Determination of bile acids by hollow fibre liquid-phase microextraction coupled with gas chromatography.

A method based on hollow-fibre liquid phase microextraction combined with gas chromatography was developed for determination of specific bile acids in caecal materials of rats. Nine unconjugated bile acids, including the primary bile acids (cholic acid, chenodeoxycholic acid and α-muricholic acid) and the secondary bile acids (lithocholic acid, deoxycholic acid, ursodeoxycholic acid, hyodeoxycholic acid, ß-muricholic acid and ω-muricholic acid) were quantified. Extraction conditions were evaluated, including: sample pH, type of organic solvent and amount of caecal material to be extracted. To compensate for sample matrix effects during extraction the method of standard addition was applied. The satisfactory linearity (r(2)>0.9840), high recovery (84.2-108.7%) and good intra-assay (6.3-10.6%) and inter-assay (6.9-11.1%) precision illustrated the good performance of the present method. The method is rapid, simple and capable of detecting and determining bile acids with limit of detection (LOD) ranged from 0.002 to 0.067µg/mL and limits of quantification (LOQ) varied from 0.006 to 0.224µg/mL. The results indicated that the concentration of some secondary bile acids, which usually are associated with health problems, were lower in rats fed with fermentable dietary fibre compared with a fibre free control diet, while the concentration of primary bile acids, usually connected with positive health effects, were higher in rats fed with diets containing dietary fibre. Of the dietary fibres, guar gum and to some extent the mixture of pectin+guar gum had the most positive effects. Thus, it was concluded that the composition of bile acids can be affected by the type of diet.

Analysis of PAH compounds in soil with on-line coupled pressurised hot water extraction-microporous membrane liquid-liquid extraction-gas chromatography.

Pressurised hot water extraction (PHWE) was coupled on-line with microporous membrane liquid-liquid extraction (MMLLE) and gas chromatography (GC) in the analysis of polycyclic aromatic hydrocarbon (PAH) compounds in soil. The MMLLE serves as a trapping device after the PHWE. Water from PHWE is directed to the donor side of the membrane unit and the analytes are extracted to the acceptor solution on the other side of the membrane. The role of MMLLE is to clean and concentrate the extract, which is then transferred on-line to the GC via a sample loop and an on-column interface using partially concurrent solvent evaporation. Separate optimisation of MMLLE and simulations of the PHWE-MMLLE connection were carried out before the actual on-line coupling. After optimisation of the whole on-line system, the efficiencies of the PHWE-MMLLE-GC and PHWE-solid-phase trap extractions were compared. The PHWE-MMLLE-GC method allowed on-line analysis of soil samples. The method was linear, with limits of detection in the range 0.05-0.13 ng and limits of quantification 0.65-1.66 microg g(-1). Comparison of the results with those obtained by other techniques confirmed the good performance.

Supported liquid membrane extraction of peptides.

The application of supported liquid membrane (SLM) extraction for the enrichment of short peptides is presented. The extraction efficiency is dependent on the pH of donor phase and salt concentration in acceptor phase. Moreover, the extraction efficiency is also influenced by the peptide amino-acid sequence and hydrophobicity.

On-line microporous membrane liquid-liquid extraction for sample pretreatment combined with capillary gas chromatography applied to local anaesthetics in blood plasma.

A new automated procedure for analyzing complex samples has been developed utilizing microporous membrane liquid-liquid extraction (MMLLE) combined with capillary gas chromatography. Some local anaesthetics were used as model compounds in aqueous solution as well as in blood plasma. The MMLLE procedure was performed in a flow system with the sample fed to the donor side of the hydrophobic microporous membrane and with an organic solvent (hexane) in the pores and as the acceptor solution. The analytes in a small volume of sample (< 1 mL) were extracted into the organic acceptor phase which was transferred into the gas chromatographic system by utilizing a loop-type interface compatible with large-volume (300 microL) injection. High selectivity and low carry-over effects were obtained with the system. The detection limits were 0.5-1 ng/mL using 0.5 mL of human plasma, and the precision was approximately 5%. The effects of pH, flow rates, and adsorption of the analytes were evaluated.

Determination of Phenmetrazine in urine by gas chromatography-mass spectrometry.

A sensitive and simple gas chromatographic--mass spectrometric method is described for the determination of the central nervous system (CNS) stimulant phenmetrazine in urine. The extraction and derivatization were combined into a single step with isooctane and methyl chloroformate. The limit of quantitation was 0.05 micrograms/mliters urine, and the method was linear up to 100 micrograms/mliters. The coefficients of variation (CV) for within-day runs were 1.2% and 2.4% (n = 5) for two controls containing 1.0 micrograms/mliters and 50 micrograms/mliters, respectively. During a six-month period, the same controls showed CVs of 9.1% and 8.7%, respectively (n = 40), indicating a somewhat lower between-run precision. Phenmetrazine was present in 83 out of 3000 urine samples that were screened for CNS stimulants during this period, and the concentrations ranged from 0.5-370 micrograms/mliters.

