Recent progress in food flavor analysis using gas chromatography-ion mobility spectrometry (GC-IMS).

Rapid, nondestructive, high-throughput testing and screening of volatile ingredients plays an important role in food flavor analysis. Gas chromatography-ion mobility spectrometry (GC-IMS) is a powerful technique for the separation and sensitive detection of volatile organic compounds. It has a fast response, high sensitivity, easy operation, and low cost. In this article, a brief introduction to the working principle of GC-IMS is presented. A summary of recent studies of different food flavor analysis applications is also provided, including food classification and adulteration, the evaluation of food freshness and spoilage, off-flavor detection, monitoring the processing of food products, and evaluation of aroma changes during food storage. Finally, future directions of GC-IMS are proposed.

Evaluation of the perceptual interaction among ester aroma compounds in cherry wines by GC-MS, GC-O, odor threshold and sensory analysis: An insight at the molecular level.

The ester aroma profiles of five Chinese cherry wines and the perceptual interaction among esters were investigated in this study. 24 esters were identified by Gas chromatography-olfactometry (GC-O) and Gas Chromatography-Mass Spectrometer (GC-MS). According to addition/omission analysis, seven volatile compounds among them were selected and studied using sensory profiling and multivariate statistic methods such as Principal Component Analysis (PCA). In sensory analysis, a significant reduction of olfactory threshold for total aromatic reconstitution was induced by the addition among each of them in Feller's additive model, which demonstrated their synergistic effects. The σ/τ plot showed that most of them were followed by a partial addition behavior. Furthermore, PCA indicated that the addition among each of them had a significant effect on fruity, floral, sweet and fermentation aroma intensity. Specifically, ethyl decanoate and methyl salicylate at sub-threshold concentrations were also likely to contribute to overall aroma. The results of perceptual interaction were mainly influenced by chemical structure and molecular polarity.

Inter-laboratory proficiency results of blood alcohol determinations at clinical and forensic laboratories in Italy.

BACKGROUND: Inter-laboratory proficiency schemes are widely used to control the performance of clinical and forensic toxicology laboratories. In 2016 the Laboratory of Environmental Hygiene and Forensic Toxicology - Venice (Italy) initiated an inter-laboratory proficiency test of blood-alcohol analysis. The number of participating laboratories gradually increased from 26 to 36. Furthermore, a few clinical laboratories were included if gas chromatographic (GC) methods were used for blood alcohol analysis. PROCEDURE: Whole blood was obtained from the Blood Transfusion Centre of the Venice Hospital and a mixture of sodium fluoride and potassium oxalate was added as a preservative and anticoagulant, respectively. Aliquots of the blood were spiked with certified pure ethanol to obtain target blood-alcohol concentrations (BACs) ranging from 0 to 5.0g/L. Two blood samples (4mL each) were included in each shipment to the participating laboratories. The laboratories were asked to provide information about number of replicate BAC determinations they made, the types of ethanol reference standards used, and inherent measurement uncertainty. The aim of the testing was to obtain a mean consensus value for the target BAC and to assess inter-laboratory imprecision. All procedures for registration and submission of results were done on-line. A confidential report and statistical evaluations were returned to the participants one week later. ANALYTICAL METHODS: All participants used head-space GC (HS-GC) for the analysis of ethanol in blood. More than 85% of participants used HS-GC with flame-ionization detection, whereas the others used mass spectrometry (MS) as a detector. More than 40% of the participating laboratories kept the blood samples frozen (-20°C) prior to analysis, whereas the others used refrigeration (+4°C). The preliminary validation tests showed that there were no statistically significant differences between BAC in frozen or refrigerated samples for a period of 20 days. RESULTS AND CONCLUSION: The statistical evaluation of results was done using an iterative procedure known as Algorithm A (ISO 13528:2015, C.3.1). This provides robust estimates for mean and standard deviation between laboratories and these were used as consensus values. More than 85% of participants provided satisfactory results (z-score <1) and 94% of laboratories were within z-score <2, based on five control samples. When a blood sample without any alcohol (blank) was sent for analysis, laboratories reported this as zero, 0.00g/L, below limit of detection (LOD) or not detected. Some type of consensus should be reached for reporting blank samples.

Two metrics for measuring orthogonality for two-dimensional chromatography.

