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• Automated framework for parameter estimation of multi-component ion exchange chromatography models. • Model-based optimization of a purification included in the framework. • Experimental validation of the model using the obtained optimum. • Several options for optimal purification provided to the user. The current landscape of biopharmaceutical production necessitates an ever-growing set of tools to meet the demands for shorter development times and lower production costs. One path towards meeting these demands is the implementation of digital tools in the development stages. Mathematical modelling of process chromatography, one of the key unit operations in the biopharmaceutical downstream process, is one such tool. However, obtaining parameter values for such models is a time-consuming task that grows in complexity with the number of compounds in the mixture being purified. In this study, we tackle this issue by developing an automated model calibration procedure for purification of a multi-component mixture by linear gradient ion exchange chromatography. The procedure was implemented using the Orbit software (Lund University, Department of Chemical Engineering), which both generates a mathematical model structure and performs the experiments necessary to obtain data for model calibration. The procedure was extended to suggest operating points for the purification of one of the components in the mixture by means of multi-objective optimization using three different objectives. The procedure was tested on a three-component protein mixture and was able to generate a calibrated model capable of reproducing the experimental chromatograms to a satisfactory degree, using a total of six assays. An additional seventh experiment was performed to validate the model response under one of the suggested optimum conditions, respecting a 95 % purity requirement. All of the above was automated and set in motion by the push of a button. With these results, we have taken a step towards fully automating model calibration and thus accelerating digitalization in the development stages of new biopharmaceuticals. [ABSTRACT FROM AUTHOR]

We present a new chromatogram decomposition method for Gas Chromatography (GC) which represents a chromatogram as a sum of template functions inspired by the analytic solution of mass balance equation. The proposed method starts by approximating GC response of a single gas by these template functions. Consequently, it utilizes the temporal translation and dilation of this approximate response to approximate GC responses of other gases of interest. The results are demonstrated on lab data using calibration bottles containing mixtures of C 1 - C 5. Correlation of the amplitudes of the decomposed responses and injected concentrations indicates linear calibration curves are sufficient to estimate C 1 - C 5 concentrations. The performance of the method is demonstrated by a ratio test where a calibration bottle with C 1 concentration 300 times larger than C 2 and C 3 concentrations is injected into GC. • Expressing response of a GC system to a single gas using functions inspired by the analytic solution of a mass balance equation. • Approximating responses of a GC system to other gases as an affine transformed version of response of the single gas. • Calibration and subsequent quantitative analysis with an application for sensitivity analysis. [ABSTRACT FROM AUTHOR]

• Sample brought directly in thermal desorption tube without adsorbent. • Proper calibration is not evident since it can't be done in similar way as sample. • Calibration issues were investigated using offline and inline liquid calibration. • Problem could be attributed to diluent (illustrated with water and toluene). • Insertion of LiCl plug in thermal desorber tube to remove water offered solution. A thermal desorber (TD) can be used in different ways to introduce samples in a gas chromatographic (GC) system. Besides its conventional use where the collected analytes are released from the sorbent in the sample tube, direct dynamic desorption (DDD) is an interesting option where a solid sample is put directly in the TD tube. However, since no sorbent is used for the sample, proper calibration is not straightforward. This issue was investigated in the present work using offline liquid calibration (OLC) and inline liquid calibration (ILC). Unexpectedly, ILC yielded a lower response than OLC. This could be related to the adsorption kinetics of the analytes and water on the cold trap of the TD. More insight was gained performing double injection ILC experiments with toluene as diluent for the analytes and injecting water before or after the toluene solution. This revealed a clear influence of the diluent. The influence of water was further explored applying two cold trap temperatures (4 °C and −30 °C). Inserting a LiCl trap in the TD tube to capture the water was found to be an effective solution for the problem. Finally, quantitative aspects of this approach were demonstrated. [ABSTRACT FROM AUTHOR]

• Importance of sufficient ionic strength (buffer capacity) of LC–MS mobile phases. • Improving chromatographic peak shape of ionic analytes. • Analyte response as a function of modifier concentration in LC–MS mobile phase. • Chromatographic peak splitting due to the presence of matrix compounds. • Aging of liquid chromatography stationary phases. A routine multiresidue method developed for the detection and quantification of veterinary drug residues in animal-based food was used to analyze sheep (ovine) liver. Unlike when working with previously validated matrices (e.g., bovine liver), some of the analytes of interest chromatographed in the form of split- or even fully baseline separated peaks. In other cases a significantly longer retention times (tR) was observed. A detailed investigation led to the elucidation of taurocholic acid as the causative agent. This compound is present in sheep liver at significantly higher concentrations than in most other animal tissues. Taurocholic acid is a zwitterionic compound and likely acts as an ion pairing agent, which modifies the selectivity of the stationary phase in a highly spatial and dynamic way. Injecting smaller volumes of matrix extract or the use of a significantly higher formic acid concentration in the mobile phase reduced or even completely eliminated the peak splitting. A more detailed examination led to the observation that the problem is not restricted to this particular matrix and extraction procedure or the used stationary phase. In fact, a higher formic acid concentration (e.g., 1.0 % versus 0.1 %) significantly improves the peak shape of many analytes present in fortified matrix samples as well as in pure standard solutions. In addition, analytical column aging was observed as being slower with a higher formic acid concentration. Finally the peak shape of analytes interacting with the metallic parts along the flow path of the liquid chromatograph was also significantly improved. Use of 0.1 % acid in mobile phases is often taken for granted in LC-MS. Regardless of the stationary phase, a higher ionic strength better stabilizes the pH and reduces unwanted interactions, which ultimately improves the method robustness. Flow injection experiments often show that 0.1 % acid concentrations produce the highest analyte signals. Yet, the use of 1 % acid in the mobile phase often leads to narrower and therefore taller chromatographic peaks, which may lead to lower detection limits for many analytes and to an improved separation efficiency. [ABSTRACT FROM AUTHOR]

• The risk of bisphenols (BPA, BPF, and BPS) in thermal papers and canned food samples was assessed. • A method for determining bisphenols based on HPLC-DAD was developed and validated. • An integrated calibration method was modified and supported by the H-point standard addition method to compensate interference effects. • BPA concentration in canned food products was exceeded. • Risk factors connected to the receipts (BPF and BPS) proved harmful to cashiers due to long exposure time. The most crucial purpose of the measurement is to obtain a reliable result that reflects the actual qualitative and/or quantitative features of the tested material. The overriding goal of analytical chemistry is to obtain accurate results after compensating of various interference effects as well as non-linear calibration dependence. A new approach based on an integrated calibration method (ICM) supported by H-point standard addition method (HPSAM) has been used to improve the quality of analytical results. The proposed methodological approach was extended using the step-by-step dilution procedure, and five measurement conditions were used to eliminate multiplicative, additive, and non-linear interferences. On this basis, a set of estimations is obtained to improve the quality of the analytical results. The analytical usefulness of the proposed approach was tested on the example of the determination of three compounds from the group of bisphenols (BPs) using the chromatographic technique - HPLC-DAD (high-performance liquid chromatography with diode array detection). Compared to the reference method - fluorescence spectroscopy - the obtained results were characterized by excellent accuracy (RE=3 % in most cases). The developed methodology allowed to carry out a risk assessment on BPA, BPF, and BPS present in samples of shop receipts and canned food. Store clerks have been shown to be particularly vulnerable to PBF and BPS in receipts due to skin permeation (exposure factors were equal to 308.97 µg/g for BPF and 181.89 µg/g for BPS). Consumers should also pay close attention to the BPA found in canned food samples (the average concentration was equal to 20.61 µg/mL, and the tolerable daily intake was exceeded over 165.000 times). The analytical method and the methodological approach were evaluated using the RGB model and the AGREE approach - it was shown that the method can be successfully used for other analytical purposes (the method is White) and is environmentally friendly (Significance=0.63). [ABSTRACT FROM AUTHOR]

