Spectrometry Selected Ion Monitoring Research Articles

Gas chromatography-mass spectrometry selected ion monitoring and gas chromatography-tandem mass spectrometry selected reaction monitoring analyses of mono-, di- and tri-unsaturated C25 highly branched isoprenoid alkene biomarkers in sea ice and sediment samples: A comparative study.

The efficiency of selected ion monitoring (SIM) and selected reaction monitoring (SRM) analyses for the quantification of three mono-, di- and tri-unsaturated highly branched isoprenoid (HBI) alkenes (IP25 , IPSO25 and HBI III, respectively), often used as proxies for the occurrence of Arctic and Antarctic sea ice or the adjacent open waters, was compared. Gas chromatography (GC)-mass spectrometry (MS)/SIM and GC/MS/MS/SRM analyses were carried out on dilute solutions made from purified standards of these three HBIs, and then on hydrocarbon fractions of several sediment and sea ice sample extracts. More efficient and specific SRM transitions were selected after collision-induced dissociation of each precursor ion at different collision energies. SRM analysis avoided any overestimation of IP25 resulting from the contribution of the coeluting 13 C mass isotopomer of IPSO25 (M+ ˙ + 2) to the SIM target ion. In contrast, SRM analysis is less reliable for IPSO25 quantification in cases where several regio-isomers are present, likely due to intense double bond migrations following electron impact. In the case of HBI III, SRM analysis constitutes a potentially suitable alternative to SIM analysis, especially in terms of improving limit of detection. Despite the intense migrations of HBI double bonds under electron ionization, the selected SRM transitions should be more suitable than SIM target ions for IP25 and HBI III quantification in complex hydrocarbon fractions of natural samples. However, the advantage is less evident for IPSO25 due to the presence of numerous regio-isomers.

Exposure assessment of polycyclic aromatic hydrocarbons in refined coal tar sealant applications.

Refined coal tar sealant (RCTS) emulsions are used to seal the surface of asphalt pavement. Nine of the 22 polycyclic aromatic hydrocarbons (PAHs) evaluated in this study are classified as known, probable, or possible human carcinogens. Exposure assessment research for RCTS workers has not been published previously. The overall objective of this study was to develop a representative occupational exposure assessment of PAH exposure for RCTS workers based on worksite surveys. The specific aims were to: 1) quantify full-shift airborne occupational exposures to PAHs among RCTS workers; 2) quantify workers' dermal exposures to PAHs; 3) quantify biomarkers of PAH exposure in workers' urine; 4) identify specific job titles associated with RCTS exposure; and 5) apply these results to a biological exposure index to assess risk of potential genotoxicity from occupational exposures. A total of twenty-one RCTS workers were recruited from three companies. Personal and area air samples were collected using a modification of NIOSH Method 5515. Dermal exposure was assessed by hand and neck wipes before and after shifts. Twenty-two PAHs were quantified via gas chromatography-mass spectrometry selected ion monitoring. Internal dose was estimated by quantifying select PAH metabolites in pre- and post-shift urine samples using on-line solid phase extraction-high performance liquid chromatography-tandem mass spectrometry. PAH levels in the worker breathing zones were highest for naphthalene, acenaphthene, and phenanthrene, with geometric means of 52.1, 11.4, and 9.8μg/m3, respectively. Hand wipe levels of phenanthrene, fluoranthene and pyrene were the highest among the 22 PAHs with geometric means of 7.9, 7.7, and 5.5μg/cm2, respectively. Urinary PAH biomarkers for naphthalene, fluorene, phenanthrene, and pyrene were detected in all workers and were higher for post-shift samples than those collected pre-shift. Urinary concentrations of the metabolite 1-hydroxypyrene were greater than the American Conference of Governmental Industrial Hygienists (ACGIH) Biological Exposure Index (BEI) for this metabolite in 89 percent of post-shift samples collected on the final day of the work week or field survey. Statistically significances were found between concentrations of fluorene, naphthalene, and phenanthrene in the breathing zone of workers and their corresponding urinary PAH biomarkers. Workers were placed in two work place exposure groups: applicators and non-applicators. Applicators had higher total PAH concentrations in personal breathing zone (PBZ) air samples than non-applicators and were more likely to have post-shift hand wipe concentrations significantly higher than pre-shift concentrations. Concentrations of post-shift urinary biomarkers were higher, albeit not significantly, for applicators than non-applicators. The exposure results from RCTS worker samples cannot be explained by proximal factors such as nearby restaurants or construction. Air and skin concentration levels were substantially higher for RCTS workers than previously published levels among asphalt workers for all PAHs. PAH profiles on skin wipes were more consistent with RCTS sealant product than air samples. Last day post-shift urinary concentrations of 1-hydroxypyrene greatly exceeded the ACGIH BEI benchmark of 2.5μg/L in 25 of 26 samples, which suggests occupational exposure and risk of genotoxicity. When pyrene and benzo[a]pyrene were both detected, concentration ratios from personal exposure samples were used to calculate the adjusted BEI. Concentrations of 1-hydroxypyrene exceeded the adjusted BEIs for air, hand wipes, and neck wipes in most cases. These results indicate the need to increase safety controls and exposure mitigation for RCTS workers.

