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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]

A rapid and quantitative analytical method for volatile chlorinated hydrocarbons and benzene, such as chloroethylene, dichloromethane, and carbon tetrachloride, in soil samples was developed using a needle-type extraction device packed with activated carbon-based adsorbents. The soil sample of 10 g was placed in a glass cartridge and fixed with quartz wool to make sure not to move during the extraction process. After the internal standard solution was spiked into the soil sample, the cartridge was sealed with a polytetrafluoroethylene adapter, and the needle extraction device was used to collect the headspace gas. Analytes were purged from the soil sample and collected on the adsorbent, while pure nitrogen gas was introduced to the soil sample during the sample collection. The sampling time was approximately 10 min for 100 mL of gas sampling. After the sampling process, the extraction needle was directly inserted into a heated injection port of gas chromatography equipped with flame ionization detector (GC-FID) or that hyphenated to mass spectrometry (GC-MS). The extracted VOCs were thermally desorbed and simultaneously introduced to a GC capillary column for subsequent separation and determination. The limit of detection and limit of quantification of all the examined analytes was less than 20 and 60 ng/10 g soil in GC-FID and less than 2.5 and 7.5 ng/10 g soil in the case of GC-MS. Linear calibration curves were obtained up to 10 μg/10 g soil for all the analytes. The relative standard deviations of the ratio of analyte peak area and internal standard peak area were less than 10%. The recovery and sensitivity of analytes confirmed in the proposed method were compared with that obtained with a standard method conventionally employed., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence this work., (Copyright © 2022. Published by Elsevier B.V.)

There are several potential advantages of using experimental design-based retention modeling for chromatographic method development. Most importantly, through the model-delivered systematic understanding (Design Spaces), users can benefit from increased method consistency, flexibility and robustness that can efficiently be achieved at lesser amount of development time. As a result, modeling tools have always been great supplementary assets and welcomed by both the pharmaceutical industry and the regulatory authorities. Most recently published chapters of ICH however - Q2(R2) and Q14 (both currently drafts) - evidence a further paradigm shift, specifying the elements of model-based development strategies in the so-called "enhanced approach". The main aim of this study was to investigate the impact of stationary phase chemistries on chromatographic method performance in the application example of ezetimibe and its related substances. A commercial modeling software package (DryLab®) was used to outline three-dimensional experimental design frameworks and acquire model Design Spaces (DSs) of 9 tested columns. This was done by performing 12 input calibration experiments per column, systematically changing critical method parameters (CMPs) as variables such as the gradient time (tG), temperature (T) and the ternary composition (tC) of the mobile phase. The constructed models allowed studying retention behaviors of selected analytes within each separation systems. In the first part of our work, we performed single optimizations for all nine stationary phases with substantially different surface modifications based on their highest achievable critical resolution values. For these optimum points in silico robustness testing was performed, clearly showing a change of CMPs, depending on the column, and specified optimum setpoint. In the second part of our work, we simultaneously compared the three-dimensional virtual separation models to identify all method parameter combinations that could provide at least baseline separation (R s, crit. >1.50). These overlapping areas between the models described a common method operational design region (MODR) where columns were considered completely interchangeable - in terms of their baseline resolving capability - regardless of their exact physicochemical properties. A final optimized, column-independent working point within the common MODR was selected for verification. Indeed, experimental chromatograms showed excellent agreement with the model; all columns in the common condition were able to yield critical resolution values higher than 2.0, only their retentivity (elution window of peaks) was found different in some cases. Our results underline that a profound understanding of the separation process is of utmost importance andthat in some cases, adequate selectivity is achievable on various stationary phases., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

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]

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]

Ion exchange chromatography (IEC) is one of the most widely-used techniques for protein separation and has been characterized by mechanistic models. However, the time-consuming and cumbersome model calibration hinders the application of mechanistic models for process development. A new methodology called "parameter-by-parameter method (PbP)" was proposed with mechanistic derivations of the steric mass action (SMA) model of IEC. The protocol includes four steps: (1) first linear regression (LR1) for characteristic charge; (2) second linear regression (LR2) for equilibrium coefficient; (3) linear approximation (LA) for shielding factor; (4) inverse method (IM) for kinetic coefficient. Four SMA parameters could be one-by-one determined in sequence, reducing the number of unknown parameters per species from four to one, and predicting almost consistent retention. Numerical single-component experiments were investigated firstly, and the PbP method showed excellent agreement between experiments and simulations. The effects of loadings on the PbP and Yamamoto methods were compared. It was found that the PbP method had higher accuracy and robustness than the Yamamoto method. Moreover, a five-experiment strategy was suggested to implement the PbP method, which is straightforward to reduce the cost of calibration experiments. Finally, a real-world multi-component separation was challenged and further confirmed the feasibility of the PbP method. In general, the proposed method can not only reliably estimate the SMA parameters with comprehensive physical understanding but also accurately predict retention over a wide range of loading conditions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The measurement of VOSCs in complex matrices is challenging due to their volatile and reactive nature. A straightforward method using headspace chromatography was developed for routine analyses of organosulfur compounds in a high saline liquid matrix with a pH of 8.4. Direct sample acidification with a 1M acetate buffer (pH 3.6) showed an increased response for methanethiol, ethanethiol, propanethiol, dimethyl sulfide, dimethyl disulfide and diethyl disulfide. A good quadratic fit (R 2 <0.995) was obtained for each compound over a calibration range of 5 µM-S until 125 µM-S (µmol sulfur/L). Gas standards were measured using the same chromatographic conditions over a calibration range of 0.08 µM-S until 1.85 µM-S (R 2 <0.999). Gas standards could also be used to calibrate the liquid phase with a response ratio of 105.2% for ET, 107% for DMS, 105.7% for PT, 108.9% for DMDS and 106% for DEDS. This alternative calibration strategy reduced the preparation time and does not rely on liquid standards, which were unstable over time. This method was used to determine Henry constants for the organosulfur compounds both in demineralized water and the high saline liquid matrix and to analyze samples from a bio electrochemical experiment that treated methanethiol. This new method allows for routine analysis of samples originating from natural gas desulfurization plants and can potentially also be used to analyze organosulfur compounds in other complex waste streams., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)