• A novel SEC technique is proposed for the MWD characterization of ethyleneamines. • Narrow standard SEC calibration is applied using ethyleneamines. • The positively-charged packing material prevents adsorption of the ethyleneamines. • Good repeatibility of MW averages and MW distribution was achieved. Ethyleneamines have been produced and commercialized for decades in the chemical industry for a diverse range of applications. The presence of amine functional groups provides them opportunity to adsorb onto surfaces which can make them a very challenging sample matrix to analyze using separation techniques. In the present report, a new aqueous SEC-RI method, which enables MWD characterization of higher ethyleneamines, is described. The sample preparation was based on the dilute-and-shoot methodology. A surface-modified SEC column with positively charged groups attached to the stationary phase was used. The mobile phase composition (salt concentration, pH) was optimized to suppress interaction between the ethyleneamines and the packing material. Very symmetrical peak shapes were achieved for low MW monodisperse ethyleneamines despite their high primary amine content. MWD calculations were conducted using conventional narrow standard calibration with partial linear extrapolation of the calibration curve. The narrow standards were of the same chemistry as the samples of interest. Consequently, the standard components display a consistent behaviour towards the column packing as the sample components which makes the present method more robust and the interpretation of the quantitative results more convenient. Effect on the measured MW averages and MW distribution due to various experimental parameters (e.g., system variability, mobile phase preparation, sample concentration) were investigated showing good repeatability (RSD < 2%) for M n , M w , and M z. [ABSTRACT FROM AUTHOR]

• Quantitative data from parallel artificial liquid membrane extraction are reliable. • High accuracy and precision were obtained from multiple sources of plasma. • High accuracy and precision were obtained with different operators. • High accuracy and precision were obtained under non-exhaustive conditions. • Stable isotopically labelled internal standards are recommended. The use of miniaturized systems with the possibility for automation has become increasingly popular in the field of bioanalysis. As a new approach to liquid phase microextraction in the 96-well format, parallel artificial liquid membrane extraction (PALME) was introduced in 2013. In the present work, the reliability of the quantitative data obtained with PALME was thoroughly evaluated. Amitriptyline, nortriptyline, quetiapine, venlafaxine, o-desmethylvenlafaxine, and fluoxetine were selected as model analytes. The analytes were extracted under non-exhaustive conditions from human plasma samples and the extracts were analyzed directly by LC-MS/MS. Accuracy was within ±15% and precision was <15% when the QC samples were prepared in both pooled plasma and in plasma from multiple sources. Accuracy and precision was superior when stable isotopically labelled (SIL) internal standards were used, as compared to structural analogue internal standards in the plasma samples from multiple sources. SIL internal standards are therefore recommended as the first choice. Assessment of accuracy and precision was also carried out with four different operators performing the extraction procedure, providing accuracy within ±15% and precision <15%. The extraction recoveries were in the range from 48 to 85 %, and non-exhaustive extraction of the analytes did not affect the accuracy and precision of the method. With the method described, up to 96 samples can be extracted with a total extraction time of 60 min and with a total consumption of organic solvent less than 0.4 mL for the whole wellplate. PALME is therefore a new approach to high-throughput sample preparation, providing accurate quantification, along with simple workflow, low consumption of organic solvent, and extensive sample clean-up. [ABSTRACT FROM AUTHOR]

• HPLC-CAD developed for direct chain length characterization of polySia. • HPLC-CAD was shown to provide the actual chain length of polySia. • CAD as an alternative for time consuming DMB-derivatization. • Application of HPLC-CAD for polySia quantification in a broad concentration range. Polysialic acid (polySia) is widely investigated in various biopharmaceutical applications (e.g. treatment of inflammatory neurodegenerative diseases), whereby a certain polySia chain length with an average degree of polymerization 20 (polySia avDP20) shows most promising effects. In this study, a rapid analytical method using a HPLC and charged aerosol detector (CAD) for the direct chain length characterization of biopharmaceutically relevant polySia was developed. It was evaluated as a fast alternative to the commonly used 1,2-diamino-4,5-methylenedioxybenzene (DMB) HPLC application. In contrast to HPLC-FLD, the CAD-application provides the actual chain length of polySia within ∼3 h. The reliability of the HPLC-CAD was evaluated with a commercial reference sample of known chain length and biotechnologically produced LC polySia (long chain polySia with a DP ∼130). Moreover, HPLC-CAD was successfully applied in the direct detection of oligo- and polySia until DP ∼65 and can be used to monitor the thermal hydrolysis and subsequent chromatographic isolation of polySia avDP20 (average degree of polymerization 20) without DMB sample derivatization. In addition, CAD was successfully applied for polySia quantification using a modified elution gradient. It was tested as a fast alternative to commonly used thiobarbituric acid (TBA) assay. A differentiation between LC polySia and smaller, hydrolysed polySia chains was intended and possible. For LC polySia and polySia avDP20, a quadratic relation between polySia mass-concentration and CAD signal was observed. In case of LC polySia, a quadratic dependency with a determination coefficient of R2 = 0.99 in a broad concentration range between 0.025 and 15 mg mL−1 was determined. Quantification of polySia avDP20 was found to have quadratic dependency with a determination coefficient of R2 = 0.99 in a concentration range between 0.02 and 0.25 mg mL−1. The HPLC-CAD was tested for quantification with polySia references of known concentration and showed high accordance with a concentration deviation ≤6.7%. The CAD quantification method was also applied in the polySia avDP20 production process and was compared to the TBA assay. Results of a correlation plot showed a high determination coefficient of R2 = 0.98. Overall, HPLC-CAD analysis was successfully tested as a suitable characterization and quantification application in the biopharmaceutical production of polySia. [ABSTRACT FROM AUTHOR]

• TDA-UV allows absolute sizing of Bovine milk-derived EVs over their entire size range. • TDA is able to detect minor changes in EV size. • TDA provides quantitative and purity assessment of isolated EVs. • TDA coupled to LIF is also applicable for the analysis of fluorescently labeled EVs. This study reports the development of a Taylor Dispersion Analysis (TDA) method for the size characterization of Extracellular Vesicles (EVs), which are highly heterogeneous nanoscale cell-derived vesicles (30–1000 nm). Here, we showed that TDA, conducted in uncoated fused silica capillaries (50 µm i.d.) using a conventional Capillary Electrophoresis instrument, is able to provide absolute sizing (requiring no calibration) of bovine milk-derived EVs in a small sample volume (∼ 7 nL) and over their entire size range, even the smallest ones (< 70 nm) not accessible via other techniques that provide nanoparticle sizing in suspension. TDA size measurements were repeatable (RSD < 10%) and the average EV sizes were found in the range of 120–210 nm, in very good agreement with those measured with Nanoparticle Tracking Analysis, commonly used for EV characterization. TDA allowed quantitative estimation of EVs for concentrations ≥ 2 × 1011 EVs/mL. Furthermore, TDA was able to detect minor changes in EV size (i.e. by ∼25 nm upon interaction with specific anti-CD9 antibodies of ∼150 kDa), and to highlight the impact of extraction methods (i.e. milk pretreatment: freezing, acid precipitation or centrifugation; the type of size-exclusion chromatography column) and of fluorescent labeling (i.e. intravesicular or surface labeling) on the isolated EV population size. In parallel to EV sizing, TDA allowed to detect molecular contaminants (average sizes ∼1–13 nm) present within the sample, rendering this method a valuable tool to assess the quality and quantity of EV isolates. [ABSTRACT FROM AUTHOR]

