Resolution Gas Chromatography Research Articles

Brominated Dioxins in Egg, Broiler, and Feed Additives: Significance of Bioassay-Directed Screening for Identification of Emerging Risks in Food.

Food authorities aim to safeguard our food. This requires sensitive analyses to guarantee detection of both banned and regulated substances at low concentrations. At the same time, broad screening methods are needed to identify new emerging risks. For this purpose, effect-based bioassays combined with mass spectrometric analyses offer an advantage. During the regular monitoring of dioxins in agricultural products, a discrepancy was observed between the results of the DR CALUX (Dioxin-Responsive Chemical Activated Luciferase gene Expression) bioassay and the confirmatory gas chromatographic high resolution mass spectrometric (GC-HRMS) analysis in egg and broiler fat samples. The response in the bioassay was high, suggesting a clear exceedance of the maximum limits of dioxins in these samples, yet regulated dioxins or dl-PCBs were not detected by GC/HRMS analysis. Ultimately, a broad screening analysis using GC-HRMS resulted in the identification of 2,3,7,8-tetrabromo-dibenzofuran (2,3,7,8-TBDF) in both egg and broiler fat. To investigate the potential source of this brominated furan contaminant, different samples were analyzed: bedding material, poultry feed, feed additives (choline chloride and l-lysine), and seaweed. The poultry feed and feed additives all contained 2,3,7,8-TBDF. Using a feed-to-food transfer model, it became clear that the poultry feed was probably the source of 2,3,7,8-TBDF in broilers and eggs through a feed additive like L-lysine or choline chloride. This study underlines the importance of using a combination of effect-based screening assays with sensitive analytical methods to detect potential new and emerging risks.

Thiol-yne Click Post-Modification for the Synthesis of Chiral Microporous Organic Networks for Chiral Gas Chromatography.

Microporous organic networks (MONs) have shown great potential in diverse domains recently. However, the application of MONs in chiral separation or catalysis has been largely lagged due to the lack of chiral MONs and the challenge to synthesize chiral MONs. Here we report a facile thiol-yne click strategy to post-synthesize chiral MONs for the first application in chiral gas chromatography. Three chiral MONs with different chiral centers were rationally designed and synthesized to fabricate their capillary columns for gas chromatographic resolution of various chiral compounds with better resolution than three commercial chiral capillary columns. These results show the great potential of the thiol-yne click strategy for constructing newly chiral MONs and their application in chiral separation.

Automatic peak detection coupled with multivariate curve resolution–alternating least squares for peak resolution in gas chromatography–mass spectrometry

Gas chromatography–mass spectrometry (GCMS) has been extensively used in complex sample analysis for the high-throughput characterization of volatile and semivolatile compounds. However, the accurate extraction of compound information remains challenging. Here, we present a combined algorithm strategy for GCMS data analysis to accurately screen metabolites across groups. First, chromatographic peaks in a total ion chromatogram (TIC) are extracted by using a Gaussian smoothing strategy and aligned on the basis of their mass spectra by a dynamic programing algorithm. The aligned TIC peaks are then registered into a component list table by applying a nearest-neighbor clustering algorithm. Significantly expressed TIC peaks among groups are screened through statistical analysis, such as ANOVA. Second, a chemometric method of multivariate curve resolution–alternating least squares for the peak resolution of the screened TIC peaks is utilized to retrieve the chromatographic and mass spectral profiles of coeluted components. The developed strategy is employed for the analysis of standard and complex plant sample datasets. Results indicate that our methodology is comparable with several state-of-the-art methods that are widely used in GC–MS-based metabolomics.

