Benchmarking breath analysis using peppermint approach with gas chromatography ion mobility spectrometer coupled to micro thermal desorber.

The Peppermint Initiative, established within the International Association of Breath Research, introduced the peppermint protocol, a breath analysis benchmarking effort designed to address the lack of inter-comparability of outcomes across different breath sampling techniques and analytical platforms. Benchmarking with gas chromatography-ion mobility spectrometry (GC-IMS) using peppermint has been previously reported however, coupling micro-thermal desorption (µTD) to GC-IMS has not yet, been benchmarked for breath analysis. To benchmarkµTD-GC-IMS for breath analysis using the peppermint protocol. Ten healthy participants (4 males and 6 females, aged 20-73 years), were enrolled to give six breath samples into Nalophan bags via a modified peppermint protocol. Breath sampling after peppermint ingestion occurred over 6 h att= 60, 120, 200, 280, and 360 min. The breath samples (120 cm3) were pre-concentrated in theµTD before being transferred into the GC-IMS for detection. Data was processed using VOCal, including background subtractions, peak volume measurements, and room air assessment. During peppermint washout, eucalyptol showed the highest change in concentration levels, followed byα-pinene andß-pinene. The reproducibility of the technique for breath analysis was demonstrated by constructing logarithmic washout curves, with the average linearity coefficient ofR2= 0.99. The time to baseline (benchmark) value for the eucalyptol washout was 1111 min (95% CI: 529-1693 min), obtained by extrapolating the average logarithmic washout curve. The study demonstrated thatµTD-GC-IMS is reproducible and suitable technique for breath analysis, with benchmark values for eucalyptol comparable to the gold standard GC-MS.

Deep Learning Based Prediction of Gas Chromatographic Retention Indices for a Wide Variety of Polar and Mid-Polar Liquid Stationary Phases.

Prediction of gas chromatographic retention indices based on compound structure is an important task for analytical chemistry. The predicted retention indices can be used as a reference in a mass spectrometry library search despite the fact that their accuracy is worse in comparison with the experimental reference ones. In the last few years, deep learning was applied for this task. The use of deep learning drastically improved the accuracy of retention index prediction for non-polar stationary phases. In this work, we demonstrate for the first time the use of deep learning for retention index prediction on polar (e.g., polyethylene glycol, DB-WAX) and mid-polar (e.g., DB-624, DB-210, DB-1701, OV-17) stationary phases. The achieved accuracy lies in the range of 16-50 in terms of the mean absolute error for several stationary phases and test data sets. We also demonstrate that our approach can be directly applied to the prediction of the second dimension retention times (GC × GC) if a large enough data set is available. The achieved accuracy is considerably better compared with the previous results obtained using linear quantitative structure-retention relationships and ACD ChromGenius software. The source code and pre-trained models are available online.

Current analytical methods for determination of glucosinolates in vegetables and human tissues.

Numerous epidemiological studies have indicated the potential effects of glucosinolates and their metabolites against cancer as well as other non-communicable diseases, such as cardiovascular disease and neurodegenerative disorders. However, information on the presence and quantity of glucosinolates in commonly consumed vegetables and in human fluids is sparse, largely because well-standardised methods for glucosinolate determination are not available, resulting in published data being inconsistent and conflicting. Thus, studies published since 2002 on the most recent developments of glucosinolate extraction and identification have been collected and reviewed with emphasis on determination of the intact glucosinolates by LC-MS and LC-MS/MS. This overview highlights the glucosinolate extraction methods used, the stability of glucosinolates during extraction, the availability of stable isotope labelled internal standards and the use of NMR for purity analysis, as well as the current analytical techniques that have been applied for glucosinolate analysis, e.g. liquid chromatography with mass spectrometric detection (LC-MS). It aims to interpret the findings with a focus on the development of a validated method, which will help to determine the glucosinolate content of vegetative plants and human tissues, and the identification and determination of selected glucosinolate metabolites.

Standardization of chromatographic signals - Part I: Towards obtaining instrument-agnostic fingerprints in gas chromatography.

One of the main causes for the sparse use of multivariate analytical methods in routine laboratory work is the dependency on the measuring instrument from which the analytical signal is acquired. This issue is especially critical in chromatographic equipment and results in limitations of their applicability. The solution to this problem is to obtain a standardized instrument-independent signal -or instrument-agnostic signal- regardless of the measuring instrument or of the state of the same instrument from which it has been acquired. The combined use of both internal and external standard series, allows us to have external and transferable references for the normalization of both the intensity and the position of each element of the data vector being arranged from the raw signal. From this information, a simple mathematical data treatment process is applied and instrument-agnostic signals can be secured. This paper describes and applies the proposed methodology to be followed for obtaining standardized instrumental fingerprints from two significant fractions of virgin olive oil (volatile organic compounds and triacylglycerols), obtained by gas chromatography coupled to mass spectrometry (GC-MS) and analysed with two temperature conditions (conventional and high-temperature, respectively). The results of both case studies show how the instrument-agnostic fingerprints obtained are coincidental, regardless of the state of the chromatographic system or the time of acquisition.

A unique data analysis framework and open source benchmark data set for the analysis of comprehensive two-dimensional gas chromatography software.

Comprehensive two-dimensional gas chromatography (GC × GC) is amongst the most powerful separation technologies currently existing. Since its advent in early 1990, it has become an established method which is readily available. However, one of its most challenging aspects, especially in hyphenation with mass spectrometry is the high amount of chemical information it provides for each measurement. The GC × GC community agrees that there, the highest demand for action is found. In response, the number of software packages allowing for in-depth data processing of GC × GC data has risen over the last couple of years. These packages provide sophisticated tools and algorithms allowing for more streamlined data evaluation. However, these tools/algorithms and their respective specific functionalities differ drastically within the available software packages and might result in various levels of findings if not appropriately implemented by the end users. This study focuses on two main objectives. First, to propose a data analysis framework and second to propose an open-source dataset for benchmarking software options and their specificities. Thus, allowing for an unanimous and comprehensive evaluation of GC × GC software. Thereby, the benchmark data includes a set of standard compound measurements and a set of chocolate aroma profiles. On this foundation, eight readily available GC × GC software packages were anonymously investigated for fundamental and advanced functionalities such as retention and detection device derived parameters, revealing differences in the determination of e.g. retention times and mass spectra.

A step forward in the equivalence between thermal and differential-flow modulated comprehensive two-dimensional gas chromatography methods.

Comprehensive two-dimensional gas chromatography (GC×GC) based on flow-modulation (FM) is gaining increasing attention as an alternative to thermal modulation (TM), the recognized GC×GC benchmark, thanks to its lower operational cost and rugged performance. An accessible, rational procedure to perform method translation between the two platforms would be highly valuable to facilitate compatibility and consequently extend the flexibility and applicability of GC×GC. To enable an effective transfer, the methodology needs to ensure preservation of the elution pattern, separation power, and sensitivity. Here, a loop-type thermal modulation system with dual detection (TM-GC×GC-MS/FID) used for the targeted analysis of allergens in fragrances is selected as reference method. Initially, six different columns configurations are systematically evaluated for the flow-modulated counterpart. The set-up providing the most consistent chromatographic separation (20 m x 0.18 mm dc x 0.18 µm df + 1.8 m x 0.18 mm dc x 0.18 µm df) is further evaluated to assess its overall performance in terms of sensitivity, linearity, accuracy, and pattern reliability. The experimental results convincingly show that the method translation procedure is effective and allows successful transfer of the target template metadata. Additionally, the FM-GC×GC-MS/FID system is suitable for challenging applications such as the quantitative profiling of complex fragrance materials.

Selection of calibration compounds for selectivity evaluation of wall-coated, open-tubular columns for gas chromatography by the solvation parameter model.

