GC-MS) And Gas Chromatography-tandem Mass Spectrometry Research Articles

GEOCHEMICAL CHARACTERISTICS OF CRUDE OILS FROM THE SHARARA‐C OIL FIELD, MURZUQ BASIN, SOUTHWESTERN LIBYA

Crude oil samples from the Sharara‐C oil field (Concession NC‐115, Murzuq Basin, SW Libya) were analysed by organic geochemical methods in order to infer the geochemical characteristics of their respective source rocks. Aromatic hydrocarbons were analysed by gas chromatography – mass spectrometry (GC‐MS), and gas chromatography – tandem mass spectrometry (GC‐MS‐MS) was used to analyse saturated biomarkers. The Sharara‐C oils are interpreted to have been generated by marine shales containing mixed terrigenous and marine organic materials deposited in an intermediate (suboxic) environment. Age‐specific biomarker ratios indicated that the oils are older than Cretaceous, and maturation‐related parameters pointed to their high thermal maturity. Consistent with previous studies, source rocks are inferred to be “hot” shales in the Lower Silurian Tanezzuft Formation.Almost all the parameter ratios calculated varied over a very narrow range, indicating that the investigated oils were compositionally similar. The only significant difference that was noted concerned the sterane/hopane ratios whose variation suggested that there was some variability in the composition of the source organic material.The organic geochemical parameters determined for the Sharara‐C crude oils were compared with published data on other crude oils from Concession NC‐115. Almost all the parameters agreed well with previously published data on oils from this part of the Murzuq Basin. The greatest deviation concerned the values of some of the maturity parameters. This tended to confirm the conclusions of previous studies concerning the presence of a number of distinct oil families and sub‐families in the Sharara oil field area which are genetically related but which have different maturities.

Biomarkers in Source Rocks from Barreirinha Formation (Devonian): Distribution and Paleoenvironment Significance

The Barreirinha Formation-Upper Devonian, is the main petroleum source rock of the Amazon Basin, deposited during the great Devonian Transgression, contributing to significant accumulations of organic matter (OM) in anoxic conditions, which allowed its preservation. The present work had the objective of characterizing the molecular composition of biomarkers in outcrops samples of the Barreirinha Formation, aiming to evaluate the paleoenvironment, thermal evolution, and the preservation of OM total organic carbon (TOC) and Rock-Eval pyrolysis indicate considerable amounts of immature OM deposited in a low oxygenation environment. Gas chromatographymass spectrometry (GC-MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS) data corroborate that the OM was deposited in a suboxic to the oxic environment and low salinity (absence or low relative abundance of β-carotane and gammacerane). 24-N-Propyl-cholestane was detected and identified by synthetic pattern co-injection. High concentrations of tetracyclic polyprenoids (TPPs) in ascending order from base to top, high hopane/sterane ratios, to suggest that the samples had a high molecular weight n-alkanes, C29 steranes, low thermal evolution, and anoxic depositional paleoenvironment.

Understanding the relative performance of SCAN, SIM, PMRM and MRM methods for quantifying polycyclic aromatic hydrocarbons in crude oil samples.

Polycyclic aromatic hydrocarbons (PAHs) present in oil spill samples are analyzed by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/tandem mass spectrometry (GC/MS/MS) using four different methods: (1) full scan (SCAN), (2) selected ion monitoring (SIM), (3) multiple reaction monitoring (MRM), and (4) pseudo multiple reaction monitoring (PMRM). This study quantifies the relative performance of these methods. Novel experiments were designed to measure the signal-to-noise (S/N) ratios of all four methods. This was accomplished by spiking the crude oil with five deuterated PAHs (dPAHs) in two distinct ways: (1) varying the background noise by changing crude oil concentrations before spiking the samples with 1 ng/mL of dPAHs, and (2) varying the signal by spiking dPAHs concentrations of 0.5 and 5 ng/mL into a crude oil sample. The MRM method is the most selective and sensitive of the four methods. It also provides the lowest limit of detection (LOD) and limit of quantitation (LOQ). MRM is the optimal approach for quantifying PAHs in complex petroleum samples containing high levels of background noise. Also, our data show that the PAHs in complex oil spill samples can be quantified by MRM without using any complicated sample preparation steps. Based on our experimental data, the relative performance of the four methods used for quantifying PAHs in crude oil samples can be ranked as MRM > PMRM > SIM > SCAN.