GC–MS analysis of regioisomeric substituted N-benzyl-4-bromo-2,5-dimethoxyphenethylamines

The six N-(dimethoxybenzyl)-4-bromo-2,5-dimethoxyphenethylamine regioisomers are potential designer compounds related to the common NBOMe drug N-(2-methoxy)benzyl-4-bromo-2,5-dimethoxyphenethylamine (25B-NBOMe). These six compounds represent the incorporation of one additional methoxy-group into the common NBOMe molecular framework. The compounds were prepared from commercially available precursor materials and their electron ionization mass spectra (EI-MS) are quite similar yielding nearly identical fragment ions. The 2′,3′-dimethoxybenzyl regioisomer gave a unique fragment ion of significant abundance in the EI-MS at m/z 136. Baseline gas chromatographic resolution of the six regioisomers was achieved using a midpolarity phase of 50% phenyl and 50% dimethyl polysiloxane and the more crowded dimethoxy substitution patterns eluted first under temperature programming conditions.The EI mass spectra for the TFA-derivatives of these six regioisomers gave a molecular ion of significant abundance at m/z 505/507, unlike the parent compounds. Differentiation and specific identification of all six of the regioisomers was possible based on a combination of different base peak ions (m/z 151 or 242/244), unique fragment ions (m/z 136 and m/z 263), along with differences in the relative abundance of ions at m/z 121 and m/z 91.

Risk characterisation from the presence of environmental contaminants and antibiotic residues in wild and farmed salmon from different FAO zones

ABSTRACTSalmon consumption is increasing year by year. Salmon aquaculture is the fastest growing food production system in the world, and often uses feed mixed with antibiotics or other drugs. Feed can be also contaminated by environmental contaminants like persistent organic pollutants and organophosphorus pesticides that usually accumulate in fatty tissue, or emerging contaminants such as perfluoroalkyl substances (PFASs), that instead bioaccumulate in protein tissues. Therefore, there is the need to investigate the presence of antibiotics and environmental contaminants, with multi-class and multi-residue liquid chromatography-high resolution mass spectrometry and gas chromatography tandem mass spectrometry methods to monitor a broad spectrum of residues comparing between wild and farmed salmons. The presence of residues was encountered at a concentration range of 0.35–51.52 ng g−1 for antibiotics only in farmed salmon, 0.19–34.51 ng g−1 for PFASs and 0.26–9.01 ng g−1 for (polybrominated diphenyl ethers) PBDEs, and 0.19–5.91 ng g−1 for organochlorine pesticides with higher frequencies and concentrations in farmed fish. Finally, the risk deriving from salmon intake is low, being of minor concern only for PBDE 99 and perfluorooctanoic acid.

ChemInform Abstract: Enantioselective Gas Chromatography in Search of the Origin of Biomolecular Asymmetry in Outer Space

AbstractReview: [67 refs.

Enantioselective Gas Chromatography in Search of the Origin of Biomolecular Asymmetry in Outer Space

AbstractSince the pioneering work of Emanuel Gil‐Av and his associates at the Weizmann Institute of Science the direct gas chromatographic resolution of enantiomers has found its application in different fields of natural sciences, even expanding to space research and astrobiology. In these domains the resolution of chiral molecules of prebiotic relevance is of particular interest, since the determination of ratios between l‐ and d‐enantiomers within non‐terrestrial samples is assumed to shed light on the origin of biomolecular homochirality and the beginnings of life itself. According to an astrophysical scenario, the first molecular symmetry breaking event occurred upon irradiation of chiral organic molecules with circularly polarized light present in the interstellar medium. To examine this hypothesis, among others, chiral gas chromatographic stationary phases have been widely used to provide the differentiation of enantiomers in extracts of meteorites, samples of simulated interstellar ices and Mars soil analogues. Moreover several chiral capillary columns have been selected for in situ analyses of extraterrestrial organic matter by Mars missions and the cometary Rosetta mission. This review will highlight current advances of enantioselective gas chromatography applied to space science.

Gas Chromatography Coupled to Atmospheric Pressure Chemical Ionization FT-ICR Mass Spectrometry for Improvement of Data Reliability

