Determination of mono-alcohols by gas chromatography

A gas chromatographic method is described for the determination of alcohols up to C₂₀H₄₁OH. The procedure is rapid and indicates the molecular weight distribution and the contents of straight-chain and branched-chain alcohols. A programmed temperature control with a silicone substrate was satisfactory. n-C₁₄H₂₀OH and n-C₅H₁₁OH were used as internal standards.     

Determination of halogenated hydrocarbons by combined use of neutron activation analysis and capillary gas chromatography with electron-capture detection

Results obtained by the two techniques are compared. Two standard mixtures, one containing, HCB, DDT, DDE and DDD and the other chloro-, dichloro- and bromocyme, were at a halogen concentration of about 20, 2 and 0.2 mg l^?1. The neutron activation method gave an average recovery of 4% (relative standard deviation, 12%) based on 24 measurements for chlorine. For bromine, the figures were 99% and 11%, respectively. Volatile chlorinated organics pose a particular problem because they may evaporate during analysis. Investigations with chloroform as model substance, indicate that when sealed ampoules are used, the average recovery is 84% (r.s.d., 6%).     

Determination of busulfan in human plasma by gas chromatography with electron-capture detection

A simple and highly sensitive gas chromatographic method has been developed for the determination of busulfan in human plasma. After extraction of plasma specimens (clinical or spiked) with ethyl acetate, busulfan and the internal standard [1,8-bis(methanesulfonyloxy)octane] were derivatized with 2,3,5,6-tetrafluorothiophenol to yield compounds monitored by a 63Ni electron-capture detector. Sample recoveries from extraction and derivatization were greater than 78 and 91%, respectively. The limit of quantitation was 0.01 microgram/ml (0.04 microM) in 1 ml of plasma with a linear relationship over the 0.01-1.0 micrograms/ml (0.04-4 microM) concentration range. The method has been applied to analyze the plasma versus time profile of busulfan in human subjects following administration of an oral dose of 4 mg/kg per day as a marrow ablative chemotherapy for bone marrow transplantation.     

Determination of pesticide residues in lettuce by gas chromatography with electron-capture detection

A sensitive, rapid, and simple multiresidue method for the simultaneous determination of 19 pesticides in different varieties of lettuce (Lactuca sativum) was developed. Lettuce samples were extracted by homogenization with acetone and partitioned into ethyl acetate-cyclohexane. Subsequent sample cleanup was not needed. Final determination was made by capillary gas chromatography (GC) with electron-capture detection (ECD). Confirmation analysis of pesticides was performed by GC coupled with mass spectrometry in the selected ion monitoring mode. The average recovery by the GC-ECD method obtained for these compounds varied from 66.4 to 119.2% with relative standard deviations < 7.7%. The GC-ECD method has good linearity, and the detection limit for the pesticides studied varied from 0.1 to 3.8 microg/kg. The proposed method was used to determine pesticide levels in different types of lettuce grown in soils from experimental fields.     

Determination of fluvalinate residues in beeswax by gas chromatography with electron-capture detection

A simple, rapid, and accurate method is described for the determination of residual fluvalinate in beeswax. The procedure consists of partitioning on a disposable column of diatomaceous earth (Extrelut), followed by chromatographic cleanup on a Florisil cartridge. The final extract is analyzed by capillary gas chromatography with electron-capture detection (GC-ECD). Briefly, wax samples were dissolved in n-hexane, and the solutions were sonicated and transferred to Extrelut columns. The fluvalinate was extracted with acetonitrile, and a portion of the extract was cleaned up on a Florisil cartridge. The fluvalinate was eluted with diethyl ether-n-hexane (1 + 1) and directly determined by GC-ECD. Recoveries from wax samples spiked at 5 fortification levels (100-1500 microg/kg) ranged from 77.4 to 87.3%, with coefficients of variation of 5.12-8.31%. The overall recovery of the method was 81.4 +/- 3.2%, and the limit of determination was 100 microg/kg.     