Highlights • Multi-way chromatographic calibration protocols are reviewed. • The relation between chemometric models and data is discussed. • Application examples in various fields are detailed. Abstract This review discusses recent advances in both theory and experiment regarding multi-way chromatographic calibration. The focus is directed towards the chemometric processing of multi-way data arrays in which one or more instrumental modes describe the elution time behavior across liquid or gas chromatographic columns, and the remaining ones are of spectroscopic nature, e.g. UV–vis absorption, fluorescence emission (either as vectors or matrices) or mass spectrometry. Successful multi-way data decomposition into profiles for the contributing components allows one to perform quantitative analysis of complex samples. Quantitative applications usually make appropriate use of the second-order advantage which is inherent to multi-way data processing, and reduce the complexity of the data to a virtual univariate calibration which is typical of classical analytical chemistry. A number of recent experimental works will be discussed to illustrate the above concepts. [ABSTRACT FROM AUTHOR]

Highlights • A Bayesian approach can be used for model calibration and quality assessment. • The approach enables a prediction-based model uncertainty assessment. • Mechanistic models can perform reliable extrapolations despite substantial parameter uncertainty. • A sole parameter uncertainty assessment is insufficient for evaluating model quality. Abstract Mechanistic modeling of chromatography has been around in academia for decades and has gained increased support in pharmaceutical companies in recent years. Despite the large number of published successful applications, process development in the pharmaceutical industry today still does not fully benefit from a systematic mechanistic model-based approach. The hesitation on the part of industry to systematically apply mechanistic models can often be attributed to the absence of a general approach for determining if a model is qualified to support decision making in process development. In this work a Bayesian framework for the calibration and quality assessment of mechanistic chromatography models is introduced. Bayesian Markov Chain Monte Carlo is used to assess parameter uncertainty by generating samples from the parameter posterior distribution. Once the parameter posterior distribution has been estimated, it can be used to propagate the parameter uncertainty to model predictions, allowing a prediction-based uncertainty assessment of the model. The benefit of this uncertainty assessment is demonstrated using the example of a mechanistic model describing the separation of an antibody from its impurities on a strong cation exchanger. The mechanistic model was calibrated at moderate column load density and used to make extrapolations at high load conditions. Using the Bayesian framework, it could be shown that despite significant parameter uncertainty, the model can extrapolate beyond observed process conditions with high accuracy and is qualified to support process development. [ABSTRACT FROM AUTHOR]

Highlights • The effects of GC conditions on the response of PBDEs were explored with GC-ICP/MS. • CIC can be used for the tri- to hepta-BDEs under optimized GC conditions. • Heavier PBDEs are more severely affected by the matrix, resulting in inaccurate CIC. • The isomer of analytes could be used as a substitute to gain more accurate results. • The degradation of deca- BDE in GC was studied based on CIC. Abstract Compound-independent calibration (CIC) is a quantitative method that can quantify other compounds using a structure-independent compound as the calibrant. In this study, the potential and application of CIC method for the determination of polybrominated diphenyl ethers (PBDEs) using GC-ICP-MS was investigated. The effects of sample introduction conditions, the flow rate of the carrier gas, splitless delay time and the matrix of the complex sample on the response of 11 PBDEs compounds were explored. When pulsed splitless injection was used, the transmission efficiency of analytes from the inlet to the column can speed up with increasing injection temperature and pulse pressure, the elemental response of bromine of each analyte becomes closer. Under optimized chromatographic conditions, the response is independent of the compound can be found from the slope of the pure solution standard from tri- to hepta- brominated compounds (BDE 28 as reference) ranged from 0.968 to 1.001 (R2>0.998). The degradation ratio of BDE 209 in the GC-ICP/MS system was estimated by the CIC method to be 18.7%. During the determination of fish tissue sample, big difference of the elemental response ratio (BDE 28 as reference) was obtained range from 0.678 to 0.976. However, a similar elemental response was observed among isomers range from 0.990 to 1.056. This may mean that the isomers can be calibrated to each other in a complex matrix sample. The CIC method was validated by determination 3 PBDEs in NIST SRM 1947 frozen fish tissue certified reference materials using isomers as reference compounds. The recoveries of BDE 49 and BDE 66 were 105.7% and 88.1% by using BDE 47 as calibrants, and that of BDE 155 was 108.8% by using BDE 154 as calibrant. [ABSTRACT FROM AUTHOR]

Accurate measurement of molecular weight averages ( M ¯ n, M ¯ w, M ¯ z ) and molecular weight distributions (MWD) of polyether polyols by conventional SEC (size exclusion chromatography) is not as straightforward as it would appear. Conventional calibration with polystyrene (PS) standards can only provide PS apparent molecular weights which do not provide accurate estimates of polyol molecular weights. Using polyethylene oxide/polyethylene glycol (PEO/PEG) for molecular weight calibration could improve the accuracy, but the retention behavior of PEO/PEG is not stable in THF-based (tetrahydrofuran) SEC systems. In this work, two approaches for calibration curve conversion with narrow PS and polyol molecular weight standards were developed. Equations to convert PS-apparent molecular weight to polyol-apparent molecular weight were developed using both a rigorous mathematical analysis and graphical plot regression method. The conversion equations obtained by the two approaches were in good agreement. Factors influencing the conversion equation were investigated. It was concluded that the separation conditions such as column batch and operating temperature did not have significant impact on the conversion coefficients and a universal conversion equation could be obtained. With this conversion equation, more accurate estimates of molecular weight averages and MWDs for polyether polyols can be achieved from conventional PS-THF SEC calibration. Moreover, no additional experimentation is required to convert historical PS equivalent data to reasonably accurate molecular weight results. [ABSTRACT FROM AUTHOR]

Experimental: and theoretical studies were conducted to investigate low and non-linear responses in sub-micro molar-level suppressed ion chromatography with a hydroxide eluent. A calculated response was derived using experimentally determined detector effluent ion composition data and compared with measured experimental responses. The calibration curve was non-linear, and its slope varied considerably with different instrumental setups and operating conditions. The non-linearity of the solution conductivity response was determined by two acid-base equilibria of water and carbonic acid, and fluoride ion. By using eluent contaminated with para-toluene sulfonate at micro molar level, the non-linear response was greatly alleviated. [ABSTRACT FROM AUTHOR]

