| Abstract: | Determination of Pesticides in Water by On-line Solid-phase Extraction and HPLC-DAD This paper describes an HPLC on-line procedure for the determination of 29 relevant pesticides in water by diode-array detection using a compact HPLC-system with integrated column-switching. The sample – 5 mL – is injected with a large volume injection system on a precolumn cartridge (RP-C18). Enriched compounds are eluted in frontflush mode by columnswitching to a microbore column and separated with a gradient water/acetonitrile. During desorption the precolumn cartridge is heated at 80°C resulting in a comparable efficiency to the separation with direct injection. The procedure is fully automated for continuous monitoring of drinking-, ground-, and surface water with low contamination levels. Sample preparation is limited to a filtration step with an anion-exchange membrane filter to reduce natural contaminations e.g. humic acids simultaneously. For a concentration of 50 ng/L, the signal to noise ratio varies from 3:1 (Ethidimuron) up to 25:1 (Chloridazon). The standard deviations compare to the standardized HPLC-method DIN EN ISO 11369; the recovery rates are 100% and reproducible. The method was successfully tested on ruggedness with several sequences from a monitoring program. The precolumn cartridge needs replacement after 100 sample injections. Finally, this method was coupled with a benchtop mass-spectrometer (electrospray mode) without changing the chromatographic conditions. With selected ion monitoring (SIM) selectivity and detection sensitivity could be improved considerably compared to DAD-detection. |