To facilitate faster selectivity evaluation of wall-coated, open-tubular columns using the solvation parameter model a reduced set of calibration compounds is identified and validated for the temperature ranges 60-140 °C and 160-260 °C. The Kennard-Stone uniform mapping algorithm is used to identify the calibration compounds from a larger database of compounds with known retention properties previously adopted for column selectivity evaluation. Thirty-five compounds for each temperature range are required to minimize the standard deviation of the system constants used for selectivity evaluation and to minimize differences between system constants determined by conventional calibration and the reduced calibration compounds. The models for the reduced calibration compounds on ten siloxane-based and poly(ethylene glycol) stationary phases have a coefficient of determination of 0.984 to 0.998 and standard error of the estimate of 0.012 to 0.30. The predictive capability of models is evaluated for the reduced sets of calibration compounds using external test sets with ranking of the calibration models by changes in the average error, average absolute error and root mean square error of prediction for the test sets. For the selected thirty-five reduced calibration compounds the range for the average absolute error was 0.014 to 0.033 and 0.016 to 0.040 for the root mean square error of prediction for the independent test sets.

A Single-Column Gas Chromatography Method for Quantifying Toxic Alcohols.

BACKGROUND: Rapid identification and quantification of toxic alcohols and ethylene glycol is imperative for appropriate treatment. Clinical laboratories frequently rely on direct injection gas chromatography (GC) methods, but these methods require inlet maintenance and multiple GC systems. To overcome these challenges, we developed a single-column headspace GC method for both toxic alcohols and glycols that streamlines patient sample analysis for toxic alcohol ingestion. METHODS: Optimal parameters for nonderivatized (volatile) and derivatized (glycol) plasma samples were determined using a 7890 A headspace sampler, an Agilent 7697 A GC system, a DB-200 column, and a flame ionization detector. Limit of Quantification (LoQ), linearity, imprecision, carry-over, method comparison, and interference studies were performed using quality control materials and prepared plasma samples. RESULTS: Our volatile method is linear to 3000 mg/L (ethanol) with LoQ concentrations below 20 mg/L (ethanol). The glycol method is linear to 2000 mg/L (ethylene glycol) with LoQ concentrations below 40 mg/L (ethylene glycol). Total assay impression ranged from 1.7% for ethanol to 13.3% for propylene glycol. Both methods were free of sample carryover and compared favorably with a similar clinical method at an outside laboratory. Propionic acid, an accumulating metabolite in methylmalonic acidemia that interferes with ethylene glycol identification by a different method, did not interfere with the ethylene glycol method reported here. CONCLUSIONS: Our single-column headspace GC method provides reliable, robust, and rapid identification and quantification of commonly encountered toxic alcohols. Clinical laboratories relying on direct injection Gas Chromatography (GC) for toxic alcohol analysis face challenges including frequent inlet maintenance, sample carryover, or the need for separate GC systems for volatile and glycol analysis. We summarize our development and optimization of two headspace GC methods for nonderivatized (volatile) and derivatized (glycol) plasma samples that use a single DB-200 analytical column. These methods are comparable to other GC methods, not prone to sample carryover, eliminate the need for multiple GC systems or columns, and are readily applicable to other laboratories that provide toxic alcohol analysis.

Homogeneity assessment of reference materials for sensory analysis of liquid foodstuffs. The virgin olive oil as case study.

Sensory properties are critical characteristics that determine quality and can be evaluated by trained tasting panels. The panels function as multi-sensor measuring instrument and need the use of reference materials (RMs) for training. The homogeneity between units packaged from a batch of RM can be evaluated by gas chromatography coupled to flame ionization detection (GC-FID), using this instrumental technique as an alternative to sensory analysis. For this purpose, the fingerprint methodology is applied, taking into account that the homogeneity assessment will be based on evaluating the similarity between the fingerprints of the fraction of volatile organic compounds acquired from samples representative of the batch. The proposed methodology is applied with good results to evaluate the homogeneity of several RMs for sensory analysis of virgin olive oil samples, using similarity indices, control charts and exploratory analysis of multivariate data to observe the grouping RM and fingerprint regions representative of each defect.