GC/EI-MS method for the determination of phytosterols in vegetable oils

Sterols are a highly complex group of lipophilic compounds present in the unsaponifiable matter of virtually all living organisms. In this study, we developed a novel gas chromatography with mass spectrometry selected ion monitoring (GC/MS-SIM) method for the comprehensive analysis of sterols after saponification and silylation. A new referencing system was introduced by means of a series of saturated fatty acid pyrrolidides (FAPs) as internal standards. Linked with retention time locking (RTL), the resulting FAP retention indices (RIFAP) of the sterols could be determined with high precision. The GC/MS-SIM method was based on the parallel measurement of 17 SIM ions in four time windows. This set included eight molecular ions and seven diagnostic fragment ions of silylated sterols as well as two abundant ions of FAPs. Altogether, twenty molecular ions of C27- to C31-sterols with 0–3 double bonds were included in the final method. Screening of four common vegetable oils (sunflower oil, hemp oil, rapeseed oil, and corn oil) enabled the detection of 30 different sterols and triterpenes most of which could be identified.Graphical abstract

Serum 4\u03b2-hydroxycholesterol increases during fluconazole treatment

PurposeThe antifungal drugs ketoconazole and itraconazole reduce serum concentrations of 4β-hydroxycholesterol, which is a validated marker for hepatic cytochrome P450 (CYP) 3A4 activity. We tested the effect of another antifungal triazole agent, fluconazole, on serum concentrations of different sterols and oxysterols within the cholesterol metabolism to see if this inhibitory reaction is a general side effect of azole antifungal agents.MethodsIn a prospective, double-blind, placebo-controlled, two-way crossover design, we studied 17 healthy subjects (nine men, eight women) who received 400 mg fluconazole or placebo daily for 8 days. On day 1 before treatment and on day 8 after the last dose, fasting blood samples were collected. Serum cholesterol precursors and oxysterols were measured by gas chromatography-mass spectrometry-selected ion monitoring and expressed as the ratio to cholesterol (R_sterol).ResultsUnder fluconazole treatment, serum R_lanosterol and R_24,25-dihydrolanosterol increased significantly without affecting serum cholesterol or metabolic downstream markers of hepatic cholesterol synthesis. Serum R_4β-, R_24S-, and R_27-hydroxycholesterol increased significantly.ConclusionFluconazole inhibits the 14α-demethylation of lanosterol and 24,25-dihydrolanosterol, regulated by CYP51A1, without reduction of total cholesterol synthesis. The increased serum level of R_4β-hydroxycholesterol under fluconazole treatment is in contrast to the reductions observed under ketoconazole and itraconazole treatments. The question, whether this increase is caused by induction of CYP3A4 or by inhibition of the catabolism of 4β-hydroxycholesterol, must be answered by mechanistic in vitro and in vivo studies comparing effects of various azole antifungal agents on hepatic CYP3A4 activity.

