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PubMed2003

GC-MS of ignitable liquids using solvent-desorbed SPME for automated analysis.

Solid-phase microextraction (SPME) is well documented with respect to its convenience and applicability to sampling volatiles. Nonetheless, fire debris analysts have yet to widely adopt SPME as a viable extraction technique, although several fire debris studies have demonstrated the utility of SPME coupled with gas chromatography-mass spectrometry (GC-MS) to identify ignitable liquids. This work considers the expansion of SPME sampling from the customary thermal desorption mode to solvent-based analyte desorption for the analysis of ignitable residues. SPME extraction fibers are desorbed in 30 microL of nonaqueous solvent to yield a solution amenable to conventional GC-MS analysis with standard autosampler apparatus. This approach retains the advantages of convenience and sampling time associated with thermal desorption while simultaneously improving the flexibility and throughput of the method. Based on sampling results for three ignitable liquids (gasoline, kerosene, anddiesel fuel) in direct comparisons with the widely used activated charcoal strip (ACS) method this methodology appears to be a viable alternative to the routinely used ACS method.

Journal Article↗
PubMed2006

Study of barrier properties and chemical resistance of recycled PET coated with amorphous carbon through a plasma enhanced chemical vapour deposition (PECVD) process.

Many studies have been carried out in order to make bottle-to-bottle recycling feasible. The problem is that residual contaminants in recycled plastic intended for food packaging could be a risk to public health. One option is to use a layer of virgin material, named functional barrier, which prevents the contaminants migration process. This paper shows the feasibility of using polyethylene terephthalate (PET) recycled for food packaging employing a functional barrier made from hydrogen amorphous carbon film deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) process. PET samples were deliberately contaminated with a series of surrogates using a FDA protocol. After that, PET samples were coated with approximately 600 and 1200 Angstrons thickness of amorphous carbon film. Then, the migration tests using as food simulants: water, 10% ethanol, 3% acetic acid, and isooctane were applied to the sample in order to check the chemical resistance of the new coated material. After the tests, the liquid extracts were analysed using a solid-phase microextraction device (SPME) coupled to GC-MS.

Carbon↗
PubMed1998

Characterization of metabolites in the biotransformation of 2,4,6-trinitrotoluene with anaerobic sludge: role of triaminotoluene.

The present study describes the biotransformation of 2,4,6-trinitrotoluene (TNT) (220 microM) by using anaerobic sludge (10%, vol/vol) supplemented with molasses (3.3 g/liter). Despite the disappearance of TNT in less than 15 h, roughly 0.1% of TNT was attributed to mineralization (14CO2). A combination of solid-phase microextraction-gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry identified two distinctive cycles in the degradation of TNT. One cycle was responsible for the stepwise reduction of TNT to eventually produce triaminotoluene (TAT) in relatively high yield (160 microM). The other cycle involved TAT and was responsible for the production of azo derivatives, e.g., 2,2',4,4'-tetraamino-6,6'-azotoluene (2,2',4, 4'-TA-6,6'-azoT) and 2,2',6,6'-tetraamino-4,4'-azotoluene (2,2',6, 6'-TA-4,4'-azoT) at pH 7.2. These azo compounds were also detected when TAT was treated with the anaerobic sludge but not with an autoclaved sludge, suggesting the biotic nature of their formation. When the anaerobic conditions in the TAT-containing culture medium were removed by aeration and/or acidification (pH 3), the corresponding phenolic compounds, e.g., hydroxy-diaminotoluenes and dihydroxy-aminotoluenes, were observed at room temperature. Trihydroxytoluene was detected only after heating TAT in water at 100 degrees C. When 13CH3-labeled TNT was used as the N source in the above microcosms, we were unable to detect 13C-labeled p-cresol or [13CH3]toluene, indicating the absence of denitration or deamination in the biodegradation process. The formation and disappearance of TAT were not accompanied by mineralization, suggesting that TAT acted as a dead-end metabolite.

Anaerobiosis↗
PubMed2002

Survey on the presence of butyltin compounds in chinese alcoholic beverages, determined by using headspace solid-phase microextraction coupled with gas chromatography-flame photometric detection.