Orthogonality can be used as a selection parameter for two-dimensional chromatography column selection (e.g. in GC × GC or LC × LC) or for method optimization purposes, both aiming for maximal orthogonality for a particular analytical application. In order to improve the concurrence of two-dimensional chromatography expert's orthogonality grading, two orthogonality metrics, %FIT and %BIN, were developed, evaluated and compared with the Asterisks orthogonality metric. The %BIN is a bin counting approach where the number of bins is fixed at 25 and deviations from the expected average number of peaks per bin is used as the basis for the orthogonality calculation. The %FIT is based on fitting polynomials of degree two, through the xy and the yx data and calculating the average minimal distance and standard deviation of all data points above and below the fitted polynomials. The orthogonality metrics were evaluated by using 14 different types of computer generated xy datasets and two measured LC × LC datasets. Both %FIT and %BIN, were shown to have a larger discriminative power than the Asterisks equations, and are in good agreement with the orthogonality scores for 2D-chromatograms provided by nine experts.

Identification of Key Odorants in Used Disposable Absorbent Incontinence Products.

PURPOSE: The purpose of this study was to identify key odorants in used disposable absorbent incontinence products. DESIGN: Descriptive in vitro study SUBJECTS AND SETTING:: Samples of used incontinence products were collected from 8 residents with urinary incontinence living in geriatric nursing homes in the Gothenburg area of Sweden. Products were chosen from a larger set of products that had previously been characterized by descriptive odor analysis. METHODS: Pieces of the used incontinence products were cut from the wet area, placed in glass bottles, and kept frozen until dynamic headspace sampling of volatile compounds was completed. Gas chromatography-olfactometry was used to identify which compounds contributed most to the odors in the samples. Compounds were identified by gas chromatography-mass spectrometry. RESULTS: Twenty-eight volatiles were found to be key odorants in the used incontinence products. Twenty-six were successfully identified. They belonged to the following classes of chemical compounds: aldehydes (6); amines (1); aromatics (3); isothiocyanates (1); heterocyclics (2); ketones (6); sulfur compounds (6); and terpenes (1). CONCLUSION: Nine of the 28 key odorants were considered to be of particular importance to the odor of the used incontinence products: 3-methylbutanal, trimethylamine, cresol, guaiacol, 4,5-dimethylthiazole-S-oxide, diacetyl, dimethyl trisulfide, 5-methylthio-4-penten-2-ol, and an unidentified compound.

Simple automatic strategy for background drift correction in chromatographic data analysis.

Chromatographic background drift correction, which influences peak detection and time shift alignment results, is a critical stage in chromatographic data analysis. In this study, an automatic background drift correction methodology was developed. Local minimum values in a chromatogram were initially detected and organized as a new baseline vector. Iterative optimization was then employed to recognize outliers, which belong to the chromatographic peaks, in this vector, and update the outliers in the baseline until convergence. The optimized baseline vector was finally expanded into the original chromatogram, and linear interpolation was employed to estimate background drift in the chromatogram. The principle underlying the proposed method was confirmed using a complex gas chromatographic dataset. Finally, the proposed approach was applied to eliminate background drift in liquid chromatography quadrupole time-of-flight samples used in the metabolic study of Escherichia coli samples. The proposed method was comparable with three classical techniques: morphological weighted penalized least squares, moving window minimum value strategy and background drift correction by orthogonal subspace projection. The proposed method allows almost automatic implementation of background drift correction, which is convenient for practical use.

Calculation and verification of blood ethanol measurement uncertainty for headspace gas chromatography.

An estimate was made of the measurement uncertainty for blood ethanol testing by headspace gas chromatography. While uncertainty often focuses on compliance to a single threshold level (0.08 g/100 mL), the existence of multiple thresholds, related to enhanced sentencing, subject age, or commercial vehicle licensure, necessitate the use of an estimate with validity across multiple specification levels. The uncertainty sources, in order of decreasing magnitude, were method reproducibility, linear calibration, recovery, calibrator preparation, reference material, and sample preparation. A large set of reproducibility data was evaluated (n = 15,433) in order to encompass measurement variability across multiple conditions, operators, instruments, concentrations and timeframes. The relative, combined standard uncertainty was calculated as ±2.7%, with an expanded uncertainty of ±8.2% (99.7% level of confidence, k = 3). Bias was separately evaluated through a recovery study using standard reference material from a national metrology institute. The uncertainty estimate was verified through the use of proficiency test (PT) results. Assigned values for PT results and their associated uncertainties were calculated as robust means (x*) and standard deviations (s*) of participant values. Performance scores demonstrated that the uncertainty estimate was appropriate across the full range of PT concentrations (0.010-0.370 g/100 mL). The use of PT data as an empirical estimate of uncertainty was not examined. Until providers of blood ethanol PT samples include details on how an assigned value is obtained along with its uncertainty and traceability, the use of PT data should be restricted to the role of verification of uncertainty estimates.

