Use Of Gas Chromatography Research Articles

Determination of the concentration profile and homogeneity of antioxidants and degradation products in a cross-linked polyethylene type A (PEXa) pipe

A solvent extraction technique has been developed to determine the concentration profile of two antioxidants and five degradation products of antioxidants in cross-linked polyethylene (PEX) materials. Irganox ® 1076 and two degradation products in a PEX pipe type A (PEXa) were detected after extraction in chloroform. Fick's second law of diffusion was used to verify that 24 h of extraction at room temperature was sufficient to extract Irganox ® 1076 and the degradation products from PEX materials with a thickness of 5 μm. With the use of gas chromatography and mass spectrometry, the concentration profile was measured at four different places on a 100 m PEXa pipe. A two-way ANOVA analysis showed that the composition of Irganox ® 1076 was homogenous in the radial direction and heterogeneous in the longitudinal direction. Two degradation products of antioxidants were detected, 2,6-di- tert-butyl- p-benzoquinone and 2,4-di- tert-butyl phenol. The composition of 2,6-di- tert-butyl- p-benzoquinone was found to be homogeneous in the radial and longitudinal direction. 2,4-Di- tert-butyl phenol was homogeneous in the radial direction but heterogeneous in the longitudinal direction.

Evaluation of ionization techniques for mass spectrometric detection of contact allergenic hydroperoxides formed by autoxidation of fragrance terpenes

Hydroperoxides formed by autoxidation of common fragrance terpenes are strong allergens and known to cause allergic contact dermatitis (ACD), a common skin disease caused by low molecular weight chemicals. Until now, no suitable methods for chemical analyses of monoterpene hydroperoxides have been available. Their thermolability prohibits the use of gas chromatography and their low UV-absorption properties do not promote sensitive analytical methods by liquid chromatography based on UV detection. In our study, we have investigated different liquid chromatography/mass spectrometry (LC/MS) ionization techniques, electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI), for detection of hydroperoxides from linalool and limonene.Flow injection analysis was used to evaluate the three different techniques to ionize the monoterpene hydroperoxides, linalool hydroperoxide and limonene hydroperoxide, by estimating the signal efficacy under experimental conditions for positive and negative ionization modes. The intensities for the species [M+H]+ and [M+H-H2O]+ in positive ionization mode and [M-H]- and [M-H-H2O]- in negative ionization mode were monitored. It was demonstrated that the mobile phase composition and instrumental parameters have major influences on the ionization efficiency of these compounds. ESI and APCI were both found to be appropriate as ionization techniques for detection of the two hydroperoxides. However, APPI was less suitable as ionization technique for the investigated hydroperoxides.

Gas chromatography–mass spectrometric analysis of products from on-line pyrolysis/silylation of plant gums used as binding media

Plant gums are complex polysaccharides used in the field of cultural heritage especially as binding media. Classification of polysaccharides may be achieved on the basis of monosaccharides composition after cleavage of glycosidic bond. Characterization of plant gums in works of art is complicated by the necessity of to use a method minimally invasive and requiring a small mount of sample. Pyrolisys is an useful method to obtain polysaccharides decomposition and generally pyrolysis products can be identified by the use of gas chromatography–mass spectrometry. This paper describes a method where two plant gums, arabic and tragacanth, were pyrolized in presence of silylating agents (HMDS e BSTFA alone and with TMCS as catalyst) using an on-line Py-GC/MS apparatus. Some characteristic trimethylsilyl derivatives of monosaccharides were identified on the basis of mass spectra. The presence of characteristic pyrolysis products of sugars allows to distinguish the two gums.

Determination of selected chlorohydrocarbons and polyaromatic hydrocarbons by gas chromatography–mass spectrometry in soils in Southwest Louisiana

The use of gas chromatography–mass spectrometry for the determination of selected polyaromatic hydrocarbons (PAHs) (anthracene and pyrene) and chlorohydrocarbons (hexachlorobutadiene and 1, 2, 4-trichlorobenzene) in soils from five areas in Southwest Louisiana was investigated. No detectable concentrations (below the detection limits) were found on or near the surface. However, trace levels of the PAHs were found at a depth in the 2 to 3 ft range below the surface levels.

