High-temperature Gas Chromatography-mass Spectrometry Research Articles

Characterization and determination of free phytosterols and phytosterol conjugates: The potential phytochemicals to classify different rice bran oil and rice bran

Phytosterols are important beneficial compounds found in rice bran (RB) and rice bran oil (RBO). Although relationships have been confirmed between the forms of phytosterols and their bioactivities, the analysis of different forms of phytosterols in RB and RBO has been lacking. In this study, high temperature gas chromatography-mass spectrometry (HTGC-MS) was combined with the single standard to determine multi-components (SSDMC) method to determine free sterols (FSs) and steryl glycosides (SGs) in RB and RBO. High-performance liquid chromatography (HPLC) was used to determine steryl ferulates (SFs). There was clear variation in the composition of FS, SF and SG, indicating that different forms of phytosterols can discriminate between different RB and RBO. The developed method may be also useful for the detection of other compounds of interest in oils, oil seeds or cereals.

Separation and identification of Fischer-Tropsch wax by high temperature gas chromatography-mass spectrometry

Fischer-Tropsch (FT) wax is an important material produced from FT synthesis reactions. In this study, an improved separation and identification method for FT wax by high temperature gas chromatography (HTGC) coupled with cold-on-column (without pretreatment) was developed. In our improved separation procedure, the carrier gas was changed to helium and a long chromatographic column was adapted for use at high temperature. The n-alkanes in FT wax were well separated from other unknown components and the heavy components with carbon numbers higher than C90 could be eluted. Unknown components of the FT wax fraction were confirmed as alkanes, alkenes and oxygenated compounds by using HTGC-mass spectrometry. These results improve our understanding of the FT synthesis process and increase our detailed knowledge of FT products.

Simultaneous Determination of Sildenafil, Tadalafil, and Vardenafil in Pharmaceutical Preparations by High-Temperature Gas Chromatography/Mass Spectrometry

Sildenafil (SD), tadalafil (TD), and vardenafil (VD) are drugs used to treat erectile dysfunction (ED). Pharmaceutical counterfeiting-related SD, TD, and VD compounds are becoming a critical problem due to their harmful side-effects. Especially, SD and TD are two major counterfeit ED drugs in South Korea. In this study, a new high-temperature gas chromatography/mass spectrometry (HTGC/MS) method was developed for the rapid determination of SD, TD, and VD in pharmaceutical preparations. A HT GC column was introduced for the rapid analysis of high molecular weight and high boiling point compounds. High-speed centrifugation led to shortened time for results. Calibration curves were linear (R2 ≥ 0.9972) over the concentration ranges of 12.5–100 µg mg−1 for TD and VD, and 25–175 µg mg−1 for SD. The intra- and inter-day precisions were within 7.5 %, while the intra- and inter-day accuracies ranged from –3.0 to 8.0 %. The limits of quantification were 0.7 µg mg−1 (SD and TD) and 0.13 µg mg−1 (VD). The recoveries were in the range of 87.3–102.4 %. The developed method was rapid and accurate both for routine quantitative measurement of SD, TD, and VD in pharmaceutical preparations as well as screening their suspected counterfeit compounds.

The Effects of Burning and Mold Growth on the Chemical Composition of Firelog Fuels.

Firelogs consist of a cellulosic material, such as sawdust or wood particles, and a combustible binder (fuel). Historically, the fuel typically consisted of a petroleum-based (paraffin) wax; however, some manufacturers now include vegetable oils in their firelog fuels. To determine fuel composition, fuels from various brands of firelogs were extracted and analyzed by high-temperature gas chromatography-mass spectrometry (HTGC-MS) and a GC-MS with a polar column specific for the analysis of fatty acid methyl esters (FAMEs). Firelogs were also burned, allowed to grow mold, and analyzed by GC-MS to determine the effects that burning and mold growth have on firelog fuel composition. Mold did not tend to preferentially degrade any of the fatty acids. Burning caused a decrease in the relative amount of all of the fatty acids present in the vegetable oil fuel, with a greater effect on unsaturated fatty acids than saturated ones.