Determination of toxaphene enantiomers by comprehensive two-dimensional gas chromatography with electron-capture detection

Comprehensive two-dimensional gas chromatography with micro electron-capture detection (GC x GC-microECD) has been evaluated for the enantioseparation of five chiral toxaphenes typically found in real-life samples (Parlar 26, 32, 40, 44 and 50). From the two enantioselective beta-cyclodextrin-based columns evaluated as first dimension column, BGB-176SE and BGB-172, the latter provided the best results and was further combined with three non-enantioselective columns in the second dimension: HT-8, BPX-50 and Supelcowax-10. The combination BGB-172 x BPX-50 was finally selected because it provided a complete separation among all enantiomers. A satisfactory repeatability and reproducibility of the retention times in both the first and the second dimension were observed for all target compounds (RSDs below 0.8%, n = 4). Linear responses in the tested range of 10-200 pg/microl and limits of detection in the range of 2-6 pg/microl were obtained. The repeatability and reproducibility at a concentration of 100 pg/microl, evaluated as the RSDs calculated for the enantiomeric fraction (EF), was better than 11% (n = 4) in all instances. The feasibility of the method developed for real-life analyses was illustrated by the determination of the enantiomeric ratios and concentration levels of the test compounds in four commercial fish oil samples. These results were compared to those obtained by heart-cut multidimensional gas chromatography using the same enantioselective column.     

Determination of ultramicro amounts of selenium by gas chromatography with electron-capture detection

Formation of piazselenols by the reaction of Se(IV) with 1,2-diaminobenzene and its derivatives, followed by solvent extraction and gas chromatography with electron-capture detection, provides the most sensitive means of determining selenium. By suitable chemical manipulation, the method can be used for Se(-II), Se(O), Se(IV) and Se(VI). Applications to a wide variety of samples are reviewed.     

Determination of organophosphorous pesticides in water using in-syringe ultrasound-assisted emulsification and gas chromatography with electron-capture detection

An in-syringe ultrasound-assisted emulsification microextraction (USAEME) was developed for the extraction of organophosphorus pesticides (OPPs) from water samples. The OPPs subsequently analyzed gas chromatography (GC) using a microelectron capture detector (μECD). Ultrasound radiation was applied to accelerate the emulsification of μL-level low-density organic solvent in aqueous solutions to enhance the microextraction efficiency of OPPs in the sample preparation for GC-μECD. Parameters affecting the efficiency of USAEME, such as the extraction solvent, solvent volume, pH, salt-addition, and extraction time were thoroughly investigated. Based on experimental results, OPPs were extracted from a 5 mL aqueous sample by the addition of 20 μL toluene as the extraction solvent, followed by ultrasonication for 30 s, and then centrifugation for 3 min at 3200 rpm, offered the best extraction efficiency. Detections were linear in the concentration of 0.01–1 μg/L with detection limits between 1 ng/L and 2 ng/L for OPPs. Enrichment factors ranged from 330 to 699. Three spiked aqueous samples were analyzed, and recovery ranged from 90.1% to 104.7% for farm-field water, and 90.1% to 101.8% for industrial wastewater. The proposed method provides a simple, rapid, sensitive, inexpensive, and eco-friendly process for determining OPPs in water samples.     

Determination of organochlorine pesticides in ground water using solid-phase microextraction followed by dual-column gas chromatography with electron-capture detection

A rapid, sensitive, convenient, and highly quality-assured method is presented for the determination of 19 organochlorine pesticides (OCPs) in small samples (10 ml) of ground water. Samples are initially fortified with 2,4,5,6-tetrachloro-m-xylene (surrogate) and decachlorobiphenyl (retention time marker), then extracted with a 30-micron thickness polydimethylsiloxane solid-phase microextraction fiber. The analytes collected are thermally desorbed in a heated gas chromatographic inlet, separated using independent fused-silica capillary columns ("primary" and "confirmatory"), and detected using electron-capture detection. Two independent statistical procedures were used to evaluate the detection limits, which typically range between 10 and 40 ng l-1, for these analytes. Method performance was also evaluated using two additional protocols employing "performance evaluation" samples, in which authentic ground water samples were fortified to ca. 100 ng l-1 in each of at least six OCPs. The method satisfies additional strict criteria based on uniformity of fiber performance and minimal degradation of the thermally-sensitive analytes endrin and DDT.     