Determination of Residual Chlorothalonil in Textiles

An effective method was established to determine the content of residual chlorothalonil in textiles by gas chromatography/mass spectrometry-selected ion monitoring coupled with ultrasonic extraction technique. Residual chlorothalonil in textiles was ultrasonically extracted using ethyl acetate as the extraction solvent. The extract was condensed and analyzed by gas chromatography/mass spectrometry in selected ion monitoring mode (GC/MS-SIM). The concentration of chlorothalonil was calibrated by the external standard method. Good linearity existed between the peak area and the mass concentration of chlorothalonil in the mass concentration range from 0.2 μg/mL to 42.8 μg/mL. The equation was A = 95,399ρ ? 50,848, with a correlation coefficient of 0.9999. The limit of detection was 0.1 mg/kg for chlorothalonil. The blank samples were spiked at three concentration levels, and the spiked average recoveries changed from 81.9% to 95.4% while the relative standard deviation (RSD) changed from 1.8% to 5.2%. The proposed method was simple, rapid, sensitive and the limit of detection could meet the limit requirements of relevant regulations. Commercially available textiles were measured by this method, and chlorothalonil at different concentration levels was detected in some samples.

Simultaneous analysis of eight benzodiazepines in blood and urine matrix by gas chromatography–mass spectrometry: Implications for air crash investigation

Introduction: Benzodiazepines are the most commonly prescribed class of drugs in India and are capable of impairing the performance of an aviator in therapeutic to subtherapeutic levels. Detection of benzodiazepines, particularly in blood, is not easy, since the concentrations present, especially following prescribed medical use, can be very low. Several publications have addressed estimation of benzodiazepines in plasma or serum; however, few have attempted their detection in whole blood. Urine, although a better specimen, benzodiazepines due to their extensive metabolism, its metabolites are excreted in urine instead of the parent compounds. Materials and Methods: In our laboratory, a method was developed for simultaneous detection and quantification of eight benzodiazepines in whole blood and urine matrix by gas chromatography–mass spectrometry selective ion monitoring (SIM) method. Chromatographic separation was optimized and achieved for separation of all 8 compounds using Agilent DB-5MS column. Retention time, selectivity and sensitivity were achieved by measuring each analyte in SIM mode. The developed method was tested and validated on actual biological samples for lorazepam, temazepam, diazepam, clonazepam, and nitrazepam. Conclusion: A single method was developed for the detection and quantification of eight benzodiazepines in whole blood and urine matrix by GC–MS SIM method. The method was also tested on limited number of actual biological samples for the lorazepam, temazepam, diazepam, clonazepam, and nitrazepam.

Determination of Acrylamide using Solid-phase Extraction and Gas Chromatography-Mass Spectrometry Selected Ion Monitoring in Roasted Cereal Foods

An analytical method has been developed for the determination of acrylamide in cereal-based foods. The method is based on extraction of acrylamide with water, cleaned up through a solid phase extraction (SPE) cartridge, followed by bromination of the acrylamide double bond. The reaction product (2,3-dibromopropionamide) is extracted with ethyl acetate and analyzed by gas chromatography coupled to mass spectrometry (GC/MS) in selected ion monitoring (SIM), employing acrylamide-2,3,3-d3 (AA-d3) as internal standard. The SPE process for sample preconcentration was performed on a commercially available SupelcleanTM Coconut Charcoal cartridge packed with active carbon. In this method, correlation coefficients (R2) of calibration curves appeared to be 0.9997 in the concentration range of 2.5~100 μg/kg. The method detection limit (MDL) and the limit of quantitation (LOQ) of acrylamide were 0.76 μg/kg and 2.32 μg/kg, respectively. The calibration curve showed good linearity above 0.9997 in the ranges of the 2.5~100 μg/kg. For validation purposes, recovery studies were carried out at one concentration levels (10 μg/kg, n=3). The intraday assay accuracy and precision were in the range 104% and 5.6%, respectively, and the interday assay accuracy and precision were in the range 95.8% and 5.3%, respectively. Key words: acrylamide, bromination, GC/MS, SPE, limit of quantitation (LOQ)