High-temperature GC-MS-based serum cholesterol signatures may reveal sex differences in vasospastic angina

Alterations of cholesterol metabolism are responsible for vasospastic angina and atherosclerosis. To comprehensively evaluate cholesterol metabolism, 18 sterols, including cholesterol, 6 cholesteryl esters (CEs), 3 cholesterol precursors, and 8 hydroxycholesterols (OHCs), were simultaneously analyzed using hybrid solid-phase extraction (SPE) purification coupled to high-temperature gas chromatography-mass spectrometry (HTGC-MS). Methanol-based hybrid SPE increased the selective extraction, and HTGC resulted in a good chromatographic resolution for the separation of lipophilic compounds. The limits of quantification of cholesterol and CEs ranged from 0.2 to 10.0 μg/ml, while OHCs and cholesterol precursors ranged from 0.01 to 0.10 μg/ml. Linearity as the correlation coefficient was higher than 0.99 with the exception of cholesteryl laurate, myristate, oleate, and linoleate (r2 > 0.98). The precision (% coefficient of variation) and accuracy (% bias) ranged from 1.1 to 9.8% and from 75.9 to 125.1%, respectively. The overall recoveries of CEs ranged from 26.1 to 64.0%, and the recoveries of other sterols ranged from 83.8 to 129.3%. The cholesterol signatures showed sex differences in patients with vasospastic angina and may associate with 24-reductases. This technique can be useful for making clinical diagnoses and for an increased understanding of the pathophysiology of vasospastic angina.

Studies of long chain lipids in insects by high temperature gas chromatography and high temperature gas chromatography–mass spectrometry

The organic compounds occurring naturally on the cuticles (surfaces) of insects are important for insect communication, help to act as protective water barriers and are useful in chemical taxonomy. Typically the cuticular lipids are only studied by gas chromatography–mass spectrometry (GC–MS) of hexane or pentane extracts, so the normal limitations of GC–MS makes it perhaps unsurprising that compounds with more than about 35 carbon atoms have only rarely been reported. Here we show by high temperature (HT) GC and HTGC–MS of extracts of eleven species of insects from nine genera, that longer chain compounds are actually common. Wax esters and triacylglycerides are virtually ubiquitous in such extracts, but long chain (>C35) hydrocarbons also sometimes occur. Whilst the latter have occasionally been reported previously from mass spectrometry studies, the use of the HTGC combination with MS allowed even some isobaric isomers to be separated and thus more complete lipid distributions to be monitored. Since the physical properties of cuticular compounds depend on this composition of the mixtures, such differences may influence the water loss rates of the insects, amongst other effects. In addition, the high molecular weight compound profiles may allow species to be more easily differentiated, one from another. It would be interesting to apply these methods to examination of the cuticular lipids of insects on a more routine basis, ideally in combination with MALDI-TOF-MS and imaging methods.

Identification and quantification of polyfunctionalized hopanoids by high temperature gas chromatography–mass spectrometry

Hopanoids are triterpenoids produced mainly by bacteria, are ubiquitous in the environment, and have many important applications as biological markers. A wide variety of related hopanoid structures exists, many of which are polyfunctionalized. These modifications render the hopanoids too involatile for conventional gas chromatography (GC) separation, so require either laborious oxidative cleavage of the functional groups or specialized high temperature (HT) columns. Here we describe the systematic evaluation and optimization of a HT–GC method for the analysis of polyfunctionalized hopanoids and their methylated homologs. Total lipid extracts are derivatized with acetic anhydride and no further treatment or workup is required. We show that acid or base hydrolysis to remove di- and triacylglycerides leads to degradation of several BHP structures. DB-XLB type columns can elute hopanoids up to bacteriohopanetetrol at 350°C, with baseline separation of all 2-methyl/desmethyl homologs. DB-5HT type columns can additionally elute bacteriohopaneaminotriol and bacteriohopaneaminotetrol, but do not fully separate 2-methyl/desmethyl homologs. The method gave 2- to 7-fold higher recovery of hopanoids than oxidative cleavage and can provide accurate quantification of all analytes including 2-methyl hopanoids. By comparing data from mass spectra with those from a flame ionization detector, we show that the mass spectromet (MS) response factors for different hopanoids using either total ion counts or m/z 191 vary substantially. Similarly, 2-methyl ratios estimated from selected-ion data are lower than those from FID by 10–30% for most hopanoids, but higher by ca. 10% for bacteriohopanetetrol. Mass spectra for a broad suite of hopanoids, including 2-methyl homologs, from Rhodopseudomonas palustris are presented, together with the tentative assignment of several new hopanoid degradation products.