Plant Volatiles Activating Specific Olfactory Receptor Neurons of the Cabbage Moth Mamestra brassicae L. (Lepidoptera, Noctuidae)

Herbivore insects are suitable model organisms for studying how plant odor information is encoded in olfactory receptor neurons (RNs). By the use of gas chromatography linked to electrophysiological recordings from single RNs, screening for sensitivity to naturally produced plant odorants is possible in order to determine the molecular receptive ranges of the neurons. Using this method, we have in this study of the cabbage moth, Mamestra brassicae, classified 21 types of olfactory RNs according to their responses to odorants present in the host plants of Brassicae, in the related species of Arabidopsis, as well as in essential oils of nonhost plants like ylang-ylang. Most of the RNs were tuned to one or a few structurally similar compounds, showing minimal overlap of their molecular receptive ranges. Whereas some RNs displayed a novel tuning, others were tuned to the same compounds as neurons in other insect species. We also found colocation in the same sensillum of 3 RN types with the same response characteristics and tuning as 3 colocated types described in heliothine moths living on different host plants. The presence of similar RN types across different insect species implies conservation or reappearance of the RN types, independent of the evolution of host plant ranges.

Focus on Alcohol & Drug Abuse: Ensuring Validity in Urine Drug Testing

Focus on Alcohol & Drug Abuse: Ensuring Validity in Urine Drug Testing

Focus on Alcohol & Drug Abuse: Ensuring Validity in Urine Drug Testing

Methods for urine drug testing have been available for several decades. These procedures are useful in assessing and identifying substance use in treatment programs, research programs, law enforcement, the workplace, and schools. Despite widespread adoption of such techniques, limited knowledge exists regarding their valid use and interpretation among many who frequently perform these tests. This column discusses how obtaining a valid test result is a complex process because results are affected by several factors, including the substance of interest, test methodology, pharmacokinetics, chain-of-custody procedures, and intentional tampering.

Prehistoric psychotropic consumption in Andean Chilean mummies

AbstractHallucinogenic plants are often regarded as the main source of psychoactive drugs in antiquity to reach deep altered states of consciousness^1,2^. Many researchers believe this was particularly true during the Tiwanaku empire expansion, circa (500-1000 A.D.), along the Atacama Desert of Chile. Highly decorated snuffing tablets and tubes are often found as grave goods during this period^3,4,5,6,7,8^. Until now the type of drugs consumed in this paraphernalia has been unclear. From the modern city of Arica, naturally mummified human bodies with abundant hair provided a unique opportunity to test for hallucinogenic plants consumed in Andean prehistory. Analysis by gas chromatography and mass spectrometry demonstrated the presence of harmine. The Banisteriopsis vine, commonly called Ayahuasca, was the probable source. This is the first confirmed evidence of psychoactive plant consumption in pre-Hispanic Andean populations along the Atacama coastal region. Of the 32 mummy hair samples analyzed 3 males tested positive for harmine. This alkaloid aids in the catalysis and synergic effects of powerful hallucinogenic drugs. The consumption of harmine was likely related to medicinal practices and not exclusively ingested by shamans. Another important aspect of this evidence is that Banisteriopsis is an Amazon plant. It does not grow in the Atacama coastal region. Thus, our findings reveal extensive plant trade networks in antiquity between the coast, desert, highlands, and Amazon basin. The excellent preservation of human organic specimens, the use of gas chromatography and mass spectrometry allowed us to map and demonstrate the consumption of psychoactive compound plants in Andean prehistory. In addition, our findings open the door for future studies to debate the consumption and social role of ancient psychoactive and hallucinogenic plants.