Determination of trace water contents of organic solvents by gas chromatography-mass spectrometry-selected ion monitoring

This paper describes the development of a novel gas chromatography-mass spectrometry-selected ion monitoring (GC/MS-SIM) method for the determination of trace water contents of organic solvents, using the characteristic m/z 18, m/z 17, and m/z 16 ions of H2O as the qualitative ion and the m/z 18 ion as the quantifier ion. The accuracy and precision of this method were validated. An excellent linear correlation was obtained for trace water contents between 0 and 0.5217 wt%, with a correlation coefficient (R2) of 0.9999, in addition to spike recoveries of 82.6–112.6%, and relative standard deviations (n = 6) of 0.4–7.2%. The limit of detection (S/N = 3) and limit of quantitation (S/N = 10) for the trace water contents of organic solvents were 0.0005% wt% and 0.0016% wt%, respectively.The analytical results confirmed that this method was useful for determining the trace water contents of organic solvents, because it has a low detection limit and wide linear range. It requires only small amounts of the samples and enables sample batch analysis. It is very environmentally friendly and saves reagents.

Determination of cembrenediols in tobacco by gas chromatography—mass spectrometry-selected ion monitoring with precolumn derivatization

An efficient and sensitive analytical method based on precolumn derivatization and gas chromatography—mass spectrometry—selected ion monitoring (GC—MS—SIM) was proposed and validated for analysis of two cembrenediols (CBDs) which are α-cembrenediol and β-cembrenediol in tobacco samples. CBDs in tobacco samples were extracted by sonication with 50 mL dichloromethane for 10 min before derivatized with 2:3 (v/v) bis(trimethylsilyl)trifluoroacetamide (BSTFA)—pyridine at 20 °C for 100 min. CBDs’ level in tobacco samples was analyzed by GC—MS—SIM and quantified by the internal standard method. The linear range for α-CBD and β-CBD was 13.6–554.6 μg mL−1 and 4.11–162.6 μg mL−1, and the correlation coefficients of both were 0.9998. The limit of detection (LOD) and limit of quantification (LOQ) of α-cembrenediol and β-cembrenediol were 0.40 μg g−1 and 1.34 μg g−1, and 0.27 μg g−1 and 0.90 μg g−1, respectively. Average recoveries of α-CBD and β-CBD were 94.4–99.9% and 91.9–98.2% while the relative standard deviations (RSDs, n = 5) were ranged from 2.67 to 5.6% and 2.04 to 4.22%, respectively. This proposed analytical method has been successfully applied to analyze CBDs in tobacco samples.

The significance of petroleum bitumen in ancient Egyptian mummies.

Mummification was practised in ancient Egypt for more than 3000 years, emerging from initial observations of buried bodies preserved by natural desiccation. The use of organic balms (and other funerary practices) was a later introduction necessitated by more humid burial environments, especially tombs. The dark colour of many mummies led to the assumption that petroleum bitumen (or natural asphalt) was ubiquitous in mummification; however, this has been questioned for more than 100 years. We test this by investigating 91 materials comprising balms, tissues and textiles from 39 mummies dating from ca 3200 BC to AD 395. Targeted petroleum bitumen biomarker (steranes and hopanes) analyses by gas chromatography-mass spectrometry selected ion monitoring (GC-MS SIM, m/z 217 and 191) showed no detectable bitumen use before the New Kingdom (ca 1550–1070 BC). However, bitumen was used in 50% of New Kingdom to Late Period mummies, rising to 87% of Ptolemaic/Roman Period mummies. Quantitative determinations using 14C analyses reveal that even at peak use balms were never more than 45% w/w bitumen. Critically, the dark colour of balms can be simulated by heating/ageing mixtures of fats, resins and beeswax known to be used in balms. The application of black/dark brown balms to bodies was deliberate after the New Kingdom reflecting changing funerary beliefs and shifts in religious ideology.This article is part of the themed issue ‘Quantitative mass spectrometry’.