Atmospheric pressure chemical ionization (APCI) offers the advantage of molecular ion information with low fragmentation. Hyphenating APCI to gas chromatography (GC) and ultrahigh resolution mass spectrometry (FT-ICR MS) enables an improved characterization of complex mixtures. Data amounts acquired by this system are very huge, and existing peak picking algorithms are usually extremely time-consuming, if both gas chromatographic and ultrahigh resolution mass spectrometric data are concerned. Therefore, automatic routines are developed that are capable of handling these data sets and further allow the identification and removal of known ionization artifacts (e.g., water- and oxygen-adducts, demethylation, dehydrogenation, and decarboxylation). Furthermore, the data quality is enhanced by the prediction of an estimated retention index, which is calculated simply from exact mass data combined with a double bond equivalent correction. This retention index is used to identify mismatched elemental compositions. The approach was successfully tested for analysis of semivolatile components in heavy fuel oil and diesel fuel as well as primary combustion particles emitted by a ship diesel research engine. As a result, 10-28% of the detected compounds, mainly low abundant species, classically assigned by using only the mass spectrometric information, were identified as not valid and removed. Although GC separation is limited by the slow acquisition rate of the FT-ICR MS (<1 Hz), a database driven retention time comparison, as commonly used for low resolution GC/MS, can be applied for revealing isomeric information.

Determination of polychlorinated biphenyls and organochlorine pesticides in small volumes of human blood by high-throughput on-line SPE-LVI-GC-HRMS

A fully automated and robust method featuring on-line solid-phase extraction (SPE) and large volume injection (LVI) gas chromatographic (GC) high resolution mass spectrometry (HRMS) is used to determine polychlorinated biphenyls (PCBs) and organochlorine pesticides, such as penta- and hexachlorobenzene (PeCBz, HxCBz), hexachlorocyclohexane isomers (HCH) and 4,4'-dichlorodiphenyldichloroethene (a metabolite of dichlorodiphenyltrichloroethane (DDT)), with only 200μl of human blood, serum or plasma. After spiking the sample with (13)C-labeled internal standards and precipitating the proteins, the sample is passed through a 10mm×2.0mm ID SPE cartridge filled with C18 material that adsorbs the analytes. After washing and drying, the cartridge is extracted with hexane/dodecane (99/1, v/v); the extract is directly injected into a LVI where GC/HRMS analysis follows. The fully automated system utilizes a robotic autosampler and a modular SPE system including two high-pressure syringe pumps, an automatic SPE cartridge exchanger unit and 6 switchable valves. All sample preparation steps are performed within 20min during the GC run of a previous sample, limiting the throughput with only the GC runtime. The contents are quantified using the isotope dilution method. Due to laboratory air contamination problems, we achieved LOQs of 0.017 (PeCBz), 0.009 (HxCBz), 0.007 (HCH), 0.016 (DDE), while for the six indicator PCBs, we achieved values of 0.030 (PCB-28), 0.044 (PCB-52), 0.024 (PCB-101), 0.009 (PCB-138), 0.015 (PCB-153) and 0.008 (PCB-180)μg/l serum. Under clean laboratory air conditions, these values may be improved. This method is recommended when high throughput is desirable and/or only small amounts of material are available, such as during studies involving children.

Analysis of arsenic species in fish after derivatization by GC–MS

The derivatization of organoarsenic compounds by different reagents like thioglycolates or dithiols and the subsequent analysis by GC–MS as a molecular specific technique was investigated and described. The possible derivatization reagents methyl- and ethylthioglycolate (TGM and TGE), 1,3-propane- and 1,5-pentanedithiol (PDT and PeDT), which transfer the polar and nonvolatile analytes dimethylarsenate (DMA), monomethylarsonate (MMA), arsenite and arsenate into volatile compounds, were evaluated. The application for real samples like fish material was also studied.In addition the gas chromatographic separation and resolution was optimized and experiments were carried out to determine the highest derivatization rates. Derivatization reagents were evaluated in terms of quantity and stability of the formed chemical species.All derivatization products were characterized by mass spectrometry in order to identify the separated arsenic species.The most efficient conversion of DMA and MMA was observed by using ethylthioglycolate as derivatization agent. Finally, the derivatization procedure and the GC–MS-method were validated to determine linearity, precision, selectivity, analytical limiting values and recoveries. For the proposed method a limit of detection (LOD) of 5.8pg for DMA and 14.0pg for MMA was found. The accuracy was established by comparing the mean value measured for DMA in the certified reference material BCR-627 (tuna fish) with the certified one.MMA was not quantified in marine samples due to its low content. In shrimp samples DMA was not detectable. For codfish a DMA-content of 0.20±0.004mgkg−1, for “Surströmming” an amount of 0.38±0.02mgkg−1 and for herring, which showed the highest amount of DMA, a content of 1.15±0.03mgkg−1 was determined.