Quantitative High Performance Thin Layer Chromatography (HPTLC) requires the application of several standards to each plate, reducing the number of actual samples that can be analyzed in a single run. Using pure standard compounds and a selective detection method, the standards for quantitation can be applied besides – à côté – the chromatography area. This frees the sample application space to accommodate the maximal number of sample on each plate. Also, analysis time is spent exclusively on samples, drastically shortening the effective analysis time per sample and increasing sample throughput. Using this new calibration approach, the sample capacity of regular HPTLC methods can be increased or their scope be extended by an additional quantitative analysis. As a limitation, changes to the distribution of samples and standards within the plate as well as interferences from matrix compounds must be observed. We demonstrate the feasibility of this method by complementing an HPTLC method with a quantitative analysis of total anthocyanin content in colored wheat varieties. The quantitation was validated and compared to the conventional photometric analysis. As outcome, the additional photometric analysis could be replaced and rendered unnecessary, saving time, effort and equipment. This approach could also be employed to quantify highly retained substances, which are usually inaccessible for quantitative analysis. [ABSTRACT FROM AUTHOR]

A new approach for the calibration of SEC-light scattering (SEC-LS) setups is proposed, which requires solely the molar mass of a reference polymer. Neither the specific refractive index increment of the calibrant nor of the analyte is required. Comparison of the molar masses derived in different solvents for a large number of chemically different polymers shows that the new approach yields the same molar masses as if molar masses were derived using dn/dc to calibrate the light scattering setup. The approach therefore allows easier determination of molar masses by SEC-LS. [ABSTRACT FROM AUTHOR]

Monolithic silica in MonoSpin for solid-phase extraction of drugs from whole blood samples was developed to facilitate high-throughput analysis. Monolithic silica of various pore sizes and octadecyl contents were synthesized, and their effects on recovery rates were evaluated. The silica monolith M18-200 (20 μm through-pore size, 10.4 nm mesopore size, and 17.3% carbon content) achieved the best recovery of the target analytes in whole blood samples. The extraction proceeded with centrifugal force at 1000 rpm for 2 min, and the eluate was directly injected into the liquid chromatography–mass spectrometry system without any tedious steps such as evaporation of extraction solvents. Under the optimized condition, low detection limits of 0.5–2.0 ng mL −1 and calibration ranges up to 1000 ng mL −1 were obtained. The recoveries of the target drugs in the whole blood were 76–108% with relative standard deviation of less than 14.3%. These results indicate that the developed method based on monolithic silica is convenient, highly efficient, and applicable for detecting drugs in whole blood samples. [ABSTRACT FROM AUTHOR]

The rational strategy in the evaluation of analytical measurement uncertainty is to combine the “whole method” performance data, such as precision and recovery, with the uncertainty contributions from sources not adequately covered by those data. This paper highlights some common mistakes in evaluating the uncertainty when pursuing that strategy, as revealed in current chromatographic literature. The list of the uncertainty components usually taken into account is discussed first and fallacies with the LOD- and recovery uncertainties are noted. Close attention is paid to the uncertainty arising from a linear calibration normally used. It is demonstrated that following a well-known formula for the standard deviation of an analytical result obtained from a straight line calibration leads to double counting the precision contribution to the uncertainty budget. Furthermore, the precision component itself is often estimated improperly, based on the number of replicates taken from the precision assessment experiment. As a result, the relative uncertainty from linear calibration is overestimated in the budget and may become the largest contribution to the combined uncertainty, which is clearly shown with an example calculation based on the literature data. [ABSTRACT FROM AUTHOR]

The present paper is focused on the use of a vacuum ultraviolet absorption spectrometer (VUV) for gas chromatography (GC), within the context of flow modulated comprehensive two-dimensional gas chromatography (FM GC × GC). The features of the VUV detector were evaluated through the analysis of petrochemical and fatty acids samples. Besides responding in a predictable fashion via Beer’s law principles, the detector provides additional spectroscopic information for qualitative analysis. Virtually all chemical species absorb and have unique gas phase absorption features in the 120–240 nm wavelength range monitored. The VUV detector can acquire up to 90 full range absorption spectra per second, allowing its coupling with comprehensive two-dimensional gas chromatography. This recent form of detection can address specific limitations related to mass spectrometry ( e.g., identification of isobaric and isomeric species with very similar mass spectra or labile chemical compounds), and it is also able to deconvolute co-eluting peaks. Moreover, it is possible to exploit a pseudo-absolute quantitation of analytes based on pre-recorded absorption cross-sections for target analytes, without the need for traditional calibration. Using this and the other features of the detector, particular attention was devoted to the suitability of the FM GC × GC-VUV system toward qualitative and quantitative analysis of bio-diesel fuel and different kinds of fatty acids. Satisfactory results were obtained in terms of tailing factor (1.1), asymmetry factor (1.1), and similarity (average value 97%), for the FAMEs mixtures analysis. [ABSTRACT FROM AUTHOR]

Biomolecular and pharmaceutical downstream processing is dominated by chromatographic separation, which is associated with high product quality, low capacity and high costs. The separation can be optimized to minimize the costs while achieving a high purity. This paper presents an experimental validation of a discretized multi-level elution (DiME) trajectory, implemented on commercially available chromatography equipment. The tertiary protein separation of ribonuclease A, cytochrome C and lysozyme was used as a case study. A mechanistic model was calibrated using step and linear gradient experiments. The model was simulated together with the state sensitivities with respect to model parameters, which was used in the Levenberg–Marquardt algorithm to fit the model response to the experimental data. The model was used to solve the dynamic optimization problem of maximizing the yield of cytochrome C given a 95% purity requirement, 1000 s processing time and 50 salt concentration levels in the elution trajectory. The model was spatially discretized using finite volumes and temporally discretized using direct collocation. The corresponding non-linear programming problem was solved with IPOPT. Once the optimal salt trajectory was found it was experimentally implemented on an ÄKTA Pure using an OPC interface. The optimal trajectory was analyzed in-line by UV absorbance measurements and off-line by analysis of collected fractions. The results presented in this study show the successful experimental realization of DiME trajectories and how to use model calibration, optimization and control to realize DiME trajectories for any chromatography separation problem. [ABSTRACT FROM AUTHOR]

Degraded celluloses are becoming increasingly important as part of product streams coming from various biorefinery scenarios. Analysis of the molar mass distribution of such fractions is a challenge, since neither established methods for mono- or disaccharides nor common methods for polysaccharide characterization cover the intermediate oligomer range appropriately. Size exclusion chromatography (SEC) with multi-angle laser light scattering (MALLS), the standard approach for celluloses, suffers from decreased scattering intensities in the lower-molar mass range. The limitation in the low-molecular range can, in principle, be overcome by calibration, but calibration standards for such “short” celluloses are either not readily available or structurally remote and thus questionable. In this paper, we present the calibration of a SEC system— for the first time – with monodisperse cellooligomer standards up to about 3400 g mol −1 . These cellooligomers are “short-chain celluloses” and can be seen as the “true” standard compounds, by contrast to commonly used standards that are chemically different from cellulose, such as pullulan, dextran, polystyrene, or poly(methyl methacrylate). The calibration is compared against those commercial standards and correction factors are calculated. Calibrations with non-cellulose standards can now be adjusted to yield better fitting results, and data already available can be corrected retrospectively. [ABSTRACT FROM AUTHOR]