Endogenous hormone concentrations correlate with fructan metabolism throughout the phenological cycle in Chrysolaena obovata.

Chrysolaena obovata, an Asteraceae of the Brazilian Cerrado, presents seasonal growth, marked by senescence of aerial organs in winter and subsequent regrowth at the end of this season. The underground reserve organs, the rhizophores, accumulate inulin-type fructans, which are known to confer tolerance to drought and low temperature. Fructans and fructan-metabolizing enzymes show a characteristic spatial and temporal distribution in the rhizophores during the developmental cycle. Previous studies have shown correlations between abscisic acid (ABA) or indole acetic acid (IAA), fructans, dormancy and tolerance to drought and cold, but the signalling mechanism for the beginning of dormancy and sprouting in this species is still unknown. Adult plants were sampled from the field across phenological phases including dormancy, sprouting and vegetative growth. Endogenous concentrations of ABA and IAA were determined by GC-MS-SIM (gas chromatography-mass spectrometry-selected ion monitoring), and measurements were made of fructan content and composition, and enzyme activities. The relative expression of corresponding genes during dormancy and sprouting were also determined. Plants showed a high fructan 1-exohydrolase (EC 3.2.1.153) activity and expression during sprouting in proximal segments of the rhizophores, indicating mobilization of fructan reserves, when ABA concentrations were relatively low and precipitation and temperature were at their minimum values. Concomitantly, higher IAA concentrations were consistent with the role of this regulator in promoting cell elongation and plant growth. With high rates of precipitation and high temperatures in summer, the fructan-synthesizing enzyme sucrose:sucrose 1-fructosyltransferase (EC 2.4.1.99) showed higher activity and expression in distal segments of the rhizophores, which decreased over the course of the vegetative stage when ABA concentrations were higher, possibly signalling the entry into dormancy. The results show that fructan metabolism correlates well with endogenous hormone concentrations and environmental changes, suggesting that the co-ordinated action of carbohydrate metabolism and hormone synthesis enables C. obovata to survive unfavourable field conditions. Endogenous hormone concentrations seem to be related to regulation of fructan metabolism and to the transition between phenophases, signalling for energy storage, reserve mobilization and accumulation of oligosaccharides as osmolytes.

A non-targeted gas chromatography/electron capture negative ionization mass spectrometry selected ion monitoring screening method for polyhalogenated compounds in environmental samples.

Many organohalogen compounds with adverse environmental properties have been detected in samples from marine ecosystems. Their quantitation is an important task in environmental analytical chemistry. However, the highly selective gas chromatography/mass spectrometry (GC/MS) selected ion monitoring (SIM) methods developed for this purpose only allow the detection of targeted compounds while unscreened compounds remain undiscovered. The detection of all polyhalogenated compounds in a sample requires the application of non-target methods. We present a simple quadrupole-based GC/ECNI-MS-SIM method in which the entire high mass range is screened in eight GC runs using three time windows. Recently developed in the GC/EI-MS mode, this approach has now been adapted to the more sensitive GC/ECNI-MS mode. With this method we analyzed a fraction of a dolphin blubber sample from Australia and a sponge sample from the Mediterranean Sea on polychlorinated and polybrominated compounds and compared the results with the corresponding GC/EI-MS measurements. The non-targeted GC/ECNI-MS-SIM chromatograms were clearly structured and hardly showed co-elutions. Altogether, >400 polyhalogenated compounds were detected in both samples. Many of them originated from unknown compounds. Several new or scarcely analyzed compounds could be tentatively identified. Most of the compounds were not detected with the non-target GC/EI-MS-SIM approach (~150 compounds detected). We also developed a two-dimensional plot in which the mass of the monoisotopic peak was plotted over the GC retention time and which was helpful for the identification of isomers. Since eight GC runs are required per sample, the method is not aimed for routine analysis. It is recommended as an initial screening method for the analysis of new sample matrices or samples from new regions. The non-targeted GC/ECNI-MS-SIM method benefits from the fact that it can be used with standard equipment.

