Determination of microcontaminants in sediments by on-line solid-phase extraction-gas chromatography-mass spectrometry.

Two simple and straightforward analytical procedures for the screening of sediment samples are reported. They involve extraction with ethyl acetate or methanol and subsequent analysis by means of gas chromatography-mass spectrometry (GC-MS) using large-volume injection (LVI) or solid-phase extraction (SPE). The latter, which was originally developed for the analysis of aqueous samples, can be used without any modification. In general, 10 ml of organic solvent were added to 2 g of sediment, and the mixture was shaken and allowed to stand overnight. The methanolic extracts were then diluted in water and subjected to preconcentration and analysis using on-line SPE-GC-MS. The ethyl acetate extracts were injected directly into the GC using LVI. Both methods were used for the detection and identification of microcontaminants during a monitoring study of the river Nitra (Slovak Republic). They included polyaromatic hydrocarbons (PAHs), chlorofluorohydrocarbons, alkoxylated and alkylated phenols and benzothiazole derivatives. Semi-quantitative profiles of the contaminants were constructed and provisionally interpreted. The results indicate that SPE-GC-MS, and also LVI-GC-MS, have good potential for a rapid screening of sediment samples and the identification of microcontaminants. The analytical procedures pose no problems, and the on-line set-up is user-friendly.

On-line combination of aqueous-sample preparation and capillary gas chromatography.

Methods currently in use to combine the preparation of aqueous samples on-line with capillary gas chromatography (GC) comprise heartcut-orientated reversed-phase liquid chromatography-GC and analyte-isolation-orientated analyte extraction-GC. These approaches either use techniques in which water is directly introduced onto the GC column, or an indirect approach in which water is eliminated, i.e., by solid-phase extraction, solid-phase microextraction or liquid-liquid extraction, prior to introduction of the analytes onto the GC column. The latter type of approach is much more successful and user-friendly, and many applications have been reported.

On-line combination of aqueous-sample preparation and capillary gas chromatography.

An overview is presented of methods currently in use to combine the preparation of aqueous samples on-line with capillary gas chromatography. Two approaches can be distinguished: heartcut-orientated reversed-phase liquid chromatography-gas chromatography (GC) and analyte-isolation-orientated analyte extraction-GC. These approaches either use techniques in which water is directly introduced onto the GC column, or an indirect approach in which water is eliminated, i.e., by solid-phase extraction, solid-phase microextraction or liquid-liquid extraction, prior to introduction of the analytes onto the GC column. The latter type of approach is much more successful and user friendly, and many applications have been reported.

Automated on-line solid-phase extraction-gas chromatography with nitrogen-phosphorus detection: determination of benzodiazepines in human plasma.

An automated sample preparation module, the ASPEC (automated sample preparation with extraction columns) was interfaced with a capillary gas chromatograph (GC) by means of a loop-type interface. The system was optimized for the determination of four benzodiazepines in plasma. Extraction from the untreated plasma was carried out on disposable C18 cartridges and involved several washing steps. The analytes were desorbed with 2 ml of ethyl acetate and a 110-microliter aliquot of the eluate was injected into the gas chromatograph via the loop-type interface using fully concurrent solvent evaporation conditions. Detection of the benzodiazepines was carried out with a nitrogen-phosphorus detector (NPD). The ASPEC-GC-NPD was fully automated and could run unattended overnight. With a sample volume of 1 ml the procedure showed good linearity and repeatability in the range 5-50 ng/ml using a sample volume of 1 ml. The limits of detection in plasma were 0.5-2 ng/ml.

Automated on-line dialysis for sample preparation for gas chromatography: determination of benzodiazepines in human plasma.

An on-line dialysis-solid-phase extraction-gas chromatographic (GC) approach has been developed for the determination of drugs in plasma, using some benzodiazepines as model compounds. Clean-up is based on performing the dialysis of 100 microliters samples for 7 min using water as acceptor phase and trapping the diffused analytes on a PLRP-S copolymer precolumn. After drying of the precolumn with nitrogen for 15 min, the analytes are desorbed with ethyl acetate (275 microliters) and injected on-line into the GC system via a loop-type interface. The system provides a very efficient clean-up, and offers the possibility of adding chemical agents which can help to reduce drug-protein binding and, thus, increase sensitivity. To demonstrate the potential of the described approach, the determination of benzodiazepines in plasma at their therapeutical levels is used as an example with flame ionization, thermionic and mass-selective detection.

On-line trace-level enrichment gas chromatography of triazine herbicides, organophosphorus pesticides, and organosulfur compounds from drinking and surface waters.

A simple, selective and precise procedure for the analysis of water samples by on-line solid phase extraction gas chromatography (SPE-GC) is presented. The determination of several triazines, organophosphorus pesticides, sulfur containing compounds in tap water was performed by SPE-GC using polymer-packed precolumns and flame ionization (FID), nitrogen-phosphorus (NPD) or flame photometric (FPD) detection. A cartridge packed with silica was inserted between the precolumn and the gas chromatograph in order to eliminate trace amounts of water present in the ethyl acetate used as desorption solvent. Incorporation of a drying step allowed the retention gap to be used for the analysis of ca. 100 samples without significant deterioration of the chromatographic peaks. Analyte recovery was at least 72% when 10 ml of tap-water sample were analysed. The detection limits for all analytes in tap water were lower than 0.1 microgram l-1, with all detectors used. Although with NPD and FPD, selectivity and sensitivity were markedly better. The SPE-GC-NPD system has also been used for the analysis of surface-water samples from different European rivers.

Determination of oxidized, reduced and protein-bound glutathione in eye lenses by high-performance liquid chromatography and electrochemical detection.

A method for the detection of oxidized, reduced and protein-bound glutathione in eye lenses has been developed. Homogenized lens samples are deproteinated with acetonitrile and perchloric acid. Protein-bound glutathione is reduced by 1,4-dithiothreitol. Separation of the different forms of glutathione and dithiothreitol is performed by ion-pair reversed-phase high-performance liquid chromatography with sodium octylsulphate as the ion-pairing agent. The compounds are detected amperometrically using on-line-generated bromine, which oxidizes thiols and disulphides. In this way two samples can be analysed in triplicate in a single day. The lower detection limits are 80 and 48 nmol per gram wet lens for reduced and oxidized glutathione, respectively. The amounts of free reduced and protein-bound glutathione in calf lenses, determined with this method, are 6.8 +/- 0.4 and 0.96 +/- 0.03 mumol per gram wet lens, respectively. That of oxidized glutathione is less than 0.048 mumol per gram wet lens.