The use of butyltin compounds in some food packaging leads to the contamination of liquid food and may result in subsequent adverse effects on people's health through the food chain. A survey of butyltin compounds in Chinese alcoholic beverages purchased from retail markets was carried out by using solid-phase microextraction (SPME) followed by gas chromatography coupled with flame photometric detection. Forty-four samples including wine, liquor, and champagne were studied. The levels of monobutyltin and dibutyltin ranged from <0.016 to 5.687 and from <0.0022 to 33.257 microg of Sn/L, respectively. Low levels of tributyltin were detected. The presence of dibutyltin in wine samples was further confirmed by GC-MS. The result indicated that dry wines generally contained more dibutyltin than sweet wines. The concentrations of butyltin compounds in liquor samples were lower than those in wine samples.

Alcoholic Beverages↗
PubMed2005

Study of both sunflower oil and its headspace throughout the oxidation process. Occurrence in the headspace of toxic oxygenated aldehydes.

The static headspace composition of sunflower oil throughout the oxidation process at 70 degrees C with circulating air is studied by means of solid-phase microextraction followed by gas chromatography-mass spectrometry (SPME-GC-MS); at the same time the liquid phase of the same oil is studied by means of Fourier transform infrared (FTIR) spectroscopy. Each technique provides complementary information about the process; FITR spectroscopy detects changes in the functional groups of the liquid matrix in a global way and SPME/GC-MS provides information about the different components present in the volatile phase during the oxidation process. Concordance between the timing of the changes produced in both liquid and gaseous phases is observed, as well as agreement and complementarity in the results obtained from both phases. The formation of some well-known genotoxic and cytotoxic oxygenated aldehydes in this process and their presence in the oil headspace are proved.

Aldehydes↗
PubMed2004

Identification of biogenic organotellurides in Escherichia coli K-12 headspace gases using solid-phase microextraction and gas chromatography.

Escherichia coli JM109 cells, expressing the genes encoded in a 3.8-kb chromosomal DNA fragment from Geobacillus stearothermophilus V, produced volatile organotellurium compounds which were released into the headspace gas above liquid cultures when amended with tellurite anions in micromolar amounts. Headspace sampling was achieved using gas-syringe extraction or solid-phase microextraction using carboxen-polydimethysiloxane fibers. In addition to dimethyl telluride and dimethyl ditelluride, two new organometalloidal compounds were detected using gas chromatograph with mass spectrometric or fluorine-induced chemiluminescence detection. These compounds are methanetellurol and dimethyl tellurenyl sulfide. The significance of these findings with regard to the current knowledge about bacterial tellurite resistance is discussed.

Adaptation, Biological↗
PubMed1999

Liquid-liquid-liquid microextraction for sample preparation of biological fluids prior to capillary electrophoresis.

Methamphetamine as a model compound was extracted from 2.5-mL aqueous samples adjusted to pH 13 (donor solution) through a thin phase of 1-octanol inside the pores of a polypropylene hollow fiber and finally into a 25-microL acidic acceptor solution inside the hollow fiber. Following this liquid-liquid-liquid microextraction (LLLME), the acceptor solutions were analyzed by capillary zone electrophoresis (CE). Extractions were performed in simple disposable devices each consisting of a conventional 4-mL sample vial, two needles for introduction and collection of the acceptor solution, and a 8-cm piece of a porous polypropylene hollow fiber. From 5 to 20 different samples were extracted in parallel for 45 min, providing a high sample capacity. Methamphetamine was preconcentrated by a factor of 75 from aqueous standard solutions, human urine, and human plasma utilizing 10(-1) M HCl as the acceptor phase and 10(-1) M NaOH in the donor solution. In addition to preconcentration, LLLME also served as a technique for sample cleanup since large molecules, acidic compounds, and neutral components were not extracted into the acceptor phase. Utilizing diphenhydramine hydrochloride as internal standard, repetitive extractions varied less than 5.2% RSD (n = 6), while the calibration curve for methamphetamine was linear within the range 20 ng/microL to 10 micrograms/mL (r = 0.9983). The detection limit of methamphetamine utilizing LLLME/CE was 5 ng/mL (S/N = 3) in both human urine and plasma.