Study of Complex Reactions under Rapid Deactivation -- Improvements in the Reaction Equipment and in the Methodology for Kinetic Calculation

The technological development of catalytic processes under rapid deactivation requires the rigorous calculation of the deactivation kinetic equation in order to be useful in the simulation and optimization of industrial processes. Accordingly, suitable equipment for reaction and product analysis and a rigorous methodology for kinetic data analysis are required. These aspects are approached in this paper using the transformation of methanol into olefins on a SAPO-18 as the model reaction. In this reaction, deactivation is rapid and there is also an initiation period depending on process conditions. The correct use of gas chromatography allows for improving the collection of experimental data of composition with time-on-stream, given that, on the one hand, it minimizes the time required for analysis (4 min), and on the other, a better homogenization of the reaction product sample is achieved, which allows for a more accurate determination of the composition corresponding to a given time-on-stream. Furthermore, the rigorous kinetic modelling of deactivation requires a data analysis methodology that considers the past history of the catalyst and an activity to be defined based on a rigorous physical meaning. Accordingly, the concept of the integrated kinetic model has been used in this paper, whose basis is the calculation of kinetic parameters by simultaneously solving the zero time-on-stream kinetic model and the kinetic equation for deactivation.

Organochlorine pesticides in soils around Guanting Reservoir, China

Fifty-six representative samples of topsoil were collected around Guanting Reservoir, which is an important water source for Beijing. Concentrations of the insecticides HCH, DDT, and their metabolites were quantified by use of gas chromatography (GC) with electron capture detection (ECD). Organochlorine pesticides (OCPs) are still present in surface soils in the Guanting area. DDT accounts for about 93% of the total OCP content. Concentrations of alpha/gamma, beta/gamma, and DDT/DDE are the result not only of historical use, but also of more recent depositions. Statistical analyses, including principal component analysis (PCA) and cluster analysis (CA), revealed associations between concentrations of OCPs and major soil characteristics. Geographical information system (GIS) technology was used to develop maps of the distributions of OCP concentrations. The areas of greatest contamination were primarily in the central part of the study area and were correlated with greater population density, heavier traffic, and more industrial activity.

A Practical Guide to the Isolation, Analysis and Identification of Conjugated Linoleic Acid

Natural and synthetic conjugated linoleic acids (CLA) are reputed to have therapeutic properties that are specific to particular geometrical and positional isomers. Analysis of these has presented unique problems that have brought forward distinctive solutions, especially the use of gas chromatography-mass spectrometry and silver-ion high-performance liquid chromatography. In the analysis of CLA present at low levels in tissue samples, it is sometimes necessary to use concentration methods. In this review, the most useful and practical methods for the isolation and analysis of CLA isomers in tissues and in commercial CLA preparations are described.

Analysis of pesticide residues in fruit and vegetables with ethyl acetate extraction using gas and liquid chromatography with tandem mass spectrometric detection

A multiresidue method based on extraction with ethyl acetate has been used at the Swedish National Food Administration since 1989 to monitor pesticide residues in fruit and vegetables. The method has been continuously adjusted, resulting in simple and quick analyses of pesticide residues. To recover basic pesticides, the addition of an alkali is necessary. The addition of sodium hydrogen carbonate has been shown to recover all pesticides effectively without any degradation. The liquid chromatography (LC) with tandem mass spectrometry (MS/MS) technique has made it possible to analyse more polar pesticides and to replace many single methods. The latest development in the multiresidue method, comprising the use of gas chromatography (GC) with MS/MS, has further improved the analysis by replacing the conventional GC detectors. The need for cleanup has been reduced or eliminated entirely. Consequently, the method has been simplified in a way that makes it possible to recover all included analytes in many different matrices in one single extraction and to detect them either with GC-MS/MS or with LC-MS/MS.

Use of gas chromatography–mass spectrometry for identification of a new disaccharide in honey

Gas chromatography–mass spectrometry has been used to separate and identify disaccharides of edible honey. According to the characteristic fragmentation behaviour of disaccharide TMS-oximes, fructofuranosyl-(2-1)-fructose (inulobiose) has been structurally characterized. Identification was carried out on the basis of retention time on two columns of different polarity and mass spectrometric analysis. Inulobiose was found in honeys of different origins for the first time, varying within 0.93 and 6.14 mg/g of honey. Its occurrence in honeys is discussed.

