Pesticide testing by enzyme immunoassay at trace levels in environmental and agricultural samples

Pesticide testing is currently dominated by such chromatographic methods as high performance liquid chromatography (HPLC) and gas chromatography (GC). A generation of analytical chemists have experience with such methods and a vast amount of historical and reliable data has been accumulated with these methods and associated instrumentation. However, in the last 3–5 years there has been an increasing number of reports on the use of enzyme immunoassay (EIA) techniques for detecting pesticides. EIA technology is a well-known, accurate and reliable technique, widely utilized and in itself historically proven in both human and veterinary diagnostics. It is therefore logical and in fact inevitable that they would find application in the ‘environmental diagnostic’ marketplace. EIAs are antibody-based techniques combining the analyte-binding properties of the antibody with the signal amplication advantages of an enzyme. Although many varieties of EIAs (or ‘ELISA’: Enzyme Linked Immunosorbent Assays) exist, the format described herein utilizes antibody-coated plastic tubes or microwells. The antibodies, to various pesticides, were raised in rabbits and immobilized onto the solid phases by a proprietary process that provides long term stability and reactivity. The sample analyte (pesticide) plus peroxidase ‘tagged’ pesticide reagent (‘conjugate’) are simