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PubMed2004

Determination of fuel dialkyl ethers and BTEX in water using headspace solid-phase microextraction and gas chromatography-flame ionization detection.

A simple procedure for the determination of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), ethyl butyl ether (EBE), tert-amyl methyl ether (TAME), benzene, toluene, ethylbenzene, and xylenes (BTEX) in water using headspace (HS) solid-phase microextraction (HS-SPME) was developed. The analysis was carried out by gas chromatography (GC) equipped with flame ionization detector (FID) and 100% dimethylpolysiloxane fused capillary column. A 2 Plackett-Burman design for screening and a central composite design (CCD) for optimizing the significant variables were applied. Fiber type, extraction temperature, sodium chloride concentration, and headspace volume were the significant variables. A 65 microm poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) SPME fiber, 10 degrees C, 300 g/l, and 20 ml of headspace (in 40 ml vial) were respectively chosen for the best extraction response. An extraction time of 10 min was enough to extract the ethers and BTEX. The relative standard deviation (R.S.D.) for the procedure varied from 2.6 (benzene) to 8.5% (ethylbenzene). The method detection limits (MDLs) found were from 0.02 (toluene, ethylbenzene, and xylenes) to 1.1 microg/l (MTBE). The optimized method was applied to the analysis of the rivers, marinas and fishing harbors surface waters from Gipuzkoa (North Spain). Three sampling were done in 1 year from June 2002 to June 2003. Toluene was the most detected analyte (in 90% of the samples analyzed), with an average concentration of 0.56 microg/l. MTBE was the only dialkyl ether detected (in 15% of the samples) showing two high levels over 400 microg/l that were related to accidental fuel spill.

Chromatography, Gas↗

PubMed2006

Evaluation of a valveless thermal desorption system for organic aerosols and vapors. Transfer lines and preconcentration module.

Semivolatile organic compounds (SVOCs) are distributed in the atmosphere between the gas- and aerosol-phases. The low vapor pressures of some SVOCs makes thermal extraction and transfer through gas chromatographic (GC) systems difficult. We evaluated a programmable temperature vaporization (PTV) GC inlet, which served as the preconcentration module, and four open-tubular capillaries (Silcosteel- and Siltek-treated stainless steel, Silcosteel-treated stainless steel coated with 100% dimethylpolysiloxane, and deactivated fused silica) as transfer lines in a valveless, whole-sample analytic system. Thermal extraction of C(9)-C(36)n-alkanes at 300 and 320 degrees C from fused silica and quartz wool in the PTV inlet was equally efficient. Adsorptive losses of C(22)-C(36)n-alkanes to stainless steel surfaces that protruded into the PTV inlet were suspected. Thus, treatment of the outer surfaces of transfer lines is recommended for effective thermal transfer of SVOCs. Transfer efficiencies began to decline after n-C(24), n-C(28), and n-C(30) in Silcosteel-treated stainless steel, deactivated fused silica, and Siltek-treated stainless steel transfer lines, respectively. Thus, quantitative recovery at 320 degrees C of compounds with vapor pressures less than about 3 x 10(-8)Pa is not expected in valveless SVOC thermal desorption systems that use Siltek-treated stainless steel transfer lines and fused silica or quartz wool as preconcentration substrates.

Aerosols↗

PubMed2006

In-tube solid-phase microextraction-capillary liquid chromatography as a solution for the screening analysis of organophosphorus pesticides in untreated environmental water samples.

This paper describes a method for the selective screening of organophosphorus pesticides in water. In-tube solid-phase microextraction (SPME) in an open capillary column coupled to capillary liquid chromatography (LC) with UV detection has been used to effect preconcentration, separation and detection of the analytes in the same assembly. For in-tube SPME two capillary columns of the same length and different internal diameters and coating thicknesses have been tested and compared, a 30 cm x 0.25 mm I.D., 0.25 micro m thickness coating column, and a 30 cm x 0.1 mm I.D., 0.1 micro m of coating thickness column. In both columns the coating was 95% dimethylpolysiloxane (PDMS)-5% diphenylpolysiloxane. The proposed methodology provided limits of detections (LODs) for the tested organophosphorus pesticides in the 0.1-10 micro g/L range, whereas the direct injection of the samples onto the capillary LC system provided LODs in the 50-1000 micro g/L range. The sensitivity of the proposed in-tube SPME-capillary LC method is adequate to monitorize the analyte levels in drinking water. Several triazines, polycyclic aromatic hydrocarbons (PAHs), nonylphenol, organochloride pesticides or polybrominated diphenyl ethers (PBDEs) have been evaluated as possible interferents. The reliability of the described method is demonstrated by analysing different real water samples.

Chromatography, Liquid↗

PubMed2004

Development of a gas chromatographic test for the quantification of the biomarker 3-bromopropionic acid in human urine.

An accurate and precise method was developed for the detection and quantification of 3-bromopropionic acid (3-BPA), a metabolite and biomarker for exposure to 1-bromopropane (1-BP). 1-BP is used as an industrial solvent and exposure is a health concern for industrial workers due to its toxicity. It has been associated with neurological disorders in both animals and humans. Urine sample preparation for the determination of 3-BPA consisted of liquid-liquid extraction (LLE) with ethyl acetate and silylation with N-methyl-N-[tert-butyldimethylsilyl]trifluoroacetamide (MTBSTFA). Quantification was by means of a gas chromatograph (GC) equipped with a mass selective detector (MSD) using a dimethylpolysiloxane (HP-1) capillary column and 3-chloropropionic acid was used as an internal standard in the procedure. Demonstrated accuracy and precision during this method's validation was good; recovery varied between 93 and 98% with relative standard deviations (R.D.S.) of 5.7% or less. The limit of detection (LOD) for the procedure was approximately 0.01microg/ml 3-BPA in urine. These data and other factors of the development and validation of this test method will be discussed.

Biomarkers↗

PubMed2004

Determination of a cyclooxygenase II inhibitor in human plasma by capillary gas chromatography with mass spectrometric detection.

Sensitive methods based on capillary gas chromatography (GC) with mass spectrometric (MS) detection in a selected-ion monitoring mode (SIM) for the determination of a cyclooxygenase II (COX-II) inhibitor (3-isopropoxy-4-(4-methanesulfonylphenyl)-5,5'-dimethyl-5H-furan-2-one, I) in human plasma, in two concentration ranges of 0.1-20 and 5-1000 ng/ml, are described. Following liquid-liquid extraction, the residue, after evaporation of the organic phase to dryness, was reconstituted in acetonitrile (20 l) and part of the extract (1 l) was analyzed by GC/MS/SIM. The drug (I) and internal standard (II) were separated on a 25 mx0.2 mm capillary column with HP Ultra 1 (100% dimethylpolysiloxane, 0.33 m) phase and analyzed by MS/SIM monitoring ions at m/z 237 and 282 for I and II, respectively. The standard curve was linear within the lower concentration range of 0.1-20 ng/ml and the lower limit of quantification (LLOQ) in plasma was 0.1 ng/ml. Intraday coefficients of variation (CV, n=5) were 8.9, 4.2, 5.7, 3.1, 1.9, 1.9, and 4.4% at 0.1, 0.2, 0.5, 1.0, 5.0, 10, and 20 ng/ml, respectively. The standard curve was also linear within the higher concentration range of 5-1000 ng/ml and the LLOQ in plasma was 5 ng/ml. Intraday coefficients of variation (CV, n=5) were all below 9% at all concentrations within the standard curve range. The accuracy for I in human plasma was 91-112% and the recovery of I and II was greater than 70% at all concentrations within both standard curve ranges. The details of the assay methodology are presented.

Cyclooxygenase Inhibitors↗

PubMed2005

Development of a headspace gas chromatographic test for the quantification of 1- and 2-bromopropane in human urine.

