Automated Trace Analysis of Pesticides in Water

An automated system appropriate for the analysis of a variety of chemical classes of pesticides and conversion products in water is presented. The system is based on the online solid-phase extraction (SPE) of target solutes followed by high-performance liquid chromatography (HPLC) tandem photodiode array/postcolumn derivatization/fluorescence detection (PDA/PCD/FLD). SPE is carried out on Hysphere-GP (10 � 2 mm) reversed-phase cartridges using the automated PROSPEKT system. Aliquots of 100 mL acidified (pH 3.0) samples are processed. The on-line HPLC analysis is carried out on a C18 analytical column eluted with a binary gradient of 10 mM phosphate buffer and an acetonitrile/water (90:10 v/v) mixture. Solutes are tentatively identified by tandem PDA/PCD/FLD. The PDA detector is used as a general-purpose detector; the FLD is useful for confirmation of N -methyl-carbamate and N -methyl-carbamoyloxime pesticides, which are postcolumn derivatized with o -phthalaldehyde and N,N -dimethyl-2-mercaptoethylamine-hydrochloride after hot alkaline hydrolysis. The entire analytical system is controlled and monitored by a single computer operated by the chromatographic software. Solute recoveries from water samples are better than 80%, except for some highly polar and highly hydrophobic compounds; for these compounds, the respective recoveries are in the range of 10–80%. The limits of identification, based on the PDA detector, are in the range 0.02–0.1 �g/L for the majority of target analytes; the limits of detection of the PCD/FLD system are in the range 0.005–0.02 � g/L for all amenable analytes.