Performance reference compounds (PRCs) can be spiked into passive samplers prior to deployment. If the dissipation kinetics of PRCs from the sampler corresponds to analyte accumulation kinetics, then PRCs can be used to estimate in-situ sampling rates, which may vary depending on environmental conditions. Under controlled laboratory conditions, the effectiveness of PRC corrections on prediction accuracy of water concentrations were evaluated using nylon organic chemical integrative samplers (NOCIS). Results from PRC calibrations suggest that PRC elimination occurs faster under higher flow conditions; however, minimal differences were observed for PRC elimination between fast flow (9.3 cm/s) and slow flow (5.0 cm/s) conditions. Moreover, minimal differences were observed for PRC elimination from Dowex Optipore L-493; therefore, PRC corrections did not improve results for NOCIS configurations containing Dowex Optipore L-493. Regardless, results suggest that PRC corrections were beneficial for NOCIS configurations containing Oasis HLB; however, due to differences in flow dependencies of analyte sampling rates and PRC elimination rates across the investigated flow regimes, the use of multiple PRC corrections was necessary. As such, a “Best-Fit PRC” approach was utilized for Oasis HLB corrections using caffeine- 13 C 3 , DIA-d 5 , or no correction based on the relative flow dependencies of analytes and these PRCs. Although PRC corrections reduced the variability when in-situ conditions differed from laboratory calibrations ( e.g . static versus moderate flow), applying PRC corrections under similar flow conditions increases variability in estimated values. [ABSTRACT FROM AUTHOR]

Gas chromatography coupled with high resolution time of flight mass spectrometry (GC–HR-TOFMS) has gained popularity for the target and suspect analysis of complex samples. However, confident detection of target/suspect analytes in complex samples, such as produced water, remains a challenging task. Here we report on the development and validation of a two stage algorithm for the confident target and suspect analysis of produced water extracts. We performed both target and suspect analysis for 48 standards, which were a mixture of 28 aliphatic hydrocarbons and 20 alkylated phenols, in 3 produced water extracts. The two stage algorithm produces a chemical standard database of spectra, in the first stage, which is used for target and suspect analysis during the second stage. The first stage is carried out through five steps via an algorithm here referred to as unique ion extractor (UIE). During the first step the m / z values in the spectrum of a standard that do not belong to that standard are removed in order to produce a clean spectrum and then during the last step the cleaned spectrum is calibrated. The Dot-product algorithm, during the second stage, uses the cleaned and calibrated spectra of the standards for both target and suspect analysis. We performed the target analysis of 48 standards in all 3 samples via conventional methods, in order to validate the two stage algorithm. The two stage algorithm was demonstrated to be more robust, reliable, and less sensitive to the signal-to-noise ratio (S/N), when compared to the conventional method. The Dot-product algorithm showed lower potential in producing false positives compared to the conventional methods, when dealing with complex samples. We also evaluated the effect of the mass accuracy on the performances of Dot-product algorithm. Our results indicated the crucial importance of HR-MS data and the mass accuracy for confident suspect analysis in complex samples. [ABSTRACT FROM AUTHOR]

Among calibration approaches for organic compounds determination in complex matrices, external calibration, based in solutions of the analytes in solvent or in blank matrix extracts, is the most applied approach. Although matrix matched calibration (MMC) can compensates the matrix effects, it does not compensate low recovery results. In this way, standard addition (SA) and procedural standard calibration (PSC) are usual alternatives, despite they generate more sample and/or matrix blanks consumption need, extra sample preparations and higher time and costs. Thus, the goal of this work was to establish a fast and efficient calibration approach, the diluted standard addition calibration (DSAC), based on successive dilutions of a spiked blank sample. In order to evaluate the proposed approach, solvent calibration (SC), MMC, PSC and DSAC were applied to evaluate recovery results of grape blank samples spiked with 66 pesticides. Samples were extracted with the acetate QuEChERS method and the compounds determined by ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC–MS/MS). Results indicated that low recovery results for some pesticides were compensated by both PSC and DSAC approaches. Considering recoveries from 70 to 120% with RSD <20% as adequate, DSAC presented 83%, 98% and 100% of compounds meeting this criteria for the spiking levels 10, 50 and 100 μg kg −1 , respectively. PSC presented same results (83%, 98% and 100%), better than those obtained by MMC (79%, 95% and 97%) and by SC (62%, 70% and 79%). The DSAC strategy showed to be suitable for calibration of multiresidue determination methods, producing adequate results in terms of trueness and is easier and faster to perform than other approaches. [ABSTRACT FROM AUTHOR]

Environmental exposures often occur through short, pulsed events; therefore, the ability to accurately measure these toxicologically-relevant concentrations is important. Three different integrative passive sampler configurations were evaluated under different flow and pulsed exposure conditions for the measurement of current-use pesticides (n = 19), polyaromatic hydrocarbons (n = 10), and personal care products (n = 5) spanning a broad range of hydrophobicities (log Kow 1.5–7.6). Two modified POCIS-style samplers were investigated using macroporous nylon mesh membranes (35 μm pores) and two different sorbent materials (i.e. Oasis HLB and Dowex Optipore L-493). A recently developed design, the Sentinel Sampler (ABS Materials), utilizing Osorb media enclosed within stainless steel mesh (145 μm pores), was also investigated. Relatively high sampling rates ( Rs ) were achieved for all sampler configurations during the short eight-day exposure (4300–27 mL/d). Under flow conditions, median Rs were approximately 5–10 times higher for POCIS-style samplers and 27 times higher for Sentinel Samplers, as compared to static conditions. The ability of samplers to rapidly measure hydrophobic contaminants may be a trade off with increased flow dependence. Analyte accumulation was integrative under pulsed and continuous exposures for POCIS-style samplers with mean difference between treatments of 11% and 33%; however, accumulation into Sentinel Samplers was more variable. Collectively, results show that reducing membrane limitations allows for rapid, integrative accumulation of a broad range of analytes even under pulsed exposures. As such, these sampler designs may be suitable for monitoring environmental substances that have short aquatic half-lives. [ABSTRACT FROM AUTHOR]

A novel method for rapid, quantitative determination of trace permanent gases and carbon dioxide in ultra-high purity ammonia by dual-channel two-dimensional GC-PDHID is presented. An improved matrix back-flush-to-vent approach combining back-flush column switching technique with auxiliary NaHSO 4 ammonia trap is described. The NaHSO 4 trap prevents traces of ammonia from entering the analytical column and is shown not to affect the impurity content of the sample. The approach allows shortening the analysis time and increasing the amount of measurements without extensive maintenance of the GC-system. The performance of the configuration has been evaluated utilizing ammonia- and helium-based calibration standards. The method has been applied for the analysis of 99.9999+% ammonia purified by high-pressure distillation at the production site. [ABSTRACT FROM AUTHOR]

In this contribution, a multiplicative effects model for generalized multiple-internal-standard method (MEM GMIS ) was proposed to solve the signal instability problem of LC–MS over time. MEM GMIS model seamlessly integrates the multiple-internal-standard strategy with multivariate calibration method, and takes full use of all the information carried by multiple internal standards during the quantification of target analytes. Unlike the existing methods based on multiple internal standards, MEM GMIS does not require selecting an optimal internal standard for the quantification of a specific analyte from multiple internal standards used. MEM GMIS was applied to a proof-of-concept model system: the simultaneous quantitative analysis of five edible artificial colorants in two kinds of cocktail drinks. Experimental results demonstrated that MEM GMIS models established on LC–MS data of calibration samples prepared with ultrapure water could provide quite satisfactory concentration predictions for colorants in cocktail samples from their LC–MS data measured 10 days after the LC–MS analysis of the calibration samples. The average relative prediction errors of MEM GMIS models did not exceed 6.0%, considerably better than the corresponding values of commonly used univariate calibration models combined with multiple internal standards. The advantages of good performance and simple implementation render MEM GMIS model a promising alternative tool in quantitative LC–MS assays. [ABSTRACT FROM AUTHOR]