A test procedure was developed for the detection and quantification of 1- and 2-bromopropane in human urine. 1-Bromopropane (1-BP) is a commonly used industrial solvent, and 2-bromopropane (2-BP) is often found as an impurity component in industrial grade 1-BP. Both compounds are a health concern for exposed workers due to their chronic toxicity. Bromopropanes have been associated with neurological disorders in both animals and humans. Sample preparation consisted of diluting urine with water and fortification with 1-bromobutane (1-BB), which was used as an internal standard; then each sample was sealed in a headspace vial. A static-headspace sampler (Teledyne-Tekmar Model 7000) was used to heat each sample at 75 degrees C for a 35-min equilibrium time. Quantification was by means of a gas chromatograph (GC) equipped with an electron capture detector (ECD) and a dimethylpolysiloxane (DB-1) capillary column. A recovery study using fortified urine samples at multiple concentrations (0.5-8 microg/ml) demonstrated full recovery; 104-121% recovery was obtained. Precision ranged from 5 to 17% for the 15-20 spiked samples used at each concentration, which were analyzed over multiple experimental trial days. The limit of detection (LOD) for this test procedure was approximately 2 ng/ml 1-BP and 7 ng/ml 2-BP in urine. A recovery study of 1- and 2-BP from fortified urine stored in vials appropriate for field collection was also completed. These results and other factors of the development and validation of this test procedure will be discussed.

Chromatography, Gas↗

PubMed2006

Rapid, accurate, and sensitive fatty acid ethyl ester determination by gas chromatography-mass spectrometry.

BACKGROUND: Fatty acid ethyl esters (FAEEs) are useful markers of ongoing alcohol use and may be associated with alcohol-induced damage to the liver and pancreas. In this article, we describe a novel method for rapid determination of the three major FAEEs found in human plasma. METHODS: Internal standard, ethyl heptadecanoate, was added to plasma samples, and FAEEs were isolated by acetone precipitation, hexane lipid extraction, and amino-propyl silica solid phase extraction. FAEEs were quantitated by gas chromatography-mass spectrometry (GC-MS) using a nonpolar dimethylpolysiloxane column. The accuracy, precision, specificity, and sensitivity of the assay were defined from plasma samples from recently drinking and abstinent persons, with and without the addition of FAEEs. RESULTS: Individual FAEE peaks demonstrated excellent resolution. Instrument time was reduced by more than 60%. The lower limit of detection was 5 to 10 nM, and the lower limit of quantitation for each FAEE was 60 nM (for 22 samples with known concentration 60 nM, x +/-SD: 61 +/- 5.7, 57 +/- 5.7, and 57 +/- 5.9 nM, for ethyl palmitate, ethyl oleate, and ethyl stearate, respectively). Instrument precision (coefficient of variance, CV) for these three FAEEs was 0.3%, 0.4%, and 0.7%, respectively. Intra-assay precision (CV) for total FAEEs was less than 7%. FAEEs were absent in 49 samples from abstinent persons. FAEEs were detected in all 76 samples with associated positive blood alcohol levels. CONCLUSIONS: Our method of FAEE analysis is rapid and potentially useful in research and clinical studies. FAEE determination using this method is precise, accurate, sensitive, and specific and deserves broader application.

Calibration↗

PubMed1999

Gas chromatography for in situ analysis of a cometary nucleus: characterization and optimization of diphenyl/dimethylpolysiloxane stationary phases.

The development of a gas chromatograph for the cometary sampling and composition (COSAC) experiment is described in the context of the preparation for the European Space Agency (ESA) Mission Rosetta for investigation of a cometary nucleus. COSAC is one out of ten experiments on the Rosetta Lander. Its scientific goal is to analyze in situ the chemical composition of the volatile constituents of the nucleus of the target comet P/Wirtanen. Constituted of several (up to eight) capillary wall-coated and porous-layer open tubular columns operating in parallel, the GC system is designed to separate and identify both organic and inorganic compounds which evolve from the comet naturally or are obtained from cometary samples through stepwise heating in a miniaturized pyrolizer. In this first part of our study, dimethylpolysiloxane (DMPS) stationary phases with increasing percentages of diphenyl substituted group (DP) have been investigated. A coupled experimental and theoretical approach has been taken in order to predict chromatographic data. By the use of a four-point experimental calibration (0 to 65% diphenyl group) in conjunction with Pro ezGC modeling software, results in prediction of multicomponent chromatograms with a mean error less than 5% for each compound retention time were obtained, irrespective of the stationary phase's diphenyl content and column physical parameters. The possibility to associate such phases is illustrated by the evolution of coelutions obtained on a non-polar (100% DMPS) and a medium polar (65% DP-DMPS) stationary phase, respectively. This study showed that with a small number of well tuned DP-DMPS columns, the separation and identification of most of the targeted compounds can be achieved with a minimum amount of coelutions and within the experiment requirements.