Sample preparation using a miniaturized supported liquid membrane device connected on-line to packed capillary liquid chromatography.

A miniaturized supported liquid membrane device has been developed for sample preparation and connected on-line to a packed capillary liquid chromatograph. The device consists of hydrophobic polypropylene hollow fiber, inserted and fastened in a cylindrical channel in a Kel-F piece. The pores of the fiber are filled with an organic solvent, in this study 6-undecanone, thus forming a liquid membrane. The sample is pumped on the outside of the hollow fiber (donor), and the analytes are selectively enriched and trapped in the fiber lumen (acceptor). With this approach, the volume of the acceptor solution can be kept as low as 1-2 µL. This stagnant acceptor solution is then transferred through capillaries attached to the fiber ends to the LC system. The system was tested with a secondary amine (bambuterol), as a model substance in aqueous standard solutions as well as in plasma. The best extraction efficiency in aqueous solution, with an acceptor volume of 1.9 µL, was 32.5% at a donor flow rate of 2.5 µL/min. At flow rates above 20 µL/min, the concentration enrichment per time unit was approximately constant, at 0.9 times/min, i.e., 9 times enrichment in about 10 min. The overall repeatability (RSD) for spiked plasma samples was ∼4% (n = 12). Linear calibration curves of peak area versus bambuterol concentration were obtained for both aqueous standard solutions and spiked plasma samples. The detection limit for bambuterol in plasma, after 10 min of extraction at a flow rate of 24 µL/min, was 80 nM.

Liquid membrane work-up of blood plasma samples applied to gas chromatographic determination of aliphatic amines.

A technique for sample work-up and enrichment using a supported liquid membrane in an automated flow system, connected to a gas chromatograph, was used for the determination of aliphatic amines in human blood plasma. The amines studied were N,N-dimethylethylamine, triethylamine, N-methylmorpholine, cyclohexylamine and N,N-dimethylcyclohexylamine. An efficient clean-up of the complex plasma matrix was achieved, resulting in identical blank chromatograms for plasma samples and aqueous solutions. Different parameters influencing the efficiency and selectivity of the extraction procedure were experimentally studied and theoretically explained. The detection limit depends on the extraction flow-rate and the available sample volume. With 1 ml of sample and a flow-rate giving an extraction time of 16 min, the detection limit was ca. 5 ppb (5 micrograms/l); with 4 ml of sample and a lower flow-rate, sub-ppb detection limits could be reached in ca. 3 h. Linear calibration curves up to 500 ppb were obtained. Blood plasma samples from volunteers exposed to N,N-dimethylethylamine in air were analysed, and the results compared favourably with independent measurements by another method.

Determination of ethylene glycol in postmortem blood by capillary gas chromatography.

A simple procedure for the determination of ethylene glycol in blood by capillary gas chromatography was developed. The proteins are precipitated by the addition of perchloric acid which includes the internal standard 1,2-butanediol. The extract is neutralized and the solution is directly injected. The assay is linear and the precision, expressed as coefficient of variation, is 4-11% (within run). The detection limit is about 0.05 g/L. The method also seems applicable for the determination of ethylene glycol in urine.

Determination of the vapor pressures of moth sex pheromone components by a gas chromatographic method.

The vapor pressures of decyl acetate, five decenyl acetate isomers, (Z)-7-dodecenyl acetate, and (Z)-9-tetradecenyl acetate have been determined at three to six temperatures in the interval 25-45 °C by a gas Chromatographic method suitable for accurate measurements of the low vapor pressures of moth sex pheromone components at biologically relevant temperatures. The vapor pressure values at 30.5 °C are 3.80 Pa for decyl acetate, 4.08-5.40 Pa for the decenyl acetate isomers, 0.562 Pa for (Z)-7-dodecenyl acetate, and 0.094 Pa for (Z)-9-tetradecenyl acetate. The vapor pressures of the decenyl acetates show a small but significant dependence on the double bond position. Four of the compounds in this study, 10∶Ac,Z5-10∶Ac,Z7-12∶Ac, andZ9-14∶Ac have recently been identified as sex pheromone components of the turnip moth,Agrotis segetum. Large differences between the mole percentages of the component as found in liquid extracts of female abdominal tips and the corresponding mole percentages in the vapor phase are predicted.