Diphenhydramine↗
PubMed2001

Multiresidue determination of organophosphorus and organochlorine pesticides in human biological fluids by capillary gas chromatography.

Two multiresidue analytical methods for the simultaneous determination of organophosphorus and organochlorine pesticides in human urine and serum samples are described. The first approach is based on liquid-liquid microextraction with dichloromethane, and the second uses solid-phase extraction with C18. In both methods, the extracts are analyzed by capillary gas chromatography using nitrogen-phosphorus detection (NPD) and electron-capture detection (ECD). Limits of detection of the overall procedure of analysis are at the low ng mL(-1) level. Stability experiments have been performed with spiked urine and serum samples stored at 4 degrees C for 1 month. Finally, the solid-phase extraction procedure was applied to real-world samples. Quantification was performed by NPD or ECD, and peak identity was confirmed by use of mass-selective detection (MSD).

Chromatography, Gas↗
PubMed2005

Rapid absorption of dietary 1,8-cineole results in critical blood concentration of cineole and immediate cessation of eating in the common brushtail possum (Trichosurus vulpecula).

The blood concentration of 1,8-cineole and its metabolites was measured in six male brushtail possums while they voluntarily fed on diets laced with varying concentrations of cineole for 3 d. On the third day, blood samples were collected during and after each bout of feeding for 3 hr. Blood cineole was measured by using headspace solid-phase microextraction (SPME), while cineole metabolites were measured by liquid-liquid extraction followed by gas chromatography-mass spectroscopy. Feeding patterns were measured by continual recording of residual food weight and time. Cineole absorption was rapid, resulting in a peak blood concentration at the end of each feeding bout. The blood concentration of cineole did not exceed a critical value (51.8 +/- 14.1 micromol/l) regardless of the concentration in the diet. Food and, therefore, cineole intake was regulated. The amount of food ingested in the first feeding bout decreased from 236 +/- 52 g on the control diet to 36 +/- 20 g on the 4% cineole diet. The amount of cineole ingested in the first bout (1.18 +/- 1.10 g) was the same regardless of the dietary concentration and was controlled by the size of the meal. Total food eaten during the 7-hr feeding session decreased by 64% from 368 +/- 94 g (control diet) to 131 +/- 52 g (4% diet). Total cineole intake increased from 2.47 +/- 0.60 g (1% diet) to 5.05 +/- 2.41 g (4% diet). Cineole metabolites accumulated throughout the sampling period and were generally still rising at the end of blood sampling period. Blood levels of metabolites were at least 10-fold higher than cineole levels. The immediate control of feeding seems to be regulated by blood levels of cineole, whereas metabolites are likely to be more important in regulating the chronic ingestion of cineole.

Analysis of Variance↗
PubMed2000

Analysis of organic sulfur compounds in wine aroma.

Sulfur-containing compounds in wines have been extensively studied because of their effect on wine aroma. The aim of this paper was to give an overview on the analytical methods developed to determine them in wines with special emphasis on gas chromatographic methods, as well as the results obtained. In addition, the problems occurring in application of the common extraction procedures, such as liquid-liquid extraction, static and dynamic headspace and solid-phase microextraction, are presented and discussed.

Sulfur Compounds↗
PubMed2003

Physico-chemical approach to study organotin sorption-desorption during solid-phase microextraction.

Solid-phase microextraction (SPME) has become a real alternative to liquid-liquid extraction in the field of speciation of organometallic compounds. Despite the high performance of this preconcentration technique, matrix effects in natural samples can affect the analytical precision. In order to understand the origin of these disturbances and control the extraction step as best as possible, the sorption-desorption behaviour of organotins was studied. In the first part, this paper discusses the analytical problems encountered in the daily use of SPME due to the particular problems observed for phenyltins. The sorption profile of these compounds was modelled using experimental design methodology to confirm the first-order kinetics. Desorption of the compounds was also observed after a given time and could not be attributed to competition between organotin compounds. In the same way, butyl- and phenyltins were studied in the presence of humic substances, which acted as representatives of organic matter found in natural samples. These substances drastically decrease the extraction yields, but do not affect the sorption profile of butyl- and phenyltins.