Determination of 4-methyl-cis-hexahydrophthalic anhydride in human blood by gas chromatography with electron-capture detection.

A gas-chromatographic technique using 63Ni electron-capture detection was applied to the determination of 4-methyl-cis-hexahydrophthalic anhydride in the blood of workers occupationally exposed to this airborne agent. The detection limit was 0.24 nmol ml-1. For occupational exposure to between 0.14 and 0.31 mg m-3 of the anhydride, the anhydride concentration in the workers' blood samples ranged from 3.4 to 10.7 nmol ml-1. The results are consistent with earlier findings in animal exposure experiments and support the view that the hydrolysis of the anhydride in a biological medium is not spontaneous, but might be an enzyme-catalysed reaction. The resulting dicarboxylic acid is excreted by the kidneys without further conjugation reactions.     

Determination of estradiol 2- and 4-hydroxylase activities by gas chromatography with electron-capture detection

A highly sensitive assay has been developed for measuring the rate of formation of 2-hydroxyestradiol and 4-hydroxyestradiol from estradiol by microsomal preparations. Catechol estrogens were converted to heptafluorobutyryl esters, which were separated by capillary column gas chromatography and quantified using electron-capture detection. 2-Hydroxyestradiol 17-acetate was used as an internal standard. The identity of catechol estrogen derivatives was verified by gas chromatography-mass spectrometry using negative-ion chemical ionization. Estrogens were identified by negative molecular ions and/or by characteristic fragments. This procedure permits quantification of catechol estrogens at the subpicogram level. The assay was validated by comparing estrogen 2- and 4-hydroxylase activities in microsomes from hamster and rat liver with values reported previously.     

Determination of endotoxins by gas chromatography: evaluation of electron-capture and negative-ion chemical-ionization mass spectrometric detection of halogenated derivatives of beta-hydroxymyristic acid

The sensitivity and selectivity of gas chromatography for analysing several halogenated ester derivatives of beta-hydroxymyristic acid were studied using both selected-ion monitoring detection with negative-ion chemical-ionization mass spectrometry and electron-capture detection. Six different derivatization methods were compared with respect to yield, chemical stability and formation of by-products. Procedures for removal of excess reagents using disposable silica columns and thin-layer chromatography were elaborated. The 3-O-pentafluorobenzoyl-methyl ester was the preferred derivative since it provided high sensitivity and had the molecular ion as the base peak in the mass spectrum. The detection limit was 0.5 pg with electron-capture detection and 0.3 pg with the mass spectrometric system. Using beta-hydroxymyristic acid as a chemical marker it was possible to detect Escherichia coli endotoxin in aqueous solution at a level of 1 ng/ml.     

Determination of propafenone in biological fluids by fused-silica capillary gas chromatography using electron-capture detection

A gas-liquid chromatographic method with electron-capture detection using a capillary column with the inlet in the splitless injection mode is reported for the assay of propafenone. A 25 m X 0.31 mm cross-linked, 5% phenylmethylsilicone-coated fused-silica capillary column was employed for all analyses. The present method provides improved selectivity and sensitivity over other existing gas chromatographic and high-performance liquid chromatographic (HPLC) methods. Linearity was observed in the ranges 2.5-50 and 10-100 ng/ml. The coefficient of variation was found to be less than 10% over the concentration ranges studied. Application of the developed method is demonstrated by measuring serum propafenone concentrations over 24 h in a normal healthy volunteer after a single oral dose of propafenone and by measuring trough plasma propafenone concentrations at steady state in patients receiving this new antiarrhythmic drug. Validity of the present method is further demonstrated by comparison of analytical results obtained from measurement of patient samples using a modified published HPLC method.