Enhanced comprehensive two-dimensional gas chromatographic resolution of polychlorinated biphenyls on a non-polar polysiloxane and an ionic liquid column series

A total of 196 out of 209 polychlorobiphenyl (PCB) congeners were resolved using GC × GC–TOFMS with a non-polar/ionic liquid column series consisting of poly(50%- n-octyl-50%-methyl)siloxane and (1,12-di(tripropylphosphonium)dodecane bis(trifluoromethansulfonyl)amide) in the first and second dimension, respectively. It has been found that 13 PCB congeners overlap in five doublets (CB12 + CB13, CB62 + CB75, CB70 + CB76, CB97 + CB125 and CB153 + CB168) and one triplet (CB90 + CB101 + CB113). All toxic, “dioxin like” congeners were separated with no interferences from any PCB congener. The 109 PCBs present in Aroclor 1242 and the 82 PCBs present in Aroclor 1260 were resolved GC × GC–TOFMS analysis on this column set.

Distribution of polybrominated diphenyl ethers in breast milk from North China: Implication of exposure pathways

The breast milk concentrations of polybrominated diphenyl ethers (PBDEs; sum of eight congeners: BDE-28, 47, 99, 100, 153, 154, 183 and 209) were determined (by high resolution gas chromatographic high resolution mass spectrometry) in samples from primiparous women collected in 2006 in Tianjin, China. Dietary and lifestyle habits of the participants were obtained by questionnaires. The median total PBDE concentration (including BDE-28, 47, 99, 100, 153, 154, 183) was 2500 pg g −1 lipid weight, ranging from 1700 to 4500 pg g −1 lipid weight. These levels were in the same range as those from Europe and Japan but much lower than those from North America. The congener profile in China was also different from other countries. The contribution of BDE-28 was around 15%, much higher than any other country, implying that a different Penta-BDE formulation might be used in the Chinese market. The lower ratio of the sum of BDE-47, 99, and 100 to the sum of BDE-153 and 154 suggested that Octa-products were in more demand in China. A significant correlation was found between a woman’s PBDE concentration and the time she used electronic appliances (h/d). This implies that electronics are a potential source of PBDEs to people. Inhalation or ingestion of particulate matter (such as dust) may also be an important exposure pathway. There was no significant correlation between the PBDE concentration and the consumption of meat, fish, and milk. Further research is needed to determine the specific contribution of each exposure route and their health effects.

Evaluation of automated direct sample introduction with comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry for the screening analysis of dioxins in fish oil

An automated direct sample introduction technique coupled to comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (DSI-GC × GC/TOF-MS) was applied for the development of a relatively fast and easy analytical screening method for 17 polychlorinated dibenzo- p-dioxins/dibenzofurans (PCDD/Fs) and 4 non-ortho polychlorinated biphenyls (PCBs) in fish oil. Comparison of instrumental performance between DSI-GC × GC/TOF-MS and the traditional gas chromatographic high resolution mass spectrometric (GC-HRMS) method showed good agreement of results for standard solutions analyzed in blind fashion. Relatively high tolerance of the DSI technique for lipids in the final extracts enabled a streamlined sample preparation procedure that only required gel permeation chromatography (GPC) and solid-phase extraction (SPE) cleanup with graphitized carbon black. The sample size for the method was 2 g of cod liver oil, which achieved limits of quantitation (LOQs) of 0.019–7.8 pg/g toxic equivalent quotients for the individual PCDD/Fs. Lower detection limits can be achieved by using larger sample size and scaling up the sample preparation procedure, but this adds to the labor, time, solvent consumption, and expense of the approach. However, the streamlined method yielded 0.94 pg/g and 2.3 pg/g LOQs for 2,3,7,8-tetrachloro dibenzofuran (TCDF) and 3,3′,4,4′,5-pentachloro biphenyl (CB126), which were sufficiently low for regulatory monitoring of 2 g samples. Therefore, instead of congener specific analysis, this streamlined analytical screening method for TCDF and CB126 has the potential to monitor fish oil contaminated with dioxin and dioxin-like PCBs at or above current food safety limits. Acceptable recoveries for nearly all analytes at three different spiking levels in fish oil samples were achieved with good repeatability.