Humic Substances↗
PubMed2001

[Advances in chromatography and related techniques in China--status report in 1998-1999].

This report covers developments in chromatography and related techniques in China during the period of 1998-1999. The papers published in 23 domestic and a few foreign periodicals which are closely related to chromatography, and presented at 1999 Beijing Conference and Exhibition on Instrumental Analysis and the 12th National Symposium of Chromatography are reviewed. Specific topic areas covered include gas chromatography (GC), high performance liquid chromatography (HPLC), capillary electrophoresis (CE) and capillary electrochromatography (CEC), solid phase extraction (SPE) and solid phase microextraction (SPME).

Animals↗
PubMed1999

Determination of homocysteine and its related compounds by solid-phase microextraction-gas chromatography-mass spectrometry.

The purpose of this study was to develop a simple and accurate analytical method to determine homocysteine (Hcy), cysteine (Cys), and methionine (Met) in aqueous samples. Until now, the most frequently used method for the assay of Hcy, Cys, and Met has been high-performance liquid chromatography with fluorescence detection after fluorescent tagging. The newly developed method involves the employment of the SPME (solid-phase microextraction) technique together with GC-MS. For application to a gas chromatographic system, alkyl formate derivatives were prepared in the form of N(O,S)-alkoxycarbonyl alkyl ester with the analytes in the aqueous samples. The optimum derivatizing regent for N(O,S)-alkoxycarbonyl alkyl ester was chosen by comparing the efficiency of the derivatized analytes in a GC through the SPME method and liquid-liquid extraction. The optimum conditions of the SPME system for the analytes derivatized with N(O,S)-ethoxycarbonyl propyl ester in the aqueous matrix were pH 3.0 and no salt, and 30 min equilibration time using an 85 microm PA (polyacrylate) fiber. The developed method is inexpensive, easy and rapid.

Calibration↗
PubMed2005

Application of solid-phase microextraction combined with derivatization to the enantiomeric determination of amphetamines.

The utility of combining chiral derivatization and solid-phase microextraction (SPME) for the enantiomeric analysis of primary amphetamines by liquid chromatography has been investigated. Different derivatization/extraction strategies have been evaluated and compared using the chiral reagent o-phthaldialdehyde (OPA)-N-acetyl-l-cysteine (NAC) and fibres with a Carbowax-templated resin coating. Amphetamine, norephedrine and 3,4-methylenedioxyamphetamine (MDA) were used as model compounds. On the basis of the results obtained, a new method is presented based on the derivatization of the analytes in solution followed by SPME of the OPA-NAC derivatives formed. The proposed conditions have been applied to determine the compounds of interest at low ppm levels (<or=10 microg/ml) in aqueous and urine samples. Data on the linearity, reproducibility, sensitivity and selectivity are given. The utility of the described procedure for the quantification of amphetamine, norephedrine and MDA enantiomers in different kind of samples is also discussed.

Amphetamines↗
PubMed1999

Solid-phase microextraction coupled with gas chromatography-ion trap mass spectrometry for the analysis of haloacetic acids in water.

Headspace solid-phase microextraction (SPME) was studied as a possible alternative to liquid-liquid extraction for the analysis of haloacetic acids (HAAs) in water. The method involves derivatization of the acids to their ethyl esters using sulphuric acid and ethanol after evaporation, followed by headspace SPME with a polydimethylsiloxane fibre and gas chromatography-ion trap mass spectrometry (GC-IT-MS). The derivatization procedure was optimized: maximum sensitivity was obtained with esterification for 10 min at 50 degrees C in 30 microl of sulphuric acid and 40 microl of ethanol. The headspace SPME conditions were also optimized and good sensitivity was obtained at a sampling temperature of 25 degrees C, an absorption time of 10 min, the addition of 0.1 g of anhydrous sodium sulfate and a desorption time of 2 min. Good precision (RSD lower than 10%) and detection limits in the ng l(-1) range (from 10 to 200 ng l(-1)) were obtained for all the compounds. The optimized procedure was applied to the analysis of HAAs in tap water and the results obtained by standard addition agreed with those of EPA method 552.2, whereas discrepancies due to matrix interferences were observed using external calibration. Consequently, headspace SPME-GC-IT-MS with standard addition is recommended for the analysis of these compounds in drinking water.