Liquid chromatography–mass spectrometry (LC–MS) is now a main stream technique for large-scale metabolic phenotyping to obtain a better understanding of genomic functions. However, repeatability is still an essential issue for the LC–MS based methods, and convincing strategies for long time analysis are urgently required. Our former reported pseudotargeted method which combines nontargeted and targeted analyses, is proved to be a practical approach with high-quality and information-rich data. In this study, we developed a comprehensive strategy based on the pseudotargeted analysis by integrating blank-wash, pooled quality control (QC) sample, and post-calibration for the large-scale metabolomics study. The performance of strategy was optimized from both pre- and post-acquisition sections including the selection of QC samples, insertion frequency of QC samples, and post-calibration methods. These results imply that the pseudotargeted method is rather stable and suitable for large-scale study of metabolic profiling. As a proof of concept, the proposed strategy was applied to the combination of 3 independent batches within a time span of 5 weeks, and generated about 54% of the features with coefficient of variations (CV) below 15%. Moreover, the stability and maximal capability of a single analytical batch could be extended to at least 282 injections (about 110 h) while still providing excellent stability, the CV of 63% metabolic features was less than 15%. Taken together, the improved repeatability of our strategy provides a reliable protocol for large-scale metabolomics studies. [ABSTRACT FROM AUTHOR]

A sensitive, accurate and reliable multi-class GC-MS/MS assay protocol for quantification and confirmation of 200 common agricultural pesticides in honey was developed and validated according to EU guidelines. A modified extraction procedure, based on QuEChERS method (quick, easy, cheap, effective, rugged and safe) was employed. Mass spectrophotometric conditions were individually optimized for each analyte to achieve maximum sensitivity and selectivity in MRM mode. The use of at least two reactions for each compound allowed simultaneous identification and quantification in a single run. The pesticides under investigation were separated in less than 31 min using the ultra-inert capillary column (DB-35MS). For all analytes, neat standard calibration curves in conjunction with correction for matrix effect were successfully employed. The detection limits of the assay ranged from 1.00 to 3.00 ng mL-1 for the studied pesticides. The developed assay was linear over concentration range of 10.00-500.00 ng mL-1, with correlation coefficient of more than 0.996. At the LOQ, 81% of the studied pesticides were efficiently recovered in the range of 70.00-120.00%, with CV% less than 15.00% while 99.3% compounds had mean percentage recovery of 60.00-140.00%, with CV% less than 21.00% (N = 18, over three different days). The proposed assay was successfully applied for the analysis of the studied pesticide residues in one PT sample and 64 commercial honey samples collected over 1 year from different districts around Egypt. Results revealed that only one honey sample out of the 64 analyzed samples was contaminated with tau-Fluvalinate (10.00 μg kg-1). This wide scope assay protocol is applicable for monitoring pesticide residues in honey by national regulatory authorities and accredited labs; that should help ensure safety of such widely used product. [ABSTRACT FROM AUTHOR]

We describe modified gas chromatography electron-impact/triple-quadrupole mass spectrometry (GC–EI/MS/MS) utilizing a newly developed hydrogen-injected self-cleaning ion source and modified 9 mm extractor lens. This instrument, with optimized parameters, achieves quantitative separation of 62 polycyclic aromatic hydrocarbons (PAHs). Existing methods historically limited rigorous identification and quantification to a small subset, such as the 16 PAHs the US EPA has defined as priority pollutants. Without the critical source and extractor lens modifications, the off-the-shelf GC–EI/MS/MS system was unsuitable for complex PAH analysis. Separations were enhanced by increased gas flow, a complex GC temperature profile incorporating multiple isothermal periods, specific ramp rates, and a PAH-optimized column. Typical determinations with our refined GC–EI/MS/MS have a large linear range of 1–10,000 pg μl −1 and detection limits of <2 pg μl −1 . Included in the 62 PAHs, multiple-reaction-monitoring (MRM) mode enabled GC-EI/MS/MS identification and quantitation of several constituents of the MW 302 PAH isomers. Using calibration standards, values determined were within 5% of true values over many months. Standard curve r 2 values were typically >0.998, exceptional for compounds which are archetypally difficult. With this method benzo[a]fluorene, benzo[b]fluorene, benzo[c]fluorene were fully separated as was benzo[b]fluoranthene, benzo[k]fluoranthene, and benzo[j]fluoranthene. Chrysene and triphenylene, were sufficiently separated to allow accurate quantitation. Mean limits of detection (LODs) across all PAHs were 1.02 ± 0.84 pg μl −1 with indeno[1,2,3-c,d] pyrene having the lowest LOD at 0.26 pg μl −1 and only two analytes above 2.0 pg μl −1 ; acenaphthalene (2.33 pg μl −1 ) and dibenzo[a,e]pyrene (6.44 pg μl −1 ). [ABSTRACT FROM AUTHOR]

A capillary electrophoresis–tandem mass spectrometry (CE–MS/MS) method for the simultaneous assessment of nine biogenic amines (spermine, spermidine, putrescine, cadaverine, histamine, phenylethylamine, tryptamine, tyramine, and urocanic acid) in commercial samples of beer and wine is introduced. The samples were submitted to a simple clean-up step with poly(vinylpolypyrrolidone) followed by filtration. Electrophoretic separation in a polyvinyl alcohol (PVA)-coated capillary using 0.5 mol L −1 acetic acid (pH 2.5) as background electrolyte and detection by electrospray-tandem mass spectrometry was employed. The range of the correlation coefficients of the calibration curves of the analyzed compounds was 0.996–0.999, and the limits of detection and limits of quantification were in the range of 1–2 μg L −1 and 3–8 μg L −1 , respectively. The recovery values for samples spiked at three concentration levels (0.2, 0.5, and 1.0 mg L −1 ) ranged from 87 to 113% with standard deviation not greater than 5.8%. The use of a PVA-coated silica capillary allows suppressing the electroosmotic flow and, consequently, increasing of the separation efficiency. The method was successfully used to determine biogenic amines in commercial samples of beer and wine. [ABSTRACT FROM AUTHOR]

SPME is extremely sensitive to experimental parameters affecting liquid–gas and gas–solid distribution coefficients. Our aims were to measure the weights of these factors and to design a multivariate strategy based on the addition of a pool of internal standards, to minimize matrix effects. Synthetic but real-like wines containing selected analytes and variable amounts of ethanol, non-volatile constituents and major volatile compounds were prepared following a factorial design. The ANOVA study revealed that even using a strong matrix dilution, matrix effects are important and additive with non-significant interaction effects and that it is the presence of major volatile constituents the most dominant factor. A single internal standard provided a robust calibration for 15 out of 47 analytes. Then, two different multivariate calibration strategies based on Partial Least Square Regression were run in order to build calibration functions based on 13 different internal standards able to cope with matrix effects. The first one is based in the calculation of Multivariate Internal Standards (MIS), linear combinations of the normalized signals of the 13 internal standards, which provide the expected area of a given unit of analyte present in each sample. The second strategy is a direct calibration relating concentration to the 13 relative areas measured in each sample for each analyte. Overall, 47 different compounds can be reliably quantified in a single fully automated method with overall uncertainties better than 15%. [ABSTRACT FROM AUTHOR]