Validation of an isotope dilution gas chromatography–mass spectrometry method for combined analysis of oxysterols and oxyphytosterols in serum samples

We describe the validation of a method for the analysis of oxysterols, i.e. oxycholesterols and oxyphytosterols, in human serum using gas chromatography–mass spectrometry selected ion monitoring (GC–MS-SIM). Concentrations of 7α- and 7β-hydroxy-, and 7oxo-cholesterol, -campesterol, and -sitosterol as well as 4β-hydroxycholesterol and side-chain oxygenated 24S-, 25-, and 27-hydroxycholesterol were determined by isotope dilution methodology.After saponification at room temperature the oxysterols were extracted, separated from their substrates, cholesterol, campesterol, and sitosterol, by solid phase extraction, and subsequently derivatised to their corresponding trimethylsilyl-ethers prior to GC–MS-SIM. In order to prevent artificial autoxidation butylated hydroxytoluene and ethylenediaminetetraacetic acid were added. The validation of the method was performed according to the International Conference on Harmonisation guidance, including limits of detection and quantification, ranges, recovery and precision. Due to improved instrumental settings and work-up procedure, limits of detection and quantification ranged between 8.0–202.0pg/mL and 28.0–674pg/mL, respectively. Recovery data in five calibration points varied between 91.9% and 116.8% and in serum samples between 93.1% and 118.1%. The mean coefficient of variation (CV) for the recovery of all compounds was <10%. Well satisfying CVs for within-day precision (2.1–10.8%) and for between-day precision (2.3–12.1%) were obtained. More than 20 samples could be processed in a single routine day and test series of about 300 samples can be realised without impairment of the validation parameters during a sequence. Comparison of oxysterol and oxyphytosterol content in serum and plasma revealed no difference.A fully validated isotope dilution methodology for the quantification of oxycholesterols and oxyphytosterols from human serum or plasma is presented.

Analysis of Cembranoids in Flue‐cured Tobacco by Accelerated Solvent Extraction and Gas Chromatography‐Mass Spectrometry‐Selected Ion Monitoring

AbstractAn efficient and sensitive analytical method based on accelerated solvent extraction (ASE) and gas chromatography‐mass spectrometry‐selected ion monitoring (GC‐MS‐SIM) was developed and validated for analysis of cembranoids in flue‐cured tobacco leaves. Extraction efficiency of different pretreatment methods including liquid‐solid extraction (LSE), ultrasound‐assisted extraction (UAE), Soxlet extraction and accelerated solvent extraction (ASE) was compared and ASE was chosen as the optimal extraction method. During ASE procedure, effect of four parameters on extraction efficiency was considered and the experimental conditions were selected as follows: extraction solvent: dichloromethane; oven temperature: 50 °C; static time: 5 min and number of cycles: 2. Working standards of cembranoids were isolated by silica gel column chromatography and the identification was performed by mass spectrometry. Performance characteristics such as linearity, limit of detection (LOD), limit of quantitation (LOQ), precision and recovery were studied. The LOD and LOQ values were ranging from 5.0 × 10−3 to 6.9 × 10−3 μg/mL and 1.7 × 10−2 to 2.3 × 10−2 μg/mL for all analytes. At three different spiked levels, recoveries for CBT‐ol, α‐CBT‐diol and β‐CBT‐diol were 94.6%‐105.1%, 93.0%‐97.2% and 88.7%‐107.5% while the relative standard deviations (RSDs) were in the ranges of 3.9%‐6.2%, 1.8%‐8.7% and 1.7%‐6.0%, respectively. The proposed analytical methodology was successfully applied in the analysis of cembranoids in tobacco samples.