Alcohols↗

PubMed1982

Microemboli observed in deaths following cardiopulmonary bypass surgery: silicone antifoam agents and polyvinyl chloride tubing as sources of emboli.

Refractile foreign particles within clear vacuoles were observed in capillaries of 17 patients who underwent cardiopulmonary bypass surgery, died, and were autopsied at the George Washington University Hospital from December 1978 through April 1981. The postoperative survival time ranged from less than one day to more than eight months. The approximate maximal diameter of the individual particles was 10 micrometer and that of the vacuoles 60 micrometer. The particle-droplet complexes showed affinity for hydrophobic stains. In all 17 cases, the kidneys were involved in combination with several other organs. In two patients, the emboli were associated with microinfarcts in one or more organs. Scanning electron microscopy (SEM) of the polyvinyl chloride tubing used during four cardiopulmonary bypasses showed spallation and shredding of the luminal surface in the areas exposed to the roller pump heads. This suggested that fragments of polyvinyl chloride might be the particles in the emboli. Another possible source was the antifoam agent used in the bubble oxygenator. Scanning electron microscopy x-ray microprobe analysis of the foreign material within capillaries of several organs showed it to be strongly positive for silicon but not for chlorine. Therefore, it was concluded that the microemboli were droplets of antifoam agent, the refractile particles corresponding to the particulate silica component and the vacuoles corresponding to the dimethylpolysiloxane liquid component. Since x-ray microprobe analysis of the microemboli did not reveal a strong chloride peak, there is as yet no evidence that polyvinyl chloride fragments were involved in the microembolism. The morphologic findings reported here indicate that antifoam microembolization continues to complicate cardiopulmonary bypass surgery and must, therefore, be considered a potential cause of postoperative morbidity. The consequence of the fragments of polyvinyl chloride tubing released into the circulation remains to be established.

Antifoaming Agents↗

PubMed2000

Determination of clemastine in human plasma by gas chromatography with nitrogen-phosphorus detection.

A method for the quantitative determination of clemastine in human plasma has been developed and validated. The assay uses gas chromatography with nitrogen-phosphorus detection and a HP-1 capillary column (25 mx0.22 mm, film thickness 0.33 mm) coated with dimethylpolysiloxane. Clemastine (with orphenadrine as internal standard) was isolated from human plasma using liquid-liquid extraction. A linear relationship was observed between 0.1 and 12.8 ng/ml using the peak area ratio of clemastine to orphenadrine with a correlation coefficient greater than 0.99 (the detection limit for clemastine was 0.06 ng/ml). The intra- and inter-day coefficients of variation were less than 11%. The developed method was used for the analysis of plasma samples from healthy volunteers (n = 19) to examine the pharmacokinetics of the antihistamine clemastine after single and multiple oral doses of clemastine fumarate.

Adult↗

PubMed1997

Investigation of the triacylglycerol composition of iceman's mummified tissue by high-temperature gas chromatography.

The pattern of intact triacylglycerols of a skin sample from the 5300-year-old Iceman mummy (nicknamed Otzi) was resolved on a diphenyl-dimethylpolysiloxane stationary phase by high-temperature gas chromatography. Adipocere from a 64-year-old glacier mummy as well as recent human subcutaneous fat served as a comparison in this study. Qualitatively, the results for mummy samples were similar with well-preserved saturated, but decomposed unsaturated, triacylglycerols, the latter being predominant in subcutaneous fat. Excellent preservation of triacylglycerols with odd carbon numbers and branched acyl chains was observed. The results presented here shed new light on the process of mummification.

Adipose Tissue↗

PubMed2003

Novel approach for the analysis of glycated hemoglobin using capillary isoelectric focusing with chemical mobilization.

