Determination of neutral chlorinated extractable organic compounds in water samples using large volume on-column injection capillary gas chomatography–mass spectrometry

An automated large volume on-column injection technique (LOCI) for capillary gas chromatography – mass spectrometry, GC-MS, with solvent divert and heated retention gap technology has been used to simplify the method for determining sixteen neutral chlorinated extractable compounds (NCEC) in industrial plant process water samples at a level of 10 ng/L. According to the simplified procedure, 30 mL of water sample is extracted with 5 mL hexane, and 100 μL of the extract analyzed by combining large volume on-column injection with mass-selective detection operated in the selected ion monitoring mode. This combination has enabled simplification of the sample preparation and analysis procedures and provided a fast, labor-saving technique for analyzing water samples. Simplifications include significant reduction of sample and eluent volumes during extraction, and elimination of the Kuderna-Danish evaporative concentration step. The latter simplification has not only resulted in significant time savings, both during the analysis and for subsequent glassware cleaning; analyte losses and the introduction of contaminants and artifacts which may occur during this step have also been eliminated. System behavior, e.g. linearity of detector response, method detection limit, and reproducibility, were evaluated for all sixteen analytes using spiked water samples in the lower ng/L range. The response of the mass detector is linear in the range 5–20000 ppt for all sixteen NCEC investigated. Injection of 100 μL of sample using LOCI makes it possible to achieve an instrument detection limit in the ppt range. The calculated method detection limits are similar to those of the instrument precision and are lower than the required method detection limit of 10 ppt. Extraction efficiency has been maximized by optimizing sample-to-solvent ratio and extraction time. The extraction efficiency seems to be independent of sample-to-solvent ratio in the range of 2. 5 to 6 and increasing the extraction time from 25 to 120 minutes resulted in no significant increase in efficiency. Extraction efficiency also seems to be independent of the concentration of analyte in the water samples. The simplified procedure presented here was automated by means of a laboratory robot and used to generate all the extraction data reported in this manuscript.