Problem in the molecular area of polar probe molecules used in inverse gas chromatography.

Although the inverse gas chromatography technique has been used to measure the surface acid-base properties for almost 50 years, several basic problems still hinder its further development and application. One of the problems is that for the polar probe molecules of dichloromethane, acetone, ethyl acetate, tetrahydrofuran, and ethanol, the molecular area of each probe has different values in literature. In this paper, we point out the incorrect molecular area values presented in the literature by comparing these values with those indicated in Smallwood's Handbook of Organic Solvent Properties. The correct molecular area values of 11 polar probes are determined by plotting the molecular areas of the polar probes versus the van der Waals surface areas reported in the handbook. The correct molecular areas for six common polar probes, namely, dichloromethane, trichloromethane, acetone, ethyl acetate, diethyl ether, and tetrahydrofuran, are 38.0, 44.0, 42.5, 48.0, 47.0, and 45.0 Å2, respectively. Benzene is a specific molecule with a conjugated π-bond structure, and its molecular area is estimated to be larger than that of other molecules. Therefore, benzene is unsuitable for use as a probe molecule.

Gas chromatography system constant database over an extended temperature range for nine open-tubular columns.

The solvation parameter model is used to characterize the retention properties of poly(octylmethylsiloxane), poly(dimethyldiphenylsiloxane), silphenylene-dimethylsiloxane copolymer, poly(dimethylmethyltrifluoropropylsiloxane), poly(3-cyanopropylphenyldimethylsiloxane), and poly(ethylene glycol) (SPB-Octyl, HP-5, Rxi-17, Rxi-5Sil MS, Rtx-OPP, DB-1701, DB-225, Rtx-440 and HP-INNOWAX) stationary phases over an extended temperature range from 60 °C to close to the maximum column operating temperature. System maps constructed from the system constant database are used to evaluate the influence of temperature on the contribution of intermolecular interactions to differences in selectivity. None of the stationary phases are hydrogen-bond acids. Increasing temperature reduces the contribution from cavity formation/dispersion, dipole-type interactions and hydrogen-bond basicity in a stationary phase specific manner with their preservation to the highest temperature studied for each column. Electron lone pair interactions are generally repulsive at lower temperatures becoming attractive and leading to an increase in retention at higher temperatures.

Development and Validation of an Analytical Method to Quantitate Tris(chloroisopropyl)phosphate in Rat and Mouse Plasma using Gas Chromatography with Flame Photometric Detection.

Tris(chloropropyl)phosphate (TCPP) is an organophosphorus flame retardant (OPFR) and plasticizer increasingly used in consumer products and as a replacement for brominated flame retardants. Commercially available TCPP is a mixture of four structural isomers the most abundant of which is tris(1-chloro-2-propyl)phosphate (TCPP-1). Although there is a widespread use of TCPP and potential for human exposure, there is limited data on the safety or toxicity of TCPP. The National Toxicology Program is conducting long-term studies to examine the toxicity of the TCPP in rats after lifetime exposure, including perinatal oral exposure. Quantitative estimates of internal dose are essential to interpret toxicological findings in rodents. To aid in this, a method was fully validated to quantitate the most abundant isomer, TCPP-1, in female Harlan Sprague Dawley (HSD) rat and B6C3F1 mouse plasma with partial validation in male rat plasma, and male and female mouse plasma. The method used protein precipitation using trichloroacetic acid followed by the extraction with toluene, and analysis by gas chromatography with flame photometric detection. The performance of the method was evaluated over 5-70 ng TCPP-1/mL plasma. The method was linear (r ≥ 0.99), accurate (inter-day relative error: ≤ ± -7.2) and precise (inter-batch relative standard deviation: ≤27.5%). The validated method has lower limits of quantitation and detection of ~5 and 0.9 ng/mL, respectively, in female HSD rat plasma and can be used on samples as small as 50 µL demonstrating the applicability to plasma samples from toxicology studies.

Polar and non-polar intracellular compounds from microalgae: Methods of simultaneous extraction, gas chromatography determination and comparative analysis.