Volatile organic compound analysis of accelerant detection canine distractor odours

Ignitable liquid detection dogs have been observed to falsely-respond to the pyrolysis products of common burned household items such as carpets and garden hoses, where ignitable liquids were not present. These responses from the canines are described as coming from distractor odours and decrease the reliability of detector dogs. The purpose of this research was to study the volatile organic compounds (VOCs) present in the odour profile of pyrolysed carpet and garden hose substrates, and determine whether a chemical similarity exists between these pyrolysis headspace profiles and target ignitable liquids, which may explain the false-positive behaviour of these detector dogs.Garden hose and carpet samples obtained from domestic settings were heated at a constant temperature for a specified time to produce pyrolysis products. A solid-phase microextraction (SPME) method was developed to extract the VOCs from burned substrates. The odours of the burned substrates were analysed by gas chromatography-mass spectrometry (GC/MS) and gas chromatography-tandem mass spectrometry (GC/MS/MS).A GC–MS/MS method was developed targeting the characteristic aromatic compounds in gasoline. Each pyrolysed substrate produced a complex and unresolved odour profile when analysed by GC- MS. GC–MS analysis failed to find any similarities between the odours of the burned substrates and ignitable liquids. GC–MS/MS analysis of pyrolysed garden hose and carpet substrate odours resolved and identified a wide range of aromatic target compounds – and these were present in high abundances in the hose samples. This indicates that there are significant chemical similarities between vapours of ignitable liquids and their distractor odours, which will have implications for the training of ignitable liquid detector dogs.

Organisation for the Prohibition of Chemical Weapons' New Approaches to Laboratory Support for Control over Non-Proliferation

The development of scientific research methods and dual-use production technologies, the widening of the range of new toxic chemicals, as well as technical possibilities for the development of a new generation of poisonous substances, formally not forbidden by the acting Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction, pose a new level of threats to nonproliferation of chemical weapons. Under these circumstances, it is necessary to possess not only legal possibility, but also appropriate laboratory equipment and services for the effective non-proliferation control. Considerable attention in this sphere has been paid earlier to environmental samples for toxic chemicals analysis, including samples of air, soil, vegetation and water. But at the present time the Organisation for the Prohibition of Chemical Weapons (OPCW) gives special emphasis to analysis of biomedical samples (blood, urine) in the context of non-proliferation and investigations of alleged use of chemical weapons and toxic chemicals. The proper sensitivity during the detection and identification of biomarkers of exposure to chemical agents and toxic chemicals can be achieved by gas chromatography- mass spectrometry (GC/MS) and gas chromatography-tandem mass spectrometry (GC/MS/MS) methods. Efforts in this sphere are now focused on three main tasks – sample preparation, the optimization of the conditions of chromatographic separation of samples, storage and interpretation of mass-spectra characteristics. The article provides examples of how the above mentioned techniques are used in the detection of signs and evidence of exposure to organic phosphorus compounds and sulfur mustard

3-Nitrotyrosine quantification methods: Current concepts and future challenges.

Measurement of 3-nitrotyrosine (3-NT) in biological samples can be used as a biomarker of nitrosative stress, since it is very stable and suitable for analysis. Increased 3-NT levels in biological samples have been associated with several physiological and pathological conditions. Different methods have been described for the detection and quantification of this molecule, such as (i) immunological methods; (ii) liquid chromatography, namely high-pressure liquid chromatography (HPLC)-based methods that use ultraviolet-visible (UV/VIS) absorption, electrochemical (ECD) and diode array (DAD) detection, liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS); (iii) gas chromatography, such as gas chromatography-mass spectrometry (GC-MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS). A literature review on nitrosative stress, protein nitration, as well as 3-NT quantification methods was carried out. This review covers the different methods for analysis of 3-NT that have been developed during the last years as well as the latest advances in this field. Overall, all methods present positive and negative aspects, although it is clear that chromatography-based methods present good sensitivity and specificity. Regarding this, GC-based methods exhibit the highest sensibility in the quantification of 3-NT, although it requires a prior time consuming derivatization step. Conversely, HPLC does not require such derivatization step, despite being not as accurate as GC. It becomes clear that all the methods described during this literature review, although accurate for 3-NT quantification, need to be improved regarding both sensitivity and specificity. Moreover, optimization of the protocols that have been described is clearly needed.