Polyhydroxyalkanoate production from unexplored sugar substrates

Industrial-scale production of biopolymers is restricted by its elevated production costs in comparison with those associated with synthetic (no-biodegradable and no-biocompatible) polymers. In this study we tested for the first time two low-cost carbon substrates (i.e. carob pulp and fique juice) for lab-scale production of polyhydroxyalkanoate (PHA) with Bacillus megaterium. PHA detection and quantification was conducted by gas chromatography/mass spectrometry-selected ion monitoring (GC/MS-SIM). The results suggest that PHA production using carob pulp (from Hymenaea courbaril) may be as high as with sugar cane molasses. Moreover, it could serve for the synthesis of the most commercialized type of PHA (i.e. polyhydroxybutyrate; PHB) and/or other varieties (e.g. polyhydroxy-butyrate-co-valerate; PHBV) with different properties and potential applications.

Direct determination of flavor relevant and further branched-chain fatty acids from sheep subcutaneous adipose tissue by gas chromatography with mass spectrometry

4-Methyloctanoic acid, 4-ethyloctanoic acid and 4-methylnonanoic acid are key-flavor compounds of sheep and goat. Yet, the low amounts of these volatile branched-chain fatty acids (vBCFAs) in the fat of the ruminants hampered their determination on a routine basis. In this work we developed a gas chromatography/mass spectrometry selected ion monitoring (GC/MS-SIM) method for the direct determination of the vBCFAs as methyl esters, which were obtained after transesterification of subcutaneous adipose tissue of sheep. The excellent sensitivity of the GC/MS-SIM method (limit of quantification, LOQ, 3.6–4.8μg/g; limit of detection, LOD, 1.1–1.4μg/g for 4-Me-8:0, 4-Et-8:0 and 4-Me-9:0) enabled us to determine the three vBCFAs without an enrichment step. Subcutaneous adipose sheep tissue of three different breeds contained 23–88μg/g 4-methyloctanoic acid, 13–26μg/g 4-ethyloctanoic acid and ∼2.9–18μg/g 4-methylnonanoic acid. Since all fatty acids were present in the FAME fraction, the samples could be screened for further branched-chain FAMEs. After elimination of unsaturated fatty acids by hydrogenation (the presence of some unsaturated fatty acids could be verified by this measure), additional measurements in SIM and full scan modes of methyl esters and picolinyl esters enabled the determination of further 97 saturated fatty acids in the samples with eight to 20 carbons. The method is suited for routine analysis and may be useful to investigate the reasons for the abundance/absence of 4-methyloctanoic acid, 4-ethyloctanoic acid and 4-methylnonanoic acid and further branched-chain fatty acids in sheep and goat.

The relationships of phytosterols and oxyphytosterols in plasma and aortic valve cusps in patients with severe aortic stenosis

Phytosterols such as campesterol and sitosterol are susceptible to oxidation by reactive oxygen species. We hypothesize that the plant sterols (PS) campesterol and sitosterol and their 7-oxygenated metabolites (POPs) correlate within and between human plasma and aortic valve cusps tissues. Plasma and tissue concentrations of PS and POPs were analyzed by gas chromatography–mass spectrometry-selected ion monitoring. Prior to analysis valve cusps tissue was mechanically separated from the calcified parts. PS and POP levels per dry cusps tissue weight were significantly higher compared with the concentrations in the calcified part. Against our hypothesis we found that despite the fact that there is a high correlation between plant sterols in and between plasma and valves cusps tissue, as well as a high correlation between plant sterols and oxyphytosterols and oxyphytosterols themselves within the valve cusps tissue, there was hardly any correlation in the amount of oxyphytosterols in plasma and between plasma and valves. Because plasma samples are easily accessible for large scale population based studies, we have to understand in more detail what the analysis of POPs implies in terms of CVD risk for the future.