Quantification of blending of olive oils and edible vegetable oils by triacylglycerol fingerprint gas chromatography and chemometric tools

A reliable procedure for the identification and quantification of the adulteration of olive oils in terms of blending with other vegetable oils (sunflower, corn, seeds, sesame and soya) has been developed. From the analytical viewpoint, the whole procedure relies only on the results of the determination of the triacylglycerol profile of the oils by high temperature gas chromatography–mass spectrometry. The chromatographic profiles were pre-treated (baseline correction, peak alignment using iCoshift algorithm and mean centering) before building the models. At first, a class-modeling approach, Soft Independent Modeling of Class Analogy (SIMCA) was used to identify the vegetable oil used blending. Successively, a separate calibration model for each kind of blending was built using Partial Least Square (PLS). The correlation coefficients of actual versus predicted concentrations resulting from multivariate calibration models were between 0.95 and 0.99. In addition, Genetic algorithms (GA–PLS), were used, as variable selection method, to improve the models which yielded R2 values higher than 0.90 for calibration set. This model had a better predictive ability than the PLS without feature selection. The results obtained showed the potential of this method and allowed quantification of blends of olive oil in the vegetable oils tested containing at least 10% of olive oil.

Extractive ethoxycarbonylation in high-temperature gas chromatography–mass spectrometry based analysis of serum estrogens

A comprehensive gas chromatography–mass spectrometry (GC–MS)-based profiling was developed as a practical assay for quantification of 18 endogenous estrogens in serum samples. The present GC–MS method was conducted with the two-phase extractive ethoxycarbonlyation (EOC) of the phenolic hydroxy groups of estrogen with ethyl chlorformate combined with the non-polar n-hexane extraction. The subsequent perfluoroacylation of aliphatic hydroxy groups with pentafluoropropionyl anhydride (PFPA) was conducted. The serum samples were separated through a high temperature GC column (MXT-1) within an 8-min run and analyzed in selected-ion monitoring mode with good chromatographic properties for 18 estrogens as their EOC-PFP derivatives. The limit of quantification (LOQ) was 0.025–0.10 ng/mL for most estrogens analyzed except for E3 and 2-OH-E3 (0.5 ng/mL each). The devised method was found to be linear over a 10 3-fold concentration range with a correlation coefficient ( r 2 > 0.992), whereas the precision (% CV) and accuracy (% bias) ranged from 3.1 to 16.3% and from 93.5 to 111.1%, respectively. Decreased 2-methoxy-17β-estradiol levels were confirmed in patients with preeclampsia than healthy pregnant women. This technique can be used for a clinical diagnosis as well as understanding the pathogenesis in estrogen-related disorders.

Database-dependent metabolite profiling focused on steroid and fatty acid derivatives using high-temperature gas chromatography–mass spectrometry

BackgroundA database-dependent gas chromatography–mass spectrometry (GC–MS) based approach was developed for non-targeted metabolite profiling, focusing on 232 steroids, 24 fatty acids, 10 eicosanoids, 10 cannabinoids and 22 steroid-fatty acid esters in biological specimens. MethodsThis method, used to search for potent biomarkers in lipid metabolism, included MS based analysis combined with high-temperature gas chromatographic (HTGC) separation of biological metabolites, statistical clustering and an in-house database (DB) searching. ResultsThe HTGC technique showed better detectability of high lipophilic compounds, particularly steroid-fatty acid esters, which generally have poor chromatographic properties on a conventional GC column. The in-house DB search consisted of the retention index and mass spectrum corresponding to each compound selected. The method was applied to tissue samples obtained from cardiac hypertrophy-induced mice. Increased levels of palmitic, linoleic, oleic, and stearic acids and cholesterol were detected and identified. ConclusionsThis data-dependent non-targeted metabolite profiling technique could be more effective in biomarker studies associated with the steroid and lipid metabolism than commercially available DBs.

Comparison of Motor Oils Using High‐Temperature Gas Chromatography‐Mass Spectrometry

The analysis of motor oils has wide applications in the forensic science field from comparing lubricants transferred between an automobile and a victim or crime scene to differentiating the compositions of plastic explosives. In this study, 40 unused motor oils were analyzed and compared by high-temperature gas chromatography-mass spectrometry to determine the potential for oil individualization. Oil samples were also collected from the crankcase dipsticks of 30 cars. Twenty-six of these oils could be differentiated from each other based on visual comparisons of the unresolved envelope (baseline rise due to incomplete separation) and the resolved hydrocarbons in the raw total ion chromatograms (TICs) and smoothed TIC data. Four of these oils were analyzed as unknowns and were correctly related to the corresponding vehicle. The use of extracted ion profiles (EIPs) was explored as a means to further discriminate between the indistinct samples based on the polycyclic aromatic hydrocarbon (PAH) content. The research discussed in this paper demonstrated that differentiation of motor oils was possible by examining the TIC, smoothed TIC, and EIP data.