Accurate characterization of the molar mass and size of polysaccharides is an ongoing challenge, oftentimes due to architectural diversity but also to the broad molar mass ( M ) range over which a single polysaccharide can exist and to the ultra-high M of many polysaccharides. Because of the latter, many of these biomacromolecules experience on-column, flow-induced degradation during analysis by size-exclusion and, even, hydrodynamic chromatography (SEC and HDC, respectively). The necessity for gentler fractionation methods has, to date, been addressed employing asymmetric flow field-flow fractionation (AF4). Here, we introduce the coupling of hollow-fiber flow field-flow fractionation (HF5) to multi-angle static light scattering (MALS) and differential refractometry (DRI) detection for the analysis of polysaccharides. In HF5, less stresses are placed on the macromolecules during separation than in SEC or HDC, and HF5 can offer a higher sensitivity, with less propensity for system overloading and analyte aggregation, than generally found in AF4. The coupling to MALS and DRI affords the determination of absolute, calibration-curve-independent molar mass averages and dispersities. Results from the present HF5/MALS/DRI experiments with dextrans, pullulans, and larch arabinogalactan were augmented with hydrodynamic radius ( R H ) measurements from off-line quasi-elastic light scattering (QELS) and by R H distribution calculations and fractogram simulations obtained via a finite element analysis implementation of field-flow fractionation theory by commercially available software. As part of this study, we have investigated analyte recovery in HF5 and also possible reasons for discrepancies between calculated and simulated results vis-à-vis experimentally determined data. [ABSTRACT FROM AUTHOR]

A method using direct sample introduction (DSI) coupled to gas chromatography–mass spectrometry (GC–MS) is developed for the determination of six phthalate esters (dimethyl, diethyl, dibutyl, butylbenzyl, diethylhexyl and dioctyl phthalate) in cleaning products. The different variables involved in the DSI step, including venting time and temperature, vaporisation time and temperature, injector heating temperature and gas flow rate and pressure, were evaluated and optimised using Taguchi orthogonal arrays. The proposed method, using calibration against methanolic standards, showed good linearity in the 0.05–15 μg g −1 range and good repeatability, with RSD values ranging from 3.5% to 5.7%. Quantification limits between 0.010 and 0.041 μg g −1 , depending on the compound, were attained, while recovery assays provided values from 83% to 115%. Twenty-seven cleaning products were analysed using the DSI–GC–MS method, being four phthalates (dimethyl, diethyl, dibutyl and diethylhexyl phthalate) found in fourteen of them at concentration levels in the 0.1–21 μg g −1 range. Compared with the most common GC injection technique, which uses the split/splitless injector, the proposed DSI procedure provided larger peak areas and lower detection limits, as result of the greater injected volume and reduction in noise. [ABSTRACT FROM AUTHOR]

An online solid-phase microextraction coupled liquid chromatography-electrospray ionization-ion trap mass spectrometry was developed for the analysis of trace R - and S -4-phenyl-2-butanol ( R - and S -pbol) in salt rich cell culture of Saccharomyces cerevisiae catalyzed stereoselective reduction of 4-pheny-2-butanone (pbone). A Supel-Q PLOT capillary column was used for the extraction and deionized distilled water was used as the extraction mobile phase. The extraction flow rate and extraction time were at 0.1 mL min −1 and 0.95 min, respectively. The three target analytes, pbone, R -pbol, and S -4-pbol, were desorbed and eluted by the mobile phase of water/methanol/isopropanol (55/25/20, v/v/v) with a flow rate of 0.5 mL min −1 and analyzed by a chiral column. The mass spectrometric detection of the three target analytes was in positive ion mode with the signal [M+Na] + . The matrix-matched external standard calibration curves with linear concentration range between 0 and 50 μg mL −1 were used for quantitative analysis. The linear regression correlation coefficients ( r 2 ) of the standard calibration curves were between 0.9950 and 0.9961. The yeast mediated reduction was performed with a recation culture of yeast incubation culture/glycerol (70/30, v/v) for 4 days. This biotransformation possessed 82.3% yield and 92.9% S -enantomeric excess. The limit of detection (LOD)/limit of quantification (LOQ) for pbone, R -pbol, and S -pbol was 0.02/0.067, 0.01/0.033, and 0.01/0.033 μg mL −1 , respectively. The intra-day and inter-day precisions from repeated measurements were 10.8–21.1% and 11.6–18.7%, respectively. The analysis accuracy from spike recovery was 84–91%. [ABSTRACT FROM AUTHOR]

Models to predict the total antioxidant capacity (TAC) of rooibos tea infusions from their chromatographic fingerprints and peak table data (content of individual phenolic compounds), obtained using HPLC with diode array detection, were developed in order to identify potential antioxidant markers. Peak table data included the content of 12 compounds, namely phenylpyruvic acid-2- O -glucoside, aspalathin, nothofagin, isoorientin, orientin, ferulic acid, quercetin-3- O -robinobioside, vitexin, hyperoside, rutin, isovitexin and isoquercitrin. The TAC values, measured using the oxygen radical absorbance capacity (ORAC) and DPPH radical scavenging assays, could be predicted from the peak table data or the chromatographic fingerprints (prediction errors 9–12%) using partial least squares (PLS) regression. Prediction models created from samples of only two production years could additionally be used to predict the TAC of samples from another production year (prediction errors < 13%) indicating the robustness of the models in a quality control environment. Furthermore, the uninformative variable elimination (UVE)-PLS method was used to identify potential antioxidant markers for rooibos infusions. All individual phenolic compounds that were quantified were selected as informative variables, except vitexin, while UVE-PLS models developed from chromatographic fingerprints indicated additional antioxidant markers, namely ( S )-eriodictyol-6- C -glucoside, ( R )-eriodictyol-6- C -glucoside, aspalalinin and two unidentified compounds. The potential antioxidant markers should be validated prior to use in quality control of rooibos tea. [ABSTRACT FROM AUTHOR]

In this work, an attractive chemometrics-enhanced high performance liquid chromatography-diode array detection (HPLC-DAD) strategy was proposed for simultaneous and fast determination of eight co-eluted compounds including gallic acid, caffeine and six catechins in ten kinds of Chinese teas by using second-order calibration method based on alternating trilinear decomposition (ATLD) algorithm. This new strategy proved to be a useful tool for handling the co-eluted peaks, uncalibrated interferences and baseline drifts existing in the process of chromatographic separation, which benefited from the “second-order advantages”, making the determination of gallic acid, caffeine and six catechins in tea infusions within 8 min under a simple mobile phase condition. The average recoveries of the analytes on two selected tea samples ranged from 91.7 to 103.1% with standard deviations (SD) ranged from 1.9 to 11.9%. Figures of merit including sensitivity (SEN), selectivity (SEL), root-mean-square error of prediction (RMSEP) and limit of detection (LOD) have been calculated to validate the accuracy of the proposed method. To further confirm the reliability of the method, a multiple reaction monitoring (MRM) method based on LC–MS/MS was employed for comparison and the obtained results of both methods were consistent with each other. Furthermore, as a universal strategy, this new proposed analytical method was applied for the determination of gallic acid, caffeine and catechins in several other kinds of Chinese teas, including different levels and varieties. Finally, based on the quantitative results, principal component analysis (PCA) was used to conduct a cluster analysis for these Chinese teas. The green tea, Oolong tea and Pu-erh raw tea samples were classified successfully. All results demonstrated that the proposed method is accurate, sensitive, fast, universal and ideal for the rapid, routine analysis and discrimination of gallic acid, caffeine and catechins in Chinese tea samples. [ABSTRACT FROM AUTHOR]