A method to simultaneously extract polar (PC) and non-polar compounds (NPC) from microalgae was developed for further determination of intracellular metabolites by gas chromatography. The proposed method was validated and used to characterize two Chlorophyceae, Chlorella vulgaris and Scenedesmus obliquus, and two Cyanobacteria, Aphanothece microscopica Nagëli and Phormidium autumnale. The compounds were extracted with a reduced amount of organic solvent mixture (methanol-chloroform), compared to the reference method, under different conditions of homogenization and/or cell disruption. The NPC were derivatized by acid catalysis, whereas the PC fraction was derivatized using N-methyl,N-tert-Butyldimethylsilyltrifluoroacetamide (MTBSTFA) in alkaline medium. The following parameters for method validation were considered: selectivity, linearity, limit of detection (LOD), limit of quantitation (LOQ), precision, and accuracy. All methods of homogenization and cell disruption extracted both PC and NPC from Chlorophyceae and Cyanobacteria. Derivatization of PC presented satisfactory validation parameters. Eleven fatty acids, six free amino acids, and three organic acids were found within the evaluated microalgae species, succinic, malic, and citric acids, important intermediates of the tricarboxylic acid cycle. Glutamic acid was the amino acid found in greatest quantities in all species. Chlorophyceae presented a higher concentration of unsaturated fatty acids, while Cyanobacteria had more saturated fatty acids. Thus, the proposed method was suitable to metabolically characterize both PC and NPC from microalgae.

Synthesis of Alkyl-Glycerolipids Standards for Gas Chromatography Analysis: Application for Chimera and Shark Liver Oils.

Natural O-alkyl-glycerolipids, also known as alkyl-ether-lipids (AEL), feature a long fatty alkyl chain linked to the glycerol unit by an ether bond. AEL are ubiquitously found in different tissues but, are abundant in shark liver oil, breast milk, red blood cells, blood plasma, and bone marrow. Only a few AEL are commercially available, while many others with saturated or mono-unsaturated alkyl chains of variable length are not available. These compounds are, however, necessary as standards for analytical methods. Here, we investigated different reported procedures and we adapted some of them to prepare a series of 1-O-alkyl-glycerols featuring mainly saturated alkyl chains of various lengths (14:0, 16:0, 17:0, 19:0, 20:0, 22:0) and two monounsaturated chains (16:1, 18:1). All of these standards were fully characterized by NMR and GC-MS. Finally, we used these standards to identify the AEL subtypes in shark and chimera liver oils. The distribution of the identified AEL were: 14:0 (20-24%), 16:0 (42-54%) and 18:1 (6-16%) and, to a lesser extent, (0.2-2%) for each of the following: 16:1, 17:0, 18:0, and 20:0. These standards open the possibilities to identify AEL subtypes in tumours and compare their composition to those of non-tumour tissues.

Efficient quantification of water content in edible oils by headspace gas chromatography with vapour phase calibration.

BACKGROUND: An automated and accurate headspace gas chromatographic (HS-GC) technique was investigated for rapidly quantifying water content in edible oils. In this method, multiple headspace extraction (MHE) procedures were used to analyse the integrated water content from the edible oil sample. A simple vapour phase calibration technique with an external vapour standard was used to calibrate both the water content in the gas phase and the total weight of water in edible oil sample. After that the water in edible oils can be quantified. RESULTS: The data showed that the relative standard deviation of the present HS-GC method in the precision test was less than 1.13%, the relative differences between the new method and a reference method (i.e. the oven-drying method) were no more than 1.62%. CONCLUSION: The present HS-GC method is automated, accurate, efficient, and can be a reliable tool for quantifying water content in edible oil related products and research. © 2017 Society of Chemical Industry.

Numerical study and theoretical performance limit of interconnected multi-capillary gas chromatography columns with perfectly ordered pillar patterns.