A GC-ECD method for estimation of free and bound amino acids, gamma-aminobutyric acid, salicylic acid, and acetyl salicylic acid from Solanum lycopersicum (L.).

A gas chromatograph with electron capture detection method for estimation of selected metabolites--amino acids (free and bound), gamma-aminobutyric acid (GABA), salicylic acid (SA), and acetyl salicylic acid (ASA) from tomato--is reported. The method is based on nitrophenylation of the metabolites by 1-fluoro-2, 4-dinitrobenzene under aqueous alkaline conditions to form dinitophenyl derivatives. The derivatives were stable under the operating conditions of GC. Analysis of bound amino acids comprised perchloric acid precipitation of protein, alkylation (carboxymethylation) with iodoacetic acid, vapor-phase hydrolysis, and derivatization with 1-fluoro-2,4-dinitrobenzene in that order. The metabolites were resolved in 35 min, using a temperature-programmed run. The method is rapid, sensitive, and precise. It easily measured the typical amino acids (aspartate, asparagine, glutamate, glutamine, alanine, leucine, lysine, and phenylalanine) used for identification and quantification of a protein, resolved amino acids of the same mass (leucine and isoleucine), satisfactorily measured sulfur amino acid (methionine, cystine, and cysteine), and quantified GABA, SA, and ASA, as well. The developed method was validated for specificity, linearity, and precision. It has been applied and recommended for estimation of 25 metabolites from Solanum lycopersicum (L.).

Clinical reliability of non-organoleptic oral malodour measurements.

AIM: Measurement of volatile sulphur compounds (VSC) by portable sulphur monitors (Halimeter, OralChroma) is a common practice for diagnosis of oral malodour. In this study, the clinical value of these devices was examined. MATERIALS AND METHODS: Two hundred and eighty patients with bad breath complaints attending a halitosis consultation were enrolled. Organoleptic scores were given by a trained and calibrated judge, before measurement of the VSC levels (Halimeter, OralChroma), to avoid any bias. RESULTS: Significant correlations were found between the organoleptic assessment, the Halimeter, and the OralChroma (R=0.74 for organoleptic versus Halimeter; 0.66 for organoleptic versus OralChroma; 0.63 for Halimeterversus OralChroma). The sensitivity and specificity (with regard to the organoleptic score) to detect patients with/without oral malodour for the Halimeter were 63% and 98%, respectively, and for the OralChroma 69% and 100% when using the cutoffs suggested by the manufacturer. By lowering these values, sensitivity could be improved without a significant decrease in specificity (both devices). CONCLUSIONS: We concluded that the measurement of the VSC levels can be used as an adjunct to the organoleptic assessment. Thresholds should be revisited in order to improve their clinical utility. These devices can prove the absence of malodour in case of pseudo-halitosis.

Comparative multiple quantitative structure-retention relationships modeling of gas chromatographic retention time of essential oils using multiple linear regression, principal component regression, and partial least squares techniques.

Quantitative structure-retention relationships (QSRR) models were built for a data set consisting of 96 essential oils and used to predict their gas chromatographic (GC) retention times (t(R)). Multiple linear regression (MLR), principal component regression (PCR), and partial least squares (PLS) have been applied to build different QSRR models by using 13 nonzero E-state indexes and 56 descriptors calculated from TSAR software. The three chemometric methods (MLR, PCR, and PLS) for evaluation of GC t(R) values of essential oils have been compared. The best model based on the whole data set derived from MLR model (model M2) appears to be the best predictive power (r(2)=0.9689 and q(2)=0.9631) for this data set. The whole data set was splitted into a training set consisting of 72 compounds and a test set consisting of 24 compounds. The model based on the training set derived from MLR offered the highest r(2) of 0.9756 and q(2) of 0.9693. The best model base on the training set obtained from PLS not only showed a good internal predictive power (r(2)=0.9703 and q(2)=0.9633) but also offered the highest external predictive power (R(2)=0.9588 and q(2)(ext)=0.9572). The results showed that two E-state indexes (sssCH and sOH) and five molecular connective indices ((1)chi(B), (2)chi(p), (3)chi(C), (4)chi(C), and (6)chi(p)) closely relate to the GC t(R) values of essential oils. The applicability domain of the QSRR models were defined by control leverage values (h*) and the models can be used to predict the unknown compounds falling in this domain.