This work demonstrates a novel method for rapid determination of total solid content in viscous liquid (polymer-enriched) samples. The method is based multiple headspace extraction gas chromatography (MHE-GC) on a headspace vial at a temperature above boiling point of water. Thus, the trend of water loss from the tested liquid due to evaporation can be followed. With the limited MHE-GC testing (e.g., 5 extractions) and a one-point calibration procedure (i.e., recording the weight difference before and after analysis), the total amount of water in the sample can be determined, from which the total solid contents in the liquid can be calculated. A number of black liquors were analyzed by the new method which yielded results that closely matched those of the reference method; i.e., the results of these two methods differed by no more than 2.3%. Compared with the reference method, the MHE-GC method is much simpler and more practical. Therefore, it is suitable for the rapid determination of the solid content in many polymer-containing liquid samples. [ABSTRACT FROM AUTHOR]

We report here a new analytical method for the simultaneous determination of seven haloacetonitriles (HANs) in drinking water by coupling salt-assisted dispersive liquid-liquid microextraction (SADLLME) with programmed temperature vaporizer-gas chromatography-mass spectrometry (PTV-GC-MS). The newly developed method involves the dispersion of the extractant in aqueous sample by addition of a few grams of salt and no dispersion liquid was required as compared to the traditional DLLME methods. The extractant (CH2Cl2, 50µL) and the salt (Na2SO4, 2.4g) were successively added to water (8mL) in a conical centrifuge tube that was shaken for 1min and centrifuged (3500rpm, 3min). The aliquot of sedimented phase (4µL) was then directly injected into the PTV-GC-MS system. The limits of detection and quantification for the HANs were 0.4-13.2ngL-1 and 1.2-43.9ngL-1, respectively. The calibration curves showed good linearity (r²≥0.9904) over 3 orders of magnitude. The repeatability of the method was investigated by evaluating the intra- and inter-day precisions. The relative standard deviations (RSDs) obtained were lower than 10.2% and 7.8% at low and high concentration levels. The relative recoveries ranged from 79.3% to 105.1%. The developed methodology was applied for the analysis of seven HANs in several drinking water samples in coastal and inland cities of China. It was demonstrated to be a simple, sensible, reproducible and environment friendly method for the determination of trace HANs in drinking water samples. [ABSTRACT FROM AUTHOR]

Highlights: [•] The precision of the final or reportable result can be optimised. [•] An equation is developed to optimise also the format of calibration. [•] Optimisation is possible by varying the number of determinations. [•] Reliable variances are the basis for optimisation. [•] Obtaining reliable variance contributions is the aim of precision studies. [ABSTRACT FROM AUTHOR]

• The readily available reference materials, eicosane and NIST 1475, was used to develop a two-point temperature calibration methodology. • Robustness was verified with 3000 injections of LLDPE-M in 8-year study with six instruments located in different countries. • A two-point comonomer content calibration with homopolymer PE and hexacontane was found to be sufficient in a range of 0-8.5mol%. Comonomer content distribution (CCD), also commonly known as chemical composition distribution (CCD) and short chain branching distribution (SCBD), describes the variation of short chain branching composition between individual polymer chains in polyolefin materials. It is of particular importance for controlling polyolefin performance. Crystallization-based separation methods have evolved over the past four decades aiming at resolution, speed, precision, and accuracy. Two of the commonly used techniques are Crystallization Elution Fractionation (CEF) and Temperature Rising Elution Fractionation (TREF), where polymer chains are physically separated along the column or on the surface of the support based on their crystallinity, respectively. CEF analysis takes much less time than TREF. There is a critical need for precise temperature calibrations for data repeatability. This report demonstrates a novel CEF methodology using a two-point technique to consistently and conveniently calibrate the comonomer composition and column temperature. This column temperature calibration methodology was adopted in a study by tracking the reproducibility over a period of 8 years, using multiple instruments located in different laboratories and in different geographies. The results exhibited superior repeatability, with less than 0.3% of the relative error calculated from 3000 data points of the eluting peak temperature, thus demonstrating this as a robust method for industrial labs that require good quality controls. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new method was proposed for maintaining the long term stability of LC–MS/MS calibration models. [•] The method can obtain accurate quantitative results even if variation occurs in sensitivity of LC–MS. [•] It offers significant advantages over other methods in terms of performance and implementation simplicity. [Copyright &y& Elsevier]

Highlights: [•] Stir bar sorptive extraction is used as a passive sampler in water (passive SBSE). [•] Passive SBSE is calibrated for 18 pesticides in a flow-through system. [•] Accurate sampling rates and short lag-phases are determined for all pesticides. [•] We observe the impact of flow velocity on the uptake of 5 hydrophobic pesticides. [•] Fenitrothion-d6 is shown as a promising performance reference compound candidate [Copyright &y& Elsevier]

Highlights: [•] Development of a simple and rapid sample preparation procedure. [•] Determination of 96 veterinary drugs among multi chemical classes selected. [•] Thorough method validation including matrix matched calibration. [•] Application in different samples of Distillers Dried Grains with Solubles (DDGS). [ABSTRACT FROM AUTHOR]

Highlights: [•] A GC method was developed to detect the viscosity of concentrated black liquors. [•] Methanol is used as the tracer and its release profile is measured by MHE-GC. [•] Two correlation approaches were established for the calibration method. [•] The presented method is simple and practical for black liquor viscosity testing. [Copyright &y& Elsevier]

Highlights: [•] cis/trans-Isomers of resveratrol, piceatannol and oxyresveratrol are determined by SBSE-GC–MS. [•] A new and easy to perform way to obtain the cis-isomers is given. [•] Analysis of wine samples is carried out using aqueous standards for calibration. [Copyright &y& Elsevier]

Highlights: [•] A separation of nine natural and synthetic estrogens by HPLC–DAD/FD is proposed. [•] A HF-LPME method is suggested for the extraction of these estrogens from milk. [•] Deproteinization and parameters affecting HF-LPME were studied and optimized. [•] Calibration of the whole method was done for skimmed, semi-skimmed and whole milk. [•] A precision and accuracy study for further validation was made for each matrix. [Copyright &y& Elsevier]

Highlights: [•] Development of a simple and rapid sample preparation procedure. [•] Multi chemical classes/groups selected. [•] Thorough method validation including matrix matched and standard addition calibration approaches. [•] Application in different feed matrices. [Copyright &y& Elsevier]

Highlights: [•] GC×GC techniques applied to the analysis of sesquiterpene derivatives. [•] Comparative analysis of vetiver oils of different origins by means of GC×GC–MS. [•] Quantitation of vetiver oil constituents by internal calibration using GC×GC-FID. [•] Influence of the injection mode on the determined chemical composition. [ABSTRACT FROM AUTHOR]