Preparation and characterization of standard reference material 3276, carrot extract in oil

The National Institute of Standards and Technology (NIST), the Food and Drug Administration (FDA) Center for Drug Evaluation and Research (CDER) and Center for Food Safety and Applied Nutrition (CFSAN), and the National Institutes of Health (NIH), Office of Dietary Supplements (ODS) are collaborating to produce a series of standard reference materials (SRMs) for dietary supplements. Standard reference material (SRM) 3276 Carrot Extract in Oil is one in this series, with values assigned for trans-alpha-carotene, trans- and total beta-carotene, delta- and gamma-tocopherol, and twelve fatty acids. Results for carotenoids and tocopherols were obtained by use of combinations of liquid chromatography (LC), on columns of differing selectivity, with absorbance and mass spectrometric (MS) detection. Fluorescence detection also was used for the tocopherols. Results for fatty acids were obtained by use of gas chromatography (GC) with both flame-ionization and mass-spectrometric detection. This material is intended for use as a primary control material when assigning values to in-house (secondary) control materials and for validation of analytical methods for measurement of these analytes in similar matrices.

Urinary biomarkers to assess exposure of cats to environmental tobacco smoke

To evaluate the use of urinary biomarkers to assess exposure of cats to environmental tobacco smoke (ETS). 61 healthy client-owned cats (19 from households in which smoking was reported and 42 from households in which there was no smoking). Urine samples were obtained from each cat and assayed for total nicotine (nicotine plus nicotine glucuronide) and total cotinine (cotinine plus cotinine glucuronide) content by use of gas chromatography-mass spectrometry. In addition, total urinary content of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a major metabolite of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, was measured by use of gas chromatography with nitrosamine-selective detection. Cats from households in which smoking was reported had significantly higher concentrations of total nicotine (70.4 ng/mL), total cotinine (8.53 ng/mL), and total NNAL (0.0562 pmol/mL) in urine, compared with concentrations for cats that lived in households in which there was no smoking (4.89 ng/mL, 0.74 ng/mL, and 0.0182 pmol/mL, respectively). Analysis of these data provided biochemical evidence of exposure to ETS and uptake of tobacco-specific carcinogens by cats that live in households with smokers. Biomarkers could facilitate investigation of the health effects of ETS in cats and other species.

Use of gas chromatography–mass spectrometry combined with resolution methods to characterize the essential oil components of Iranian cumin and caraway

Gas chromatography–mass spectrometry combined with iterative and non-iterative resolution methods was used to characterize the essential oil components of Iranian cumin and caraway. Orthogonal projection resolution (OPR) as a non-iterative and distance-selection-multivariate curve resolution-alternative least squares (DS-MCR-ALS) as an iterative method were used as auxiliary means to the analysis in the case of overlapping peaks. A total of 19 and 39 components were identified by direct similarity searches for cumin and caraway oils, respectively. These numbers were extended to 49 and 98 components, respectively with the help of chemometric techniques. Major constituents in cumin are gamma-terpinene (15.82%), 2-methyl-3-phenyl-propanal (32.27%) and myrtenal (11.64%) and in caraway are gamma-terpinene (24.40%), 2-methyl-3-phenyl-propanal (13.20%) and 2, 4(10)-thujadien (14.02%). In spite of different cultivation conditions, there are 28 components which are common between the two seeds.

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Combined Lumbar-Plexus and Sciatic-Nerve Blocks: An Analysis of Plasma Ropivacaine Concentrations