Detection and metabolic investigations of a novel designer steroid: 3-chloro-17α-methyl-5α-androstan-17β-ol.

In 2012, seized capsules containing white powder were analyzed to show the presence of unknown steroid-related compounds. Subsequent gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) investigations identified a mixture of 3α- and 3β- isomers of the novel compound; 3-chloro-17α-methyl-5α-androstan-17β-ol. Synthesis of authentic reference materials followed by comparison of NMR, GC-MS and gas chromatography-tandem mass spectrometry (GC-MS/MS) data confirmed the finding of a new 'designer' steroid. Furthermore, in vitro androgen bioassays showed potent activity highlighting the potential for doping using this steroid. Due to the potential toxicity of the halogenated steroid, in vitro metabolic investigations of 3α-chloro-17α-methyl-5α-androstan-17β-ol using equine and human S9 liver fractions were performed. For equine, GC-MS/MS analysis identified the diagnostic 3α-chloro-17α-methyl-5α-androstane-16α,17β-diol metabolite. For human, the 17α-methyl-5α-androstane-3α,17β-diol metabolite was found. Results from these studies were used to verify the ability of GC-MS/MS precursor-ion scanning techniques to support untargeted detection strategies for designer steroids in anti-doping analyses. Copyright © 2015 John Wiley & Sons, Ltd.

Detection of formestane abuse by mass spectrometric techniques.

Formestane (4-hydroxy-androstenedione) is an aromatase inhibitor prohibited in sports and included, since 2004, in the list of prohibited substances updated yearly by the World Anti-Doping Agency (WADA). Since the endogenous production of formestane has been described, it is mandatory for the anti-doping laboratories to use isotope ratio mass spectrometry (IRMS) to establish the exogenous origin before issuing an adverse analytical finding. The described IRMS methods for formestane detection are time-consuming, requiring usually two consecutive liquid chromatographic sample purifications in order to have final extracts of adequate purity before the mass spectrometric analysis. After establishing a procedure for the determination of the origin of formestane by IRMS without the need of derivatization, and integrated in the overall analytical strategy of the laboratory for pseudo-endogenous steroids, a mass spectrometric analysis by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS) of formestane metabolites was carried out in order to investigate whether other biomarkers of formestane abuse could be integrated in order to avoid time-consuming and expensive IRMS confirmations for formestane. From the metabolic studies performed, the inclusion of 3β,4α-dihydroxy-5α-androstan-17-one (4α-hydroxy-epiandosterone) in the routine GC-MS procedures has demonstrated to be diagnostic in order to reduce the number of unnecessary confirmations of the endogenous origin of formestane.

GC-MS and GC-MS/MS measurement of the cardiovascular risk factor homoarginine in biological samples.

L-Homoarginine (hArg) has recently emerged as a novel cardiovascular risk factor and to herald a poor prognosis in heart failure patients. Here, we report on the development and thorough validation of gas chromatography-mass spectrometry (GC-MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS) methods for the quantitative determination of hArg in biological samples, including human plasma, urine and sputum. For plasma and serum samples, ultrafiltrate (10µL; cutoff, 10kDa) was used. For urine samples, native urine (10µL) was used. For sputum, protein precipitation by acetone was performed. hArg is derivatized to its methyl ester tri(N-pentafluoropropionyl) derivative; de novo synthesized trideutero-methyl ester hArg is used as the internal standard (IS). Alternatively, [guanidino-(15)N2]-arginine can be used as an IS. Quantitative analyses were performed after electron-capture negative-ion chemical ionization by selected-ion monitoring in GC-MS and selected-reaction monitoring in GC-MS/MS. We obtained very similar hArg concentrations by GC-MS and GC-MS/MS, suggesting that GC-MS suffices for accurate and precise quantification of hArg in biological samples. In plasma and serum samples of the same subjects very close hArg concentrations were measured. The plasma-to-serum hArg concentration ratio was determined to be 1.12±0.21 (RSD, 19%), suggesting that blood anticoagulation is not a major preanalytical concern in hArg analysis. In healthy subjects, the creatinine-corrected urinary excretion of hArg varies considerably (0.18±0.22µmol/mmol, mean±SD, n=19) unlike asymmetric dimethylarginine (ADMA, 2.89±0.89µmol/mmol). In urine, hArg correlated with ADMA (r=0.475, P=0.040); in average, subjects excreted in the urine about 17.5 times more ADMA than hArg. In plasma of healthy humans, the concentration of hArg is of the order of 2µM. hArg may be a low-abundance constituent of human plasma proteins. The GC-MS and GC-MS/MS methods we report in this article are useful to study the physiology and pathology of hArg in experimental and clinical settings.