An enzyme-assisted extraction and an ion pairing reversed phase chromatography (IP-RPC) coupled to inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) method were established for the simultaneous analysis of five selenium species in rice: selenious acid (SeIV), selenic acid (SeVI), selenocystine (SeCys 2 ), methylselenocysteine (SeMeCys) and selenomethionine (SeMet). Optimal extraction efficiencies were obtained by using 15 mg protease XIV, water bath temperature of 45°C, pH of 6.5 and incubation of six hours. The total extracted Se species account for 92.5-109.3 % of the total Se in rice. The instrumental limits of detection for five selenium species ranged from 0.04 to 0.12 ng Se g -1 . Spike recovery experiments performed on rice samples were in the range of 96.1-102.9 % for all analytes except for SeCys 2 (66.1-77.1 %). A consistency of Se elemental response was observed among Se species analyzed in this study as the ratio of linear equation slope ranged from 1.020 to 1.036 (SeIV as reference) in rice matrix. The developed compound-independent calibration method was applied to detect Se species in eleven rice samples from China. Both selenium-enriched rice and regular rice were predominated with SeMet, accounting for ∼89.4 % of total selenium., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In this work, a simple and effective strategy for the determination of 12 active compounds of Atractylodes macrocephala Koidz. (AM) was proposed by using high performance liquid chromatography-diode array detection (HPLC-DAD) combined with alternating trilinear decomposition (ATLD) algorithm. Utilizing the "second-order advantage", three common problems in HPLC could be resolved, namely baseline drifts, peak overlaps, and unknown interferences. 12 compounds were rapidly eluted within 12.5 min, and the average spiked recoveries were 80.8-109.9%. The figures of merit reflected the feasibility of the proposed method. Compared with the results of the traditional univariate calibration method based on HPLC-UV technique, the proposed strategy further verified the reliability and simplicity of the mathematical separation. On this basis, partial least squares-discriminant analysis (PLS-DA) was applied to discriminate 113 AM samples from different geographical origins, and variable importance in projection (VIP) was used to further screen the main differential components that affect the regional division of AM. A series of results show that the AM samples from the three regions have obviously different clustering trends. Overall, the strategy is expected to provide a scientific basis for the modern research of medicinal materials, and it is also conducive to the clinical use and market supervision of AM., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

• 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: [•] 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]

Abstract: High-purity carbon monoxide (CO) gas as a certified reference material (CRM) was analyzed using a micro gas chromatograph (micro-GC) with a micro thermal conductivity detector. The main reason to select the micro-GC was its compact size to provide a safe experimental environment. Thus, both the CO gas cylinder and the micro-GC were placed inside a draft shield with a limited small space. Peaks of several impurities were found in chromatograms of the micro-GC. The main impurities in the CO gas were helium, hydrogen, oxygen, nitrogen and carbon dioxide. It was found that helium was the impurity of the highest concentration. High-accuracy calibration gas mixtures were used to construct calibration lines for the micro-GC. The mixtures were precisely prepared by the gravimetric blending method. Calibration lines had enough linearity and accuracy for quantitative analyses of the impurities. The values of detection limit of the impurities were 0.7–4μmol/mol. The purity of the high-purity CO gas was around 99.996%, which was the value estimated from the sum of the concentrations of the impurities. [Copyright &y& Elsevier]

Abstract: A simple method for establishing calibration curves with sorbent-filled thermal desorption tubes has been demonstrated for nitroaromatic and nitramine vapor samples using a thermal desorption system with a cooled inlet system (TDS–CIS), which was coupled to a gas chromatograph (GC) with an electron capture detector (ECD). The method relies upon the direct liquid deposition of standard solutions onto the glass frit at the head of sorbent-filled thermal desorption tubes. Linear calibration results and ideal system conditions for the TDS–CIS–GC–ECD were established for mixtures containing both cyclotrimethylenetrinitramine, a.k.a. RDX, and 2,4,6-trinitrotoluene (TNT). Because of the chemical characteristics of RDX, a higher TDS–CIS flow rate relative to the optimized approach for TNT was required for efficient RDX desorption. Simultaneous quantitation of TNT and RDX using the direct liquid deposition method with optimized instrumentation parameters for RDX were compared to results from a standard split/splitless GC inlet and a CIS. [Copyright &y& Elsevier]