Differentiation of Composition C-4 Based on the Analysis of the Process Oil

Abstract United States military Composition C-4 explosive contains 91% cyclotrimethylene trinitramine (RDX), 5.3% dioctyl sebacate or adipate (DOS or DOA), 2.1% polyisobutylene (PIB), and 1.6% oil. The original military specification required low viscosity engine oil, but this has since been changed to a specially manufactured mineral oil, also called “process oil.” Differentiation of military and commercial Composition C-4 may be possible by analyzing the oil. In this study, samples of Composition C-4 were taken from various lots of U.S. military M112 demolition blocks from two commercially manufactured brands sold in the U.S. The oil and plasticizer were extracted with pentane, and the plasticizer was removed using silica solid phase extraction cartridges. The oil was then analyzed by high-temperature gas chromatography/mass spectrometry (HTGC/MS). Results indicated that HTGC/MS is an excellent discriminating technique for oil comparisons; however, differentiation of Composition C-4 is limited by manufacturer production and distribution practices.

High-temperature gas chromatography–mass spectrometry with glass capillary columns for the screening of natural products

High-temperature high resolution gas chromatography (HT-HRGC) and HT-HRGC coupled to mass spectrometry (HT-HRGC–MS) are powerful but relatively unexplored tools for the analysis of crude extracts and fractions of natural products. To illustrate the scope of the technique the direct characterization of several compounds, present in crude extracts of leaves and stems of Croton hemiargyreus Muell. Arg. var. hemiargyreus was undertaken, without derivatization or clean-up procedures. Both practical aspects and limitations of HT-HRGC and HT-HRGC–MS were evaluated resulting in a simple, straightforward and extremely powerful technique for the analysis of complex mixtures.

Elucidation of the composition of bovine milk fat triacylglycerols using high-performance liquid chromatography–atmospheric pressure chemical ionisation mass spectrometry

Bovine milk fat triacylglycerols (TAGs) have been characterised using high-performance liquid chromatography–atmospheric pressure chemical ionisation mass spectrometry (HPLC–APCI-MS) and high-temperature gas chromatography–mass spectrometry (GC–MS). The complex nature of the fat meant that prefractionation was necessary to provide simpler fractions for more detailed molecular analyses. Silica thin-layer chromatography gave rise to two fractions, one of which contained predominantly butyric acid containing TAGs. Gel permeation chromatography (GPC) gave rise to 16 fractions, which were subsequently analysed using HPLC–APCI-MS. Twelve of the GPC fractions were also analysed by high-temperature GC–MS using a capillary column coated with a polarisable stationary phase. TAGs present in the fractions were correlated with those in the chromatogram of the whole milk fat through retention time comparison and the use of mass chromatograms. In total, 120 TAGs were identified.

Characterisation of organic pollutants in textile wastewaters and landfill leachate by using toxicity-based fractionation methods followed by liquid and gas chromatography coupled to mass spectrometric detection

In the present work, the characterisation of toxic organic compounds present in complex mixtures like textile effluents and landfill leachates is proposed. The protocol developed for the wastewater characterisation is based on solid phase extraction (SPE) combined with toxicity-fractionation followed by high temperature-gas chromatography-mass spectrometry (HT-GC-MS) and liquid chromatography-mass spectrometry (LC-MS). In this work Daphnia magna was used as the target organism to identify the toxic compounds in the different fractions. The highest toxicity was observed in the fractions exhibiting log K ow (octanol–water partition coefficient) between 1.7 and 5.16. After SPE followed by GC-MS and LC-MS using atmospheric pressure chemical ionisation (APCI) the compounds identified in the more toxic fractions were bis(2-ethylhexyl)phthalate, dibutyl phthalate, alcohol decyclic alcohol polyethoxylated, disulphonate hydoxynaphthalene, nonylphenol polyethoxylated and nonylphenol isomers. In addition to the toxicity based fractionation, a sequential solid phase extraction protocol (SSPE) followed by LC-APCI-MS, LC-electrospray (ESI)-MS and ion-pair chromatography (IPC)-ESI-MS) was also applied to the raw samples in order to identify the major number of polar organic pollutants.

Systematic study of high molecular weight compounds in Amazonian plants by high temperature gas chromatography-mass spectrometry.

The fractions of hexane and dichloromethane extraction from marupá (Simaruba amara) and (Bertholletia excelsa) leaves were analyzed by HT-HRGC (high temperature high resolution gas chromatography) and HT-HRGC coupled to mass spectrometry (HT-HRGC-MS). Several compounds can be characterized including unusual high molecular weight compounds.

Application of high-temperature gas chromatography-mass spectrometry to the investigation of glycosidically bound components related to cashew apple (Anacardium occidentale L. Var. Nanum) volatiles.