An automated sample preparation for detection of 72 doping‐related substances

Automation of sample preparation procedures in a doping control laboratory is of great interest due to the large number of samples that have to be analyzed, especially in large events where a high throughput protocol is required to process samples over 24 h. The automation of such protocols requires specific equipment capable of carrying out the diverse mechanical tasks required for accomplishing these analytical methodologies, which include pipetting, shaking, heating, or crimping. An automated sample preparation procedure for the determination of doping-related substances by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS) analysis, including enzymatic hydrolysis, liquid-phase extraction and derivatization steps, was developed by using an automated liquid handling system. This paper presents a description of the equipment, together with the validation data for 72 doping-related compounds including extraction efficiency, evaluation of carry-over, interferences, and robustness. Validation was approached as a comparison between the results obtained using the manual protocol and the transferred automated one. The described methodology can be applied for sample preparation in routine anti-doping analysis with high sample throughput and suitable performance.

Mass spectrometric description of novel oxymetholone and desoxymethyltestosterone metabolites identified in human urine and their importance for doping control

The metabolism of two anabolic steroids - oxymetholone and desoxymethyltestosterone - was reinvestigated to identify new targets potentially valuable for the antidoping analysis. Excretion urine samples from the laboratory reference collection were used in this study. Following fractionation of the urinary extract by means of high performance liquid chromatography (HPLC), each fraction was subjected to gas chromatography-mass spectrometry (GC-MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS) analysis after trimethylsilylation. About 20 metabolites were found for desoxymethyltestosterone and more than 40 for oxymetholone, with many of them being isomeric compounds. In addition to the well-known reduced and hydroxylated metabolites, 18-nor-17,17-dimethyl and 18-nor-17-hydroxymethyl-17-methyl steroids were also identified. Having evaluated all the metabolites in terms of how long they could be detected, we suggest that 18-nor-2ξ,17β-hydroxymethyl-17α-methyl-5α-androst-13-en-3α-ol is an important marker of oxymetholone abuse. In case of desoxymethyltestosterone, better detectability could be achieved if 18-nor-17,17-dimethyl-5α-androst-13-en-2ξ,3α-diol is monitored. These novel metabolites could be detected using GC-MS/MS at least for 14 days after administration of these anabolic steroids compared to 5-7 days for previously reported metabolites.

Identifying and Quantifying Contaminants Contributing to Endogenous Analytes in Gas Chromatography/Mass Spectrometry

Contaminants from various sources including medical devices, laboratory materials and the environment, and analytical apparatus may contribute to their endogenous congeners at different stages of the analytical process. Here, an approach is reported for the identification and quantification of contaminating analytes in biological fluids by stable-isotope dilution gas chromatography/mass spectrometry (GC/MS) and gas chromatography/tandem mass spectrometry (GC/MS/MS) methods. This approach is based on the analysis of different sample volumes and determination of the peak area ratio (PAR) of the endogenous analyte to the stable-isotope labeled analogue serving as the internal standard. The PAR is obtained by selected-ion monitoring or selected-reaction monitoring of appropriate ions. Generation of PAR values that correlate inversely with the sample volume subjected to analysis reveals the existence of contamination. The extent of contamination is obtained by plotting the PAR of endogenous analyte to internal standard versus the reciprocal of the sample volume analyzed. Examples are given for uncontaminated and contaminated endogenous analytes in biological samples, including nitrite and nitrate analyzed by GC/MS, and the fatty acid metabolites oleic acid oxide, oleic acid ethanol amide, and arachidonic acid ethanol amide analyzed by GC/MS/MS. Dependence of the PAR of endogenous analyte to its internal standard upon derivatization time reveals a unique kind of contamination that was identified in the GC/MS analysis of nitrate in plasma as pentafluorobenzyl ester. This kind of contamination occurs at the latest stage of GC/MS analysis and cannot be controlled by reference to the internal standard.