Acetates↗
PubMed2006

Development of a simple, accurate SPME-based method for assay of VOCs in column breakthrough experiments.

Solid-phase microextraction (SPME) with gas chromatography is to be used for assay of effluent liquid samples from soil column experiments associated with VOC fate/transport studies. One goal of the fate/transport studies is to develop accurate, highly reproducible column breakthrough curves for 1,2-cis-dichloroethylene (cis-DCE) and trichloroethylene (TCE) to better understand interactions with selected natural solid phases. For SPME, the influences of the sample equilibration time, extraction temperature and the ratio of volume of sample bottle to that of the liquid sample (V(T)/V(w)) are the critical factors that could influence accuracy and precision of the measured results. Equilibrium between the gas phase and liquid phase was attained after 200 min of equilibration time. The temperature must be carefully controlled due to variation of both the Henry's constant (K(h)) and the fibre/gas phase distribution coefficient (K(fg)). K(h) decreases with decreasing temperature while K(fg) increases. Low V(T)/V(w) yields better sensitivity but results in analyte losses and negative bias of the resultant assay. High V(T)/V(w) ratio yields reduced sensitivity but analyte losses were found to be minimal, leading to better accuracy and reproducibility. A fast SPME method was achieved, 5 min for SPME extraction and 3.10 min for GC analysis. A linear calibration function in the gas phase was developed to analyse the breakthrough curve data, linear between a range of 0.9-236 microgl(-1), and a detection limit lower than 5 microgl(-1).

Chromatography, Gas↗
PubMed1999

Identification and characterization of fenton oxidation products of surfactants by ionspray mass spectrometry and solid-phase microextraction gas chromatography mass spectrometry 1. Lauryl sulphate

The Fenton reaction for the degradation of surfactants has been investigated and partial degradation products have been identified and characterized by mass spectrometry for the case of lauryl sulphate. The polar soluble products were investigated by liquid chromatography/mass spectrometry (LC/MS) with electrospray ionization (ESI), and the volatile products leaving the mixture during the reaction were trapped by means of solid-phase microextraction (SPME) and investigated by gas chromatography/mass spectrometry (GC/MS) with electron and chemical ionization. The oxidation leads to the formation of products with hydroxyl and epoxide groups due to insertion of oxygen atoms or to aldehydes derived from the loss of the hydrophilic sulphate group. The extent of mineralization is dependent on peroxide and iron concentrations. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗
PubMed2004

Microextraction in packed syringe (MEPS) for liquid and gas chromatographic applications. Part II--Determination of ropivacaine and its metabolites in human plasma samples using MEPS with liquid chromatography/tandem mass spectrometry.

A new technique for sample preparation on-line with liquid chromatographic/tandem mass spectrometric (LC/MS/MS) assay was developed. Microextraction in a packed syringe (MEPS) is a new miniaturized, solid-phase extraction technique that can be connected on-line to gas or liquid chromatography without any modifications. In MEPS approximately 1 mg of the solid packing material is inserted into a syringe (100-250 microl) as a plug. Sample preparation takes place on the packed bed. The bed can be coated to provide selective and suitable sampling conditions. The new method is very promising, very easy to use, fully automated, of low cost and rapid in comparison with previously used methods. This paper presents the development and validation of a method for MEPS on-line with LC/MS/MS. Ropivacaine and its metabolites (PPX and 3-OH-ropivacaine) in human plasma samples were used as model substances. The method was validated and the calibration curves were evaluated by means of quadratic regression and weighted by the inverse of the concentration, 1/x, for the calibration range 2-2000 nM. The applied polymer could be used more than 100 times before the syringe was discarded. The extraction recovery was between 40 and 60%. The results showed high correlation coefficients (R(2) > 0.999) for all analytes in the calibration range studied. The accuracy, expressed as a percentage variation from the nominal concentration values, ranged from 0 to 6%. The precision, expressed as the relative standard deviation, at three different concentrations (quality control samples) was consistently about 2-10%. The limit of quantification was 2 nM.

Blood Chemical Analysis↗