Abstract: We performed a comprehensive study to assess the fit for purpose of four chromatographic conditions for the determination of six groups of marine lipophilic toxins (okadaic acid and dinophysistoxins, pectenotoxins, azaspiracids, yessotoxins, gymnodimine and spirolides) by LC–MS/MS to select the most suitable conditions as stated by the European Union Reference Laboratory for Marine Biotoxins (EURLMB). For every case, the elution gradient has been optimized to achieve a total run-time cycle of 12min. We performed a single-laboratory validation for the analysis of three relevant matrices for the seafood aquaculture industry (mussels, pacific oysters and clams), and for sea urchins for which no data about lipophilic toxins have been reported before. Moreover, we have compared the method performance under alkaline conditions using two quantification strategies: the external standard calibration (EXS) and the matrix-matched standard calibration (MMS). Alkaline conditions were the only scenario that allowed detection windows with polarity switching in a 3200 QTrap mass spectrometer, thus the analysis of all toxins can be accomplished in a single run, increasing sample throughput. The limits of quantification under alkaline conditions met the validation requirements established by the EURLMB for all toxins and matrices, while the remaining conditions failed in some cases. The accuracy of the method and the matrix effects where generally dependent on the mobile phases and the seafood species. The MMS had a moderate positive impact on method accuracy for crude extracts, but it showed poor trueness for seafood species other than mussels when analyzing hydrolyzed extracts. Alkaline conditions with EXS and recovery correction for OA were selected as the most proper conditions in the context of our laboratory. This comparative study can help other laboratories to choose the best conditions for the implementation of LC–MS/MS according to their own necessities. [Copyright &y& Elsevier]

Abstract: A method is described for characterization of sulfur compounds in unaged and aged whisky. The method is based on full evaporation dynamic headspace (FEDHS) of 100μL of whisky samples followed by selectable one-dimensional (1D) or two-dimensional (2D) retention-time-locked (RTL) gas chromatography (GC)–mass spectrometry (MS) with simultaneous element-specific detection using a sulfur chemiluminescence detector (SCD) and a nitrogen chemiluminescence detector (NCD). Sequential heart-cuts of the 16 sulfur fractions were used to identify each individual sulfur compound in the unaged whisky. Twenty sulfur compounds were positively identified by a MS library search, linear retention indices (LRI), and formula identification using MS calibration software. Additionally eight formulas were also identified for unknown sulfur compounds. Simultaneous heart-cuts of the 16 sulfur fractions were used to produce the 2D RTL GC-SCD chromatograms for principal component analysis. PCA of the 2D RTL GC-SCD data clearly demonstrated the difference between unaged and aged whisky, as well as two different whisky samples. Fourteen sulfur compounds could be characterized as key sulfur compounds responsible for the changes in the aging step and/or the difference between two kinds of whisky samples. The determined values of the key sulfur compounds were in the range of 0.3–210ngmL−1 (RSD: 0.37–12%, n =3). [Copyright &y& Elsevier]

Abstract: Gas and liquid chromatography (GC and LC) coupled to mass spectrometry (MS) serve as the most powerful analytical tools commonly used to monitor pesticide residues in food, among other applications. However, both GC–MS and LC–MS are susceptible to matrix effects which can adversely affect quantification depending on the analyte, matrix, sample preparation, instrumentation, and operating conditions. Among the approaches that reduce matrix effects, the most common in pesticide residue applications is matrix-matched calibration because it is relatively inexpensive and simple. Also, it has been shown to work well during method validation when fortified samples are exactly matched with samples used for calibration. However, the quality of matrix-matched results in real-world analyses depends on the consistency of matrix effects among diverse samples. In this study, the variability of matrix effects was measured for 38 representative pesticides in 20 samples each (including different varieties) of rice, orange, apple, and spinach extracted using the “quick, easy, cheap, effective, rugged, and safe” (QuEChERS) method for analysis by LC–MS/MS and low-pressure GC–MS. Using LC–MS/MS, only oranges gave >20% matrix effects for a few pesticides. GC–MS exhibited larger matrix effects, but as in LC–MS/MS, the differences were reasonably consistent among the 20 samples tested. Main conclusions of this study are that for the conditions utilized: (1) matrix-matching was not needed for most pesticides in the simpler food matrices; and (2) for the more complex orange matrix, acceptably accurate quantitative results were achieved by using matrix-matching even with a different sample of the same type. However, full confidence cannot be extended to matrix-matched results, and for consequential applications such as regulatory enforcement, confirmatory analyses using alternate quantitative determinations should also be conducted. [Copyright &y& Elsevier]