Investigation of different linear and nonlinear chemometric methods for modeling of retention index of essential oil components: concerns to support vector machine.

The quantitative structure-retention relationship (QSRR) of the essential oil components against the gas chromatography retention index (RI) was studied. The genetic algorithm (GA) was employed to select the variables that resulted in the best-fitted models. After the variables were selected, the linear multivariate regressions [e.g. the multiple linear regression (MLR), the partial least squares (PLS)] as well as the nonlinear regressions [e.g. the polynomial PLS (poly-PLS), the support vector machine (SVM)] were utilized to construct the linear and nonlinear QSRR models. The obtained results using SVM were compared with those of MLR, PLS and poly-PLS, exhibiting that the SVM model demonstrated a better performance than that of the other models. The relative standard error SE (%) of the training set and the test set for the SVM model was 1.96 and 4.25, and the square correlation coefficients were 0.987 and 0.962 respectively, while the square correlation coefficient of the cross validation (Q(2)) on the SVM model was 0.963, revealing the reliability of this model. The resulting data indicated that SVM could be used as a powerful modeling tool for the QSRR studies. This is the first research on the QSRR of the essential oil compounds against the retention index using the SVM.

Combination of dynamic time warping and multivariate analysis for the comparison of comprehensive two-dimensional gas chromatograms: application to plant extracts.

Comprehensive two-dimensional gas chromatography (GC x GC) is now recognized as the preferred technique for the detailed analysis and characterization of complex mixtures of volatile compounds. However, for comparison purposes, taking into account all the information contained in the chromatogram is far from trivial. In this paper, it is shown that the combination of peak alignment by dynamic time warping and multivariate analysis facilitated the comparison of complex chromatograms of tobacco extracts. The comparison is shown to be efficient enough to provide a clear discrimination among three types of tobacco. A tentative interpretation of loadings is presented in order to give access to the compounds which differ from one sample to another. Once located, mass spectrometry was used to identify markers of tobacco type.

Data analysis programs for comprehensive two-dimensional chromatography.

User-friendly and easy-to-use laboratory-written programs for visualisation and interpretation of comprehensive two-dimensional chromatographic data were developed. The programs that are not tied to any particular commercial instrument, and data obtained either by comprehensive two-dimensional liquid (LC x LC) or gas (GC x GC) chromatography can be analysed. Operations of the programs allow visualisation of 2D and 3D plots, comparison of two 2D plots at a time, as well as determination of retention times and peak heights and volumes.

Propriedades antioxidantes em subproduto do pedúnculo de caju (Anacardium occidentale L. ): efeito sobre a lipoperoxidação e o perfil de ácidos graxos poliinsaturados em ratos / Antioxidant properties in cashew apple byproduct (Anacardium occidentale L. ): effect on lipoperoxidation and on the polyunsaturated fatty acids profile in rats

O caju (Anacardium occidentale L.) apresenta substâncias fenólicas, as quais são atribuídas propriedades antioxidantes. Sendo assim, o presente trabalho objetivou verificar a capacidade antioxidante em subproduto, ou seja, no bagaço do pedúnculo do caju. O potencial antioxidante do extrato hidroalcoólico (EHAlc) do bagaço do pedúnculo de caju foi avaliado em sistema de varredura do radical 2,2'-difenil-1-picrilhidrazilo (DPPHò) e em ensaio in vivo. No sistema DPPH, o extrato demonstrou atividade antioxidante de cerca de 95% em sua maior concentração (1000 µg/mL). Para o estudo in vivo, foram utilizados ratos Wistar administrando oralmente EHAlc (200 e 400 mg/kg de peso corpóreo) por 30 dias e analisados os tecidos plasmático, hepático e cerebral. Não houve alterações na peroxidação lipídica no plasma e no fígado dos animais tratados comparados ao grupo controle. Contudo, foi observada redução da lipoperoxidação no cérebro dos grupos tratados. Além do mais, neste tecido, os animais tratados apresentaram maior quantidade de ácidos graxos poliinsaturados (AGPI), destacando-se o ácido docosahexaenóico (DHA). Estes resultados indicam que o EHAlc contém antioxidantes naturais efetivos e que podem contribuir na redução da lipoperoxidação e preservação dos AGPICL no tecido cerebral de ratos, dando indícios da capacidade antioxidante do bagaço do pedúnculo de caju CCP-76.