In this work, a novel CIEF methodology for the analysis of the glycated hemoglobin, HbA(1c), in dimethylpolysiloxane coated fused-silica capillaries (DB-1, 50 microm I.D., 27 cm, 0.20 microm coating thickness), using a narrow pH ampholyte mixture (4% pH 6-8:pH 3-10, 10:1, v/v) in 0.30% methylcellulose, was developed. In the focusing procedure, a 0.100-mol l(-1) phosphoric acid solution was used as anolyte and a 0.040-mol l(-1) NaOH solution was used as catholyte. During method development, two types of mobilization of the focused hemoglobins were tested: pressure and chemical mobilization. Chemical mobilization performed better, allowing the complete baseline resolution of the hemoglobin of interest, HbA(1c), from its adjacent peak, HbA, in less than 8 min. In the chemical mobilization procedure, the catholyte was replaced by a 0.040-mol l(-1) NaOH solution containing 0.080 mol l(-1) NaCl. The proposed methodology was applied to the analysis of 31 hemolysate samples and validated with respect to the selectivity, inter-assay and intra-assay precision (both migration time and hemoglobin percentage concentration). In addition, HbA(1c) determinations were compared for the CIEF method and a chromatographic standardized procedure using cation-exchanger columns (Variant, Bio-Rad), adopted in a local clinical laboratory, showing excellent correlation (r(2)=0.872, n=31). The slope was found to be statistically equal to one but the intercept differed from zero. Also the Bland-Altman plot indicates bias, implying that the CIEF method yields HbA(1c) concentration higher than the reference method. The separation of the hemoglobins HbA, HbA(2), HbF and HbA(1c) and the variants HbS and HbC was also demonstrated (8 min run). The resolving power of the proposed CIEF method allowed baseline resolution of hemoglobins with a pI difference as small as ca. 0.03, as it is the case for the pairs HbC/HbA(2) and HbA/HbA(1c).

Calibration↗

PubMed1998

Closure of the nasal vestibule in atrophic rhinitis--a new non-surgical technique.

A new technique is described for closing the nasal vestibule in cases of secondarily-acquired atrophic rhinitis. This involves occlusion of the nasal vestibule with an obturator made from dimethylpolysiloxane. Being a non-invasive method it is specifically indicated in the management of cases of secondarily-acquired atrophic rhinitis where any surgical treatment is contra-indicated. We describe its use in a case each of unilateral and bilateral secondary atrophic rhinitis.

Adult↗

PubMed2001

Capillary electrophoresis of sialic acid-containing glycoprotein. Effect of the heterogeneity of carbohydrate chains on glycoform separation using an alpha1-acid glycoprotein as a model.

alpha1-Acid glycoprotein (AGP) showed multiple peaks on separation using capillary electrophoresis in a chemically modified capillary with dimethylpolysiloxane at slightly acidic conditions. We analyzed glycoforms of AGP species after separation by ion-exchange chromatography, Con A affinity chromatography, and Cu(II)-chelating affinity chromatography. The AGP species thus obtained were digested with N-glycosidase F, and the released carbohydrate chains were analyzed by high-performance liquid chromatography after labeling with 3-aminobenzoic acid. The results afforded basic information on the contribution of carbohydrate chains to the separation mechanism of glycoforms of AGP by capillary electrophoresis. In addition, we describe an easy method for AGP analysis in serum samples using the electrokinetic injection.

Carbohydrate Sequence↗

PubMed2005

Electrically heated, air-cooled thermal modulator and at-column heating for comprehensive two-dimensional gas chromatography.

An instrument for comprehensive two-dimensional gas chromatography (GCxGC) is described using an electrically heated and air-cooled thermal modulator requiring no cryogenic materials or compressed gas for modulator operation. In addition, at-column heating is used to eliminate the need for a convection oven and to greatly reduce the power requirements for column heating. The single-stage modulator is heated by current pulses from a dc power supply and cooled by a conventional two-stage refrigeration unit. The refrigeration unit, together with a heat exchanger and a recirculating pump, cools the modulator to about -30 degrees C. The modulator tube is silica-lined stainless steel with an internal film of dimethylpolysiloxane. The modulator tube is 0.18 mm i.d. x 8 cm in length. The modulator produces an injection plug width as small as 15 ms.

Journal Article↗

PubMed2006

Generating multiple independent retention index data in dual-secondary column comprehensive two-dimensional gas chromatography.