Gas Chromatography-Mass Spectrometry Analysis of Regioisomeric Ring Substituted Methoxy Methyl Phenylacetones

The methoxy methyl phenylacetones share an isobaric relationship (equivalent mass but different elemental composition) to the controlled precursor substance 3,4-methylenedioxyphenylacetone. The 10 methoxy methyl phenylacetones as well as the methylenedioxyphenylacetones show essentially equivalent mass spectra with major fragment ions at m/z 135 and 43. Those methoxy methyl phenylacetones with the methoxy group substituted ortho to the benzylic cation in the m/z 135 ion show a further fragmentation to lose formaldehyde (CH2O) and yield a significant ion at m/z 105. The loss of formaldehyde from the ortho methoxy benzyl cation was confirmed using commercially available regioisomeric 2-, 3-, and 4-methoxyphenylacetones. The 10 regioisomeric methoxy methyl phenylacetones were prepared from the appropriately substituted benzaldehydes. Complete gas chromatographic resolution of all ten regioisomeric ketones was obtained on a stationary phase containing modified beta-cyclodextrin. Using the cyclodextrin containing phase, the ortho methoxy-substituted ketones (K1-K4) eluted before the meta-methoxy-substituted ketones (K5-K8) and the para-methoxy-substituted ketones (K9-K10) showed the greatest affinity for the stationary liquid phase and eluted last. Complete separation of the 10 ketones was not obtained on Rtx-1 and Rtx-200 columns.

Improvement in the gas chromatographic resolution of petroselinate from oleate

AbstractIn the extraction of oils from seeds of the genus Coriandrum, GC separations of petroselinate from oleate often gave poor resolution of these two isomers. Oleic and petroselinic acids were esterified with a series of alcohols (methanol, ethanol, 1‐propanol, 2‐propanol, 2‐methyl‐1‐propanol, 1‐butanol, 3‐methyl‐1‐butanol, and 2‐ethyl‐1‐hexanol). GC resolution of the Δ6 from the Δ9 and Δ11 octadecenoates was examined for all ester derivatives on a polar phase column. The Δ6 and Δ9 isomers were unresolved as methyl esters; however, the 2‐ethyl‐1‐hexyl esters gave baseline separation of all three isomers under temperature programming conditions. When isothermal conditions were optimized for each ester, separation of these isomers was possible with good resolution values (&gt;89%) for all the alcohols except methanol, which had a partial resolution of 51%. The rates of esterification of all the alcohols were determined for reactions with both oleic acid and triolein using potassium hydroxide as the esterification catalyst. Methanol gave the largest rate constant in both acid and oil esterification reactions with a rate constant 10‐fold better than all of the other alcohols. Based on rates of reaction, resolution of petroselinate from oleate, and removal of residual alcohol, the ethyl ester derivative appears to be the best choice for seed oils containing petroselinic acid.

Identification of isomeric 4-nonylphenol structures by gas chromatography–tandem mass spectrometry combined with cluster analysis

The endocrine-disrupting effect of 4-nonylphenols (NP) formed from industrial detergents such as nonylphenol polyethoxylates is well known today. The technical mixture contains a great variety of 4-iso-nonylphenol isomers having different endocrine-disrupting activities. Currently used gas chromatography–mass spectrometry (GC–MS) protocols allow the detection of about 20 peaks, mostly co-eluting isomers. In the present study, Product Ion mass spectrometry obtained by ion trap technology enhanced the selectivity in NP detection resulting in improved gas chromatographic resolution as well as structure assignment of the isomers. The structure proposals of 4-nonylphenol isomers given were derived from GC–MS–MS data processed by multivariate statistics. The cluster analysis allowed the classification of NP due to common structural features that were reflected in the mass spectra. The fragmentation pathways of three reference NP isomers, 4-(1-ethyl-1,4-dimethylpentyl)phenol ( NP1), 4-(1,1,5-trimethylhexyl)phenol ( NP2) and 4-(1-ethyl-1,3-dimethylpentyl)phenol ( NP3), were investigated in more detail. They served as model compounds to aid the interpretation of spectra from unknown NP isomers. Structures of two groups of isomers, characterized by α-ethyl as well as α-propyl substituents, could be proposed.

