Simple removal of humic and fulvic acid interferences using polymeric sorbents for the simultaneous solid-phase extraction of polar acidic, neutral and basic pesticides

A styrene-divinylbenzene (St-DVB) sorbent with a specific surface area of ca. 1000 m(2) g(-1) packed in a disposable cartridge was investigated and compared with C-18 silicas and other St-DVB polymers such as those entrapped in Empore disks and the LC-grade PRP-1 or PLRP-S with specific surface areas around 500 m(2) g(-1). A much higher retention was obtained for polar pesticides and acidic pesticides were also retained in their ionic form. The recoveries obtained on percolating 500 mi of drinking water samples at pH 7 spiked with a mixture of seventeen acidic, neutral and basic pesticides through a cartridge packed with 200 mg of SDB-1 sorbent (1060 m(2) g(-1)) were above 80% for each analyte. Another important result was that humic and fulvic acids were not co-extracted and co-eluted on percolating a sample adjusted to pH 7, so no clean-up was necessary. Application to the analysis of a 500-ml river Seine water sample spiked at 0.1 mu g l(-1) showed that detection limits in this range can be obtained without any additional clean-up step.