A method producing simultaneously three retention indexes for compounds has been developed for comprehensive two-dimensional gas chromatography by using a dual secondary column approach (GC x 2GC). For this purpose, the primary flow of the first dimension column was equally diverted into two secondary microbore columns of identical geometry by means of a three-way flow splitter positioned after the longitudinally modulated cryogenic system. This configuration produced a pair of comprehensive two-dimensional chromatograms and generated retention data on three different stationary phases in a single run. First dimension retention indexes were determined on a polar SolGel-Wax column under linear programmed-temperature conditions according to the van den Dool approach using primary alcohol homologues as the reference scale. Calculation of pseudoisothermal retention indexes in both second dimensions was performed on low-polarity 5% phenyl equivalent polysilphenylene/siloxane (BPX5) and 14% cyanopropylphenyl/86% dimethylpolysiloxane (BP10) columns. To construct a retention correlation map in the second dimension separation space upon which KovAts indexes can be derived, two methods exploiting "isovolatility" relationships of alkanes were developed. The first involved 15 sequential headspace samplings of selected n-alkanes by solid-phase microextraction (SPME), with each sampling followed by their injection into the GC at predetermined times during the chromatographic run. The second method extended the second dimension retention map and consisted of repetitive introduction of SPME-sampled alkane mixtures at various isothermal conditions incremented over the temperature program range. Calculated second dimension retention indexes were compared with experimental values obtained in conventional one-dimensional GC. A case study mixture including 24 suspected allergens (i.e., fragrance ingredients) was used to demonstrate the feasibility and potential of retention index information in comprehensive 2D-GC.

Journal Article↗

PubMed1999

Development of a solid-phase microextraction GC-NPD procedure for the determination of free volatile amines in wastewater and sewage-polluted waters.

An analytical procedure for the determination of free volatile C1-C6 amines in aqueous matrixes has been developed and applied to their determination in waste-water, primary and secondary effluents, and sewage-polluted river samples. The developed analytical procedure involves headspace sampling using solid-phase microextraction with a poly(dimethylpolysiloxane) coating (100 microns) followed by GC-NPD determination and GC/MS confirmation using a tailor-made PoraPLOT amines capillary GC column for volatile amines. Procedural detection limits were compound dependent but ranged from 3 to 56 micrograms L-1, being close to or lower than the odor threshold concentration, and the reproducibility was ca. 15% (N = 5) in real water samples. The developed analytical procedure is solvent free, cost-effective (no cryogenic trap needed), and faster than existing methods because no derivatization step is involved in the determination. Linearity was compound dependent but ranged at least from 50 to 600 micrograms L-1.

Amines↗

PubMed1999

Column performance and stability for high-speed vacuum-outlet GC of volatile organic compounds using atmospheric pressure air as carrier gas.

The development of lightweight, portable GC instrumentation is handicapped by the need for compressed carrier gas to drive the separation. The use of air as carrier gas eliminates the need for compressed gas tanks. If a vacuum pump is used to pull carrier gas and injected samples through the column, atmospheric pressure air can be used as carrier gas. Vacuum outlet operation also improves performance for high-speed separations by reducing detector dead time and by shifting optimal carrier gas velocity to higher values. Under vacuum outlet conditions using atmospheric pressure air as carrier gas, a 6-m-long, 0.25-mm-i.d. capillary column can generate approximately 12,500 theoretical plates, and a 12-m-long column can generate approximately 44,000 plates but with a 3-4-fold increase in separation time. The principal issues in column selection for high-speed GC with air as a carrier gas are efficiency and stability. Several bonded and nonbonded stationary phases were evaluated for use with air as carrier gas in the analysis of volatile organic compounds of interest in airmonitoring applications. These include dimethylpolysiloxane, 50% phenyl-50% methyl polysiloxane, 50% cycanopropylphenyl-50% methyl polysiloxane, trifluoropropyl polysiloxane, poly(ethylene glycol), and dicyanoallyl polysiloxane (nonbonded). The dimethyl polysiloxane and the trifluoropropyl polysiloxane columns showed good efficiency and no significant deterioration after 5 days of continuous operation with air as carrier gas. The 50% phenyl-50% methyl polysiloxane and the 50% cycanopropylphenyl-50% methyl polysiloxane columns showed poorer efficiency, and the poly(ethylene glycol) and dicyanoallyl polysiloxane columns showed excessive deterioration in air.

Air↗