The cashew apple (Anacardium occidentale L.) contains phenolic compounds usually related with antioxidant properties. Then, the aim of this study was to investigate its antioxidant capacity. The antioxidant capacity of the hydroalcoholic extract of the cashew apple pulp (EHAlc.) was assessed for the scavenging of the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) by in vitro method and by an in vivo essay. For this essay a 30-day oral (gavage, EHAlc. 200 and 400 mg/kg) study was conducted in Wistar male rats, evaluating hepatic, plasma and brain tissues. In DPPH model, the extract demonstrated antioxidant activity of 95% (largest concentration, 1000 µg/ mL). There were found no relevant peroxidation comparing the treated animals with the control group. However, the treated group presented a lower level of brain lipoperoxidation. Also in the treated animals brain tissue was found the largest amount of polyunsaturated fatty acids (PUFA), mainly docosahexaenoic (DHA). Therefore, the analyzed extract from cashew apple pulp clone CCP-76 contains effective natural antioxidants, responsible for free radical scavenging in vitro and also for decreasing the brain lipoperoxidation and keeping the PUFAS levels in Wistar rats.

QSPR study on GC relative retention time of organic pesticides on different chromatographic columns.

In the present study, Lu index and distance-based atom type topological index (DAI) previously developed in our team, were introduced and combined with molecular electronegativity chi ep to characterize quantitative structure-property relationship of GC relative retention time (RRT) for several types of structurally diverse organic pesticides on the four kinds of chromatographic columns. Using multiple linear regression technique, four several-variable models are obtained with the estimations correlation coefficient (R(2)) being between 0.9655 and 0.9285, and the correlation coefficient (R(2)cv) in the leave-one-out cross-validation procedure are between 0.9560 and 0.9143, respectively. The results in this study indicate that the three topological indices Lu index, DAI, and molecular electronegativity chi ep can predict the gas chromatographic RRT of organic pesticides with diverse hetero-atoms.

An accurate and nondestructive GC method for determination of cocaine on US paper currency.

The presence of cocaine on US paper currency has been known for a long time. Banknotes become contaminated during the exchange, storage, and abuse of cocaine. The analysis of cocaine on various denominations of US banknotes in the general circulation can provide law enforcement circles and forensic epidemiologists objective and timely information on epidemiology of illicit drug use and on how to differentiate money contaminated in the general circulation from banknotes used in drug transaction. A simple, nondestructive, and accurate capillary gas chromatographic method has been developed for the determination of cocaine on various denominations of US banknotes in this study. The method comprises a fast ultrasonic extraction using water as a solvent followed by a SPE cleanup process with a C(18) cartridge and capillary GC separation, identification, and quantification. This nondestructive analytical method has been successfully applied to determine the cocaine contamination in US paper currency of all denominations. Standard calibration curve was linear over the concentration range from the LOQ (2.00 ng/mL) to 100 microg/mL and the RSD less than 2.0%. Cocaine was detected in 67% of the circulated banknotes collected in Southeastern Massachusetts in amounts ranging from approximately 2 ng to 49.4 microg per note. On average, $5, 10, 20, and 50 denominations contain higher amounts of cocaine than $1 and 100 denominations of US banknotes.

Determination of organotins in aquatic food by gas chromatography with pulsed flame photometric detection.

A method based on gas chromatography (GC)-pulsed flame photometric detection (PFPD) was developed to determine the levels of organotins in aquatic food. After being purified by gel-permeation chromatography in ethyl actate-tetrahydrofuran, the organotin compounds were derivatized by pentylmagnesium bromide. The derivative products were injected into the GC system and detected by PFPD (sulfur mode). The method was validated by analysis of the certified reference material and spiked samples. Recoveries of organotins ranged from 84.1 to 116.6% with relative standard deviation between 1.3 and 16.0% when spiked at levels of 2, 10, and 40 microg/kg. The limits of detection varied from 0.1 to 1.2 microg/kg for shellfish and 0.1 to 0.5 microg/kg for fish. The proposed method was suitable for determining organotins in aquatic foods.

