phase I in vitro metabolic study of methylstenbolone was performed using homogenised horse liver. Hydroxylation was the only biotransformation observed. Six in vitro metabolites were detected including four mono-hydroxylated metabolites, namely 16α/β-hydroxymethylstenbolone (M1a, M1b), 20-hydroxymethylstenbolone (M1c), 6-hydroxymethylstenbolone (M1d), and two dihydroxylated methylstenbolone metabolites (M2c–M2d). An in vivo experiment was carried out using two retired thoroughbred geldings. Each horse was administered with 100 mg methylstenbolone supplement by stomach tubing daily for three consecutive days. Methylstenbolone and 14 metabolites were detected in the post-administration urine samples. The proposed in vivo metabolites included 16α/β-hydroxymethylstenbolone (M1a, M1b), 20-hydroxymethylstenbolone (M1c), two dihydroxylated methylstenbolone (M2a, M2b), 17- epi -methylstenbolone (M3), methasterone (M4), 2,17-dimethylandrostane-16,17-diol-3-one (M5), dihydroxylated and reduced methylstenbolone (M6), 2α,17α-dimethylandrostane-3α,17β-diol (M7), 2,17-dimethylandrostane-3,16,17-triol (M8a–M8c) and 2,17-dimethylandrostane-2,3,16,17-tetraol (M9), formed from hydroxylation, reduction and epimerisation. Methylstenbolone and ten of its metabolites could be detected in post-administration plasma samples. The highest concentration of methylstenbolone detected in urine was about 10–36 ng/mL at 3–4 h after the last administration, while the maximum concentration in plasma was about 0.4–0.7 ng/mL at 1 h after the last administration. For controlling the misuse of methylstenbolone, M8c and M9 gave the longest detection time in urine, while M4, M5 and M6 were the longest detecting analytes in plasma. They could be detected for up to 5 and 4.5 days respectively in urine and plasma. Apart from 16α/β-hydroxymethylstenbolone (M1a, M1b), the methylstenbolone metabolites reported herein have never been reported before. [ABSTRACT FROM AUTHOR]

The transplacental passage of thyroid hormones (THs) is of great significance since the maternal THs are vitally important in ensuring the normal fetal development. In this paper, we determined the concentrations of seven THs, viz. L-thyroxine (T 4 ), 3,3′,5-triiodo- l -thyronine (T 3 ), 3,3′,5′-triiodo- l -thyronine (rT 3 ), 3,3′-diiodo- l -thyronine (T 2 ), 3,5-diiodo- l -thyronine (rT 2 ), 3-iodo- l -thyronine (T 1 ) and 3-iodothyronamine (T 1 AM), in placenta using isotope dilution liquid chromatography quadrupole time-of-flight mass spectrometry. We optimized the method using isotopically labeled quantification standards ( 13 C 6 -T 4 , 13 C 6 -T 3 , 13 C 6 -rT 3 and 13 C 6 -T 2 ) and recovery standard ( 13 C 12 -T 4 ) in combination with solid-liquid extraction, liquid–liquid extraction and solid phase extraction. The linearity was obtained in the range of 0.5–150 pg uL −1 with R 2 values >0.99. The method detection limits (MDLs) ranged from 0.01 ng g −1 to 0.2 ng g −1 , while the method quantification limits (MQLs) were between 0.04 ng g −1 and 0.7 ng g −1 . The spike-recoveries for THs (except for T 1 and T 1 AM) were in the range of 81.0%–112%, with a coefficient of variation (CV) of 0.5–6.2%. The intra-day CVs and inter-day CVs were 0.5%–10.3% and 1.19%–8.88%, respectively. Concentrations of the THs were 22.9–35.0 ng g −1  T 4 , 0.32–0.46 ng g −1  T 3 , 2.86–3.69 ng g −1 rT 3 , 0.16–0.26 ng g −1  T 2 , and < MDL for other THs in five human placentas, and 2.05–3.51 ng g −1  T 4 , 0.37–0.62 ng g −1  T 3 , 0.96–1.3 ng g −1 rT 3 , 0.07–0.13 ng g −1  T 2 and < MDL for other THs in five mouse placentas. The presence of T 2 was tracked in placenta for the first time. This method with improved selectivity and sensitivity allows comprehensive evaluation of TH homeostasis in research of metabolism and effects of environmental contaminant exposures. [ABSTRACT FROM AUTHOR]