Lumbar-plexus and sciatic-nerve blocks are commonly combined for lower-extremity anesthesia using large doses of ropivacaine. Limited information is available about the pharmacokinetics of this practice. We analyzed plasma ropivacaine concentrations after single-injection lumbar-plexus blocks with and without sciatic-nerve blocks. Twenty patients having lower-extremity surgery using a lumbar-plexus block with 0.5% ropivacaine with 1:400,000 epinephrine (35 mL, n = 10) or the same lumbar-plexus block with the addition of a sciatic-nerve block (25 mL, n = 10, 60 mL total) using the same solution were enrolled. Venous blood samples were collected at 5, 15, 30, 45, 60, 120, and 240 minutes after block placement and analyzed for total ropivacaine concentration by use of gas chromatography. Individual timepoints, maximum concentrations (C(max)), and time to C(max) (T(max)) were compared. Values are mean +/- SD. Both groups demonstrated a rapid increase in plasma concentration over the first 30 to 45 minutes. Concentrations were greater for those who received both blocks (P = .0005) at all timepoints. The lumbar-plexus block C(max) was less (986 +/- 221 ng/mL) than for the combined blocks (1,560 +/- 351 ng/mL, P = .0004). The T(max) was greater for the lumbar plexus (80 +/- 49 min) than for the combined blocks (38 +/- 22 min, P = .03). There was no relationship between the C(max) and patient age, weight, or body mass index. The results of this study demonstrate that the plasma ropivacaine concentrations increase quicker when a sciatic-nerve block is added to a lumbar-plexus block, but C(max) remains below the toxicity threshold.

Analysis of ethyl carbamate in Korean soy sauce using high-performance liquid chromatography with fluorescence detection or tandem mass spectrometry and gas chromatography with mass spectrometry

A specific, sensitive procedure involving high-performance liquid chromatography (HPLC) coupled to tandem mass spectrometry (MS/MS) was developed and compared to other analytical methods for quantification of ethyl carbamate (EC) in Korean soy sauce products. HPLC with a fluorescence detector was not applicable for monitoring trace amounts of EC in soy sauce due to its low detection limit (20 ppb). The use of gas chromatography (GC) coupled to MS could be applied to soy sauce, but it was not as simple and fast as HPLC/MS/MS. The GC/MS procedure exhibited excellent linearity over the concentration range of 10–200 ppb with a 0.5 ppb limit of detection (LOD) and 82.7 ± 3.1% recovery. A procedure involving HPLC/MS/MS with multiple reaction monitoring was developed. The characteristic transitions of m/ z 90 → 62 for EC as well as m/ z 104 → 62 for propyl carbamate (PC) as the internal standard were monitored. Good linearity was obtained both in the range from 10 to 100 ppb and in the range from 0.1 to 20 ppb with a LOD of 0.05 ppb. The average recovery was 92.2 ± 1.7%. The applicability of the GC/MS and developed HPLC/MS/MS methods was demonstrated by detection of EC in 12 kinds of commercial Korean soy sauce products at levels of 0.5 and 0.1 ppb, respectively. The new HPLC/MS/MS method provided greater sensitivity with a simpler and shorter confirmatory analysis than the GC/MS method.

Determination of epichlorohydrin in water and sewage samples

The simple, quick and effective methods for the analysis of epichlorohydrin (ECH) in water and sewage samples with the use of gas chromatography have been presented. From among all the methods developed, the procedures for monitoring drinking-water quality and the methods which allow the determination of epichlorohydrin in sewage samples have been selected. The limits of ECH detection have been determined by direct aqueous injection (DAI) into the chromatographic column and an analysis with the application of a flame ionization detector (FID), a mass spectrometry detector (MS), an electron capture detector (ECD) and atomic emission detection (AED) detectors. The method allows the determination of ECH in water samples at the concentration level of 0.1 mg l −1. Moreover, the developed methods of water samples preparation for chromatographic analysis using the following extraction methods: headspace (HS), stripping with adsorption on solid phase, liquid–liquid extraction (LLE), solid phase extraction (SPE) and solid phase microextraction (SPME) have been evaluated. The limits of ECH detection for each procedure with the application of gas chromatography (GC) combined with various detectors have been determined and their statistical evaluation has been presented. The SPME method allowed us to determine ECH in water samples at the concentration levels of 1.0 ng l −1. The results of studies on the choice of the selective methods allowing ECH analysis in sewage samples have been demonstrated. The applied SPME method was found to be a quick and effective technique to determine micro trace amounts of ECH in samples containing high amounts of various organic compounds.