We present the results of a theoretical and numerical study of the chromatographic performance of a novel type of microfabricated GC column. The column consists of an array of rectangular flow diverters (pillars), creating a network of perfectly ordered, interconnected and tortuous flow-through paths. Using van Deemter and kinetic plots of simulated band broadening data, we could demonstrate that the proposed column structure performs as a bundle of parallel open-tubular capillaries with rectangular cross-section, connected by a regular pattern of channel-intermixing points that allow compensating for inevitable channel-to-channel differences in migration velocity without adding any significant dispersion themselves. The established kinetic plots also allowed to propose design rules for the optimal distance between the pillars as a function of the desired separation efficiency and the available column pressure. The simulations also allowed establishing an expression for the plate height as a function of the velocity of the carrier gas. Results are also compared to the results of a recent experimental study.

A system map for the ionic liquid stationary phase 1,12-di(tripropylphosphonium)dodecane bis(trifluoromethylsulfonyl)imide for gas chromatography.

The solvation parameter model is used to prepare a system map for the retention of volatile organic compounds on the ionic liquid stationary phase 1,12-di(tripropylphosphonium)dodecane bis(trifluoromethylsulfonyl)imide (SLB-IL60) by gas chromatography over the temperature range 80-280°C. Retention is governed by dispersion, dipole-type and hydrogen-bonding interactions with a different temperature dependence. The hydrogen-bond acidity of the SLB-IL60 column is unexpected since the stationary phase contains no hydrogen-bond acid groups and is not obviously connected to contributions from the deactivated column wall. The polarity number is shown to be a poor indicator of column retention properties. Principal component analysis with the system constants of the solvation parameter model as variables indicates that the properties of SLB-IL60 are not duplicated by any of the common poly(siloxane) and poly(ethylene glycol) stationary phase chemistries in common use for column preparation. The SLB-IL60 column has similar selectivity to a poly(cyanopropylphenyldimethylsiloxane) stationary phase containing 50% cyanopropylphenyl siloxane monomer but the two columns are not selectivity equivalent. Poly(ethylene glycol) stationary phases indicated as most similar to SLB-IL60 based on their polarity numbers are shown to have quite different selectivity.

Validation of QuEChERS based method for determination of fenitrothion residues in tomatoes by gas chromatography-flame photometric detector: Decline pattern and risk assessment.

A simple and rapid gas chromatography with flame photometric detector (GC-FPD) determination method was developed to detect residue levels and investigate the dissipation pattern and safe use of fenitrothion in tomatoes. A modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) using an ethyl acetate-based extraction, followed by a dispersive solid-phase extraction (d-SPE) with primary-secondary amine (PSA) and graphite carbon black (GCB) for clean up, was applied prior to GC-FPD analysis. The method showed satisfactory linearity, recovery and precision. The limits of detection (LOD) and quantification (LOQ) were 0.005 and 0.01mg/kg, respectively. The residue levels of fenitrothion were best described by first order kinetics with a half-life of 2.2days in tomatoes. The potential health risks posed by fenitrothion were not significant, based on supervised residue trial data. The current findings could provide guidance for safe and reasonable use of fenitrothion in tomatoes and prevent health problems to consumers.

Comparison of the performance of forward fill/flush and reverse fill/flush flow modulation in comprehensive two-dimensional gas chromatography.

The performances of forward flow fill and flush (FFF) and of reverse flow fill and flush (RFF) in flow modulated comprehensive two-dimensional gas chromatography (GC×GC) using the same volume of the sampling channel have been studied and compared. Sample models include a reference mixture of hydrocarbons at low concentration, a petroleum reformate product and the essential oil of Rosa damascena Miller. The latter samples contain solutes in different concentrations but some up to 30% allowing to study overloading phenomena in detail. For solutes injected at low quantity, the performance of FFF and RFF is similar. For solutes present in a sample at high quantity, RFF guarantees less broadening and spreading resulting in better quantitation.

An improved back-flush-to-vent gas chromatographic method for determination of trace permanent gases and carbon dioxide in ultra-high purity ammonia.

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 NaHSO4 ammonia trap is described. The NaHSO4 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.