Free and bound volatile components of a Brazilian cashew apple variety (Anacardium occidentale L. var. nanum) were obtained by simultaneous distillation-extraction (SDE) and XAD-2 adsorption. According to gas chromatography-mass spectrometry (GC-MS) analyses and retention indices, 62 free volatile constituents were characterized and quantified. They were esters (40%), terpenes (20%), hydrocarbons (14%), fatty acids (9%), aldehydes (8%), alcohols (3%), lactones (3%), ketones (1%), phenols (1%), and norisoprenoids (1%). The glycosidically bound volatile precursors were analyzed by high-temperature GC-MS, after room temperature silylation. Several conjugated alcohols and cinnamic acids were detected and reported as cashew apple glycosyl constituents for the first time.

Simultaneous determination of urinary androgen glucuronides by high temperature gas chromatography-mass spectrometry with selected ion monitoring

An efficient procedure is described for the simultaneous determination of 9 androgen glucuronides including androsterone, etiocholanolone, 11-ketoandrosterone, 11-ketoetiocholanolone, 11β-hydroxyandrosterone, 11β-hydroxyetiocholanolone, and dehydroepiandrosterone (DHEA) in 3-glucuronide form and dihydrotestosterone (DHT) and testosterone in 17-glucuronide form from urine specimens. The method involves solid-phase extraction of the urinary steroids using Serdolit PAD-1 resin, with subsequent conversion to methyl ester-trimethylsilyl (Me-TMS) ether derivatives for the direct analysis by gas chromatography-mass spectrometry (GC-MS) using high temperature MXT-1 (Silcosteel-treated stainless steel) capillary column. Upon split injection of Me-TMS steroids at 330°C into the MXT-1 capillary column initially maintained at 300°C then programmed to 322°C at 2°C/min, each androgen glucuronide was well separated in excellent peak shape. The characteristic ions at m/z 217 constituting the base peaks in the electron-impact (20 eV) mass spectra for most steroids permitted their sensitive detection by GC-MS with selected-ion monitoring (SIM), whereas base peak ion at m/z 271 was used for the SIM of dehydroepiandrosterone-3-glucuronide. The detection limits for SIM of most of the steroids were 15 pg except for the 3-glucuronides of 11-ketoandrosterone and 11-ketoetiocholanolone, which could be detected down to 20 pg. The SIM responses were linear with correlation coefficients varying from 0.981 to 0.993 in the concentration range of 20 to 3000 ng/ml for the androgens studied. When applied to urine samples, the present method allowed rapid screening for the 7 androgens in their glucuro-conjugated forms simultaneously with good overall precision and accuracy within the normal concentration ranges of 15.1 to 3124.6 ng/ml.

Identification of Isoquinoline alkaloids in crude extracts by high temperature gas chromatography-mass spectrometry

Crude ethanol extracts of leaves of Croton (Euphorbiaceae) species (C. hemiargyreus var. gymnodiscus, C. hemiargyreus var. hemiargyreus and C. echinocarpus) were analysed using on-column injection high temperature gas chromatography coupled with mass spectrometry. Several isoquinoline alkaloids were identified, including isocorydine, corydine, glaucine and laurelliptine as the principal constituents. The cold on-column technique proved to be appropriate for injection of these compounds. The technique is shown to be a valuable tool and an alternative technique to classical phytochemical procedures permitting the fast analysis of alkaloid mixtures without the need for (extensive) fractionation and derivatisation. Copyright © 1999 John Wiley & Sons, Ltd.

Characterization of organic pollutants in industrial effluents by high-temperature gas chromatography–mass spectrometry

The characterization of complex mixtures of organic contaminants present in industrial effluents is a well-known problem. The determination of individual target analytes depends very much on the analytical method used. In this article, the possibilities of using high-temperature gas chromatography–mass spectrometry (HT-GC–MS) are explored. In HT-GC–MS non-polar and medium-polarity phases can be operated at temperatures up to 370–420°C, allowing the analysis of high-molecular-weight compounds. So far, the applications of HT-GC have included the analysis of hydrocarbons up to C-100, lipids, sugars, and polyglycerols, but no data have been reported on the characterization of organic pollutants present in industrial effluents. The general sample handling approach reported here is based either on a sequential solid-phase extraction (SSPE) procedure, with a change of solvent composition in the elution from two different cartridges (C18 and Lichrolut EN), or on a toxicological fractionation. Effluent samples from tanneries, petrochemical plants, and textile industries are characterized, and the levels of the main organic pollutants identified are indicated. More than 50 compounds, including n-alkanes, phthalates, esters, acids, and phenols, were identified in the effluents studied.