Analysis of trace amounts of carbon dioxide, oxygen and carbon monoxide in nitrogen using dual capillary columns and a pulsed discharge helium ionisation detector.

Gas mixtures of trace amounts of carbon dioxide (CO(2)), dioxygen (O(2)), and carbon monoxide (CO) in dinitrogen (N(2)) were separated and quantified using parallel dual capillary columns and pulsed discharge helium ionisation detection (PDHID). The detection limits (9 x 10(-9) mol mol(-1) for CO(2), 7 x 10(-9) mol mol(-1) for O(2) and 37 x 10(-9) mol mol(-1) for CO) were lower than those reported previously for similar methods. Uncertainties were calculated and results were validated by comparison of the CO and CO(2) results with those obtained using conventional methods. The method was also used to analyse nitrogen, carbon dioxide and carbon monoxide in oxygen.

Detection of carbon monoxide production as a result of the interaction of five volatile anesthetics and desiccated sodalime with an electrochemical carbon monoxide sensor in an anesthetic circuit compared to gas chromatography.

OBJECTIVES: There is a continuing risk of production of toxic levels of carbon monoxide (CO) as a result of interaction of volatile anesthetics and desiccated strong base carbon dioxide absorbents like soda lime. The aim of this study is to establish the reliability of detection of CO levels by an electrochemical carbon monoxide sensor compared to gas chromatography. METHODS: Completely desiccated sodalime was conducted through a circle anesthesia system connected to an artificial lung. For different rates of CO production, a low flow anesthesia with a oxygen/nitrous oxide mixture was maintained using five volatile anesthetics. For quantification of CO production, a portable gas chromatograph (GC) was connected to this setup, as well as a Bedfont EC40 electrochemical carbon monoxide sensor (ES) with a claimed reliable sensitivity of 0-200 parts per million (ppm) and a maximum detection range of more than 5500 ppm. To assess the agreement between the GC and ES measurements the intra class correlation coefficient (ICC) and the 95% limits of agreement were calculated. Bland and Altman scatterplots were made to visualize the difference between measurements. RESULTS: For concentrations up to 200 ppm, no significant differences between the GC and ES mean CO measurements were found in the halothane experiments. However CO was not accurately measured at every moment during these experiments by the ES. For concentrations above 200 ppm the results of the two instruments differed significantly. The ES malfunctioned when exposed to sevoflurane and desiccated sodalime. CONCLUSIONS: From these data we conclude that the ES can only be used as an indicator of CO production. When this sensor is used with sevoflurane and desiccated sodalime it is not capable of normal operation. The use of a strong base free carbon dioxide absorbent is therefore recommended.

Evaluation of enantioselective gas chromatography for the determination of minute deviations from racemic composition of alpha-amino acids with emphasis on tyrosine: accuracy and precision of the method.

Whereas the determination of high enantiomeric fractions (EF) of chiral compounds is very well established, the accurate determination of small deviations from racemic compositions has not yet received much attention despite its relevance to studies dealing with the origin of homochirality, where only small initial enantiomeric bias is expected. Racemic samples of representative alpha-amino acids were derivatized as N-(O,S)-trifluoroacetyl/ethylesters and analyzed by enantioselective gas chromatography (GC) on fused silica capillaries coated with the chiral stationary phases (CSPs) Chirasil-D-Val, Chirasil-L-Val, and Lipodex E with GC/FID and GC/MS detection. The validation (accuracy and precision) of the determination of the enantiomeric fraction EF of the D-enantiomer in racemic or near-racemic compositions for 10 DL-alpha-amino acids obtained from commercial sources has been carried out. Emphasis is given to DL-tyrosine, the enantiomers of which have recently been claimed to show different crystallization properties. Values of EF obtained from GC measurements using CSPs were compared with those from CE using chiral mobile phase additives. While the precision of the GC method is generally better than 0.08% for all DL-alpha-amino acids studied, accuracy (trueness) of determination of amino acids with polar side chains is poorer than expected from the precision as a result of systematic errors. The accuracy determined relied on measurements on two oppositely configurated CSPs.