Air separation on H-mordenite

The separation of air components, oxygen and nitrogen, to obtain oxygen-enriched mixtures was studied by molecular modeling, utilising the Grand Canonical Monte Carlo method. Since a good gas-chromatographic resolution between oxygen and nitrogen was obtained on acid mordenite, with oxygen eluted first, the differential adsorption of air components was studied on this porous material in selected ranges of pressures (120–200 kPa) and temperatures (300–383 K). The results, which show that an oxygen enrichment up to 80% can be obtained, cannot be explained only by the small molecular volume difference, but quadrupolar interactions must also be considered. These strong interactions between molecules and within the host change considerably the amount of sorbed molecules, which depends on the mixture pressure and composition and on the acidity of the sorbent as well.

Analytical improvements in irm-GC/MS analyses: Advanced techniques in tube furnace design and sample preparation

Peak resolution is an essential requirement for achieving accurate irm-GC/MS compound-specific isotope measurements. Obtaining accurate isotope data from petroleum extracts, in particular, has proven especially difficult due to co-elutions that typically comprise crude oil mixtures. New enhancements in peak resolution in irm-GC/MS analyses have been achieved by substituting a polyimide-coated glass capillary as the furnace reactor. The advantages of the design are significant, and include: (1) incorporation of a zero dead-volume combustion reactor, resulting in almost no loss in gas chromatographic peak resolution, equating to less compound interferences and more accurately measured isotope values and (2) use of direct capillary-to-capillary leak tight, zero dead-volume connections that reduce the incidence of leak problems generally encountered as a result of using fittings of substantially different sizes. In addition, improvements in analytical chromatography using size-exclusion techniques such as urea adduction and molecular sieving reduces the number of components in a sample, and have resulted in the acquisition of more accurate isotope data. Experiments comparing paraffin isotope measurements for whole oil samples to those of urea adducted samples of the same oil have shown that differences of 2‰ are not uncommon. Data from experiments with isotope standards indicate that urea adduction and molecular sieving techniques have no observable fractionation effect on the measurement of isotope values for paraffin components in these mixtures. Considering the intensive effort and expense in generating irm-GC/MS data, the use of relatively inexpensive chromatography techniques such as urea adduction and molecular sieving in isolating components of interest for accurate isotope analysis is justified.

Discrimination properties of tetraamidic branched selectors

A new class of tetraamidic selectors with arms derived from l-phenylalanine and spaced by a phenolic template was synthesized. These chiral compounds were used as stationary phases for analytical gas chromatographic resolution of racemic mixtures of volatile amino acid derivatives; 1H NMR titration experiments were also performed. The experimental gas chromatographic and 1H NMR data collected support the hypothesis of a cooperation of the two chiral arms in binding and recognition of amino acidic substrates.

Low-Temperature Treatment of Soybean (Glycine max) Isoflavonoid Aglycon Extracts Improves Gas Chromatographic Resolution

ADVERTISEMENT RETURN TO ISSUECommunicationNEXTLow-Temperature Treatment of Soybean (Glycinemax) Isoflavonoid Aglycon Extracts Improves Gas Chromatographic ResolutionGregeory P. FennerView Author Information Crop Science Department, North Carolina State University, Box 7620, Raleigh, North Carolina 27695-7620Cite this: J. Agric. Food Chem. 1996, 44, 12, 3727–3729Publication Date (Web):December 18, 1996Publication History Received14 August 1996Published online18 December 1996Published inissue 1 January 1996https://doi.org/10.1021/jf960614gCopyright © 1996 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views319Altmetric-Citations5LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (81 KB) Get e-AlertsSUBJECTS:Chromatography,Flavonoids,High-performance liquid chromatography,Impurities,Plant derived food Get e-Alerts