Plasma and urinary markers of oral testosterone undecanoate misuse.

Orally administered testosterone undecanoate (TU), an anabolic, androgenic steroid, can potentially be abused by athletes. Indirect evidence for detecting oral TU intake could be deduced from the changes in steroid profile post-administration. Direct evidence could be obtained by detection of unchanged TU in plasma. To this end, both urinary and plasma steroid profiles of six healthy male subjects given a single oral dose of 120 mg of TU were studied by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/tandem mass spectrometry (GC/MS/MS). The increased concentration of glucuronidated testosterone in plasma appears to be the most characteristic sign of oral TU intake. The testosterone glucuronide (TG)/nonconjugated testosterone (T) ratio, TG/17-hydroxyprogesterone (17OHP) ratio, and TG/luteinizing hormone (LH) ratio were observed to be significantly elevated above their basal levels for 10 h, 10 h, and 6 h, respectively. Urinary ratios of TG/epitestosterone glucuronide (EG) were found to be higher than the cut-off value of 6 for the period 4 approximately 8 h post-administration, but only in three subjects. One subject failed to respond with respect to all of the above-mentioned indirect markers, as TG was not significantly increased in either plasma or urine. Unchanged TU was directly detected in plasma of all six subjects from 1 approximately 1.5 h to 4 approximately 6 h after oral TU intake by GC/MS/MS, providing unequivocal proof of exogenous testosterone intake. Distinct and complementary markers for detecting oral TU intake could be obtained from plasma and urine, respectively.

Analysis of estrogenic hormones in municipal wastewater effluent and surface water using enzyme‐linked immunosorbent assay and gas chromatography/tandem mass spectrometry

Although the estrogenic hormones 17 beta-estradiol and 17 alpha-ethinyl estradiol can be quantified in polluted waters by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/tandem mass spectrometry (GC/MS/MS), the compounds often are present at concentrations below detection limits. Enzyme-linked immunosorbent assays (ELISAs) provide a sensitive and robust means of quantifying estrogenic hormones in wastewater effluents and surface waters. Results from ELISA analysis of estrogenic hormones in secondary wastewater effluent indicate concentrations comparable to those that cause vitellogenesis in fish. Confirmatory analyses by GC/MS/MS are consistent with ELISA results. Effluent filtration, using sand filtration or microfiltration, removes approx. 70% of the hormones from secondary effluent, while advanced treatment, using reverse osmosis, removes more than 95% of hormones. The detection limits for estrogenic hormones are approx. 0.1 ng/L in wastewater effluent and 0.05 ng/L in surface water. The ELISA technique provides a relatively simple and practical method of assessing the fate of estrogenic hormones in engineered and natural systems.

Mass spectrometric analysis of N-carboxymethylamino acids as periodate oxidation derivatives of Amadori compounds application to glycosylated haemoglobin

Periodate oxidation of free and protein-bound Amadori compounds formed by the condensation of reducing sugars with primary amino groups generates, on acid hydrolysis, N-carboxymethyl derivatives of amino acids. The analysis of these modified amino acids may be used to estimate both the extent and the site of protein glycosylation. The present study describes the use of gas chromatography-mass spectrometry (GC/MS) and gas chromatographytandem mass spectrometry (GC/MS/MS) for the identification of the various N-carboxymethylamino acids. Application of this approach to the quantitation of N-carboxymethylvaline and N (ε) -carboxymethyllysine resulting from the oxidation of glycosylated haemoglobin is presented.