Application of TLC, HPLC and GC methods to the study of amino acid and peptide enantiomers: a review

Amino acids are very important organic compounds in nature. The biological activity of amino acids depends mainly on their stereoisomeric configuration (d- or l-). Thus, the stereochemical analysis of amino acids and peptides is an important aspect of their characterization. Owing to the increasing role of amino acid configuration in biomedical and pharmaceutical studies, numerous analytical methods have been described in the literature. Among a wide range of analytical techniques available for the steroselective separation of different amino acids, which were obtained from plants or biological samples, chromatographic methods such as thin-layer chromatography, high-performance chromatography and also gas chromatography are very useful. This review presents such systems developed for direct stereoisomeric separation and quantitative determination of amino acid and peptide enantiomers with emphasis on selected literature published during two last decades. Almost all aspects, including sample preparation prior chromatographic analysis, stationary phase, solvent system and detection system, are discussed. New possibilities in chiral amino acid analysis have been opened up by the application of mass spectrometry and infrared detection in thin-layer chromatography and mass spectrometry-selected ion monitoring detection system in gas chromatography. A modern trend in high-performance chromatography is two-dimensional chromatography. These innovations have led to decreased development time and increased amino acid resolution and detectability.

Fast Determination of Pyrethroid Pesticides in Tobacco by GC-MS-SIM Coupled with Modified QuEChERS Sample Preparation Procedure

An analytical method was developed for the extraction and determination of pyrethroid pesticide residues in tobacco. The modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method was applied for preparing samples. In this study, methyl cyanide (MeCN)-saturated salt aqueous was used as the two-phase extraction solvent for the first time, and a vortex shaker was used for the simultaneous shaking and concentration of the analytes. The effects of experimental parameters on extraction and clean-up efficiency were investigated and optimized. The analytes were determined by gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM). The obtained recoveries of the analytes at three different fortification levels were 76.85-114.1% and relative standard deviations (RSDs) were lower than 15.7%. The limits of quantification (LOQs) were from 1.28 to 26.6 μg kg(-1). This method was also applied to the analysis of actual commercial tobacco products and the analytical results were satisfactory.

Determination of Listeria Monocytogenes in Agricultural Products by-High Resolution Pyrolysis Gas Chromatography-Mass Spectrometry

A method was developed for the qualitative determination of Listeria monocytogenes in the agricultural products by high resolution pyrolysis gas chromatography-mass spectrometry-selected ion monitoring(HPRGC/MS-MIS) technology.The method was accurate,highly sensitive and easy to operate.The operation conditions of HRPGC/MS system were as follows: pyrolysis conditions were as follows: starting temperature was 50 ℃,heating rate was 20 ℃/min,the temperature of the pyrolysis room was 230 ℃,and pyrolysis temperature was 650 ℃ for 10 s.Gas chromatography was accomplished with a carrier gas of helium at a flow rate of 0.9 mL/min.The GC column was a DB-WAXTER capillary column.The GC column temperature initially was kept at 45 ℃ for 4 min,then programmed to 100 ℃ at 6 ℃/min,200 ℃ at 10 ℃/min,250 ℃ at 12 ℃/min and held for 25 min.The total flow rate was spilt at ratio of 50 to 1.EI was used as ion source.The retention time of 19.056 min was selected for SIM,the ions of m/z were 54,98.L.monocytogens,two kinds of agricultural products with and without L.monocytogens samples were evaluated by this method according to the characteristics of the selected ion of L.monocytogens.An expected result was observed using the HRPGC/MS to detect L.monocytogens in different kinds of food,cucumber and beef.This method does not need the complex pre-treatment,the analysis time was comparatively short,and handing is easy for the operator.Retention time and mass spectra were used for qualitative analysis at the same time to eliminate the interference of different kinds of agricultural product impurities.The accurateness,good selectivity and reproducibility of the results demonstrate that HRPGC/MS is a useful method for rapid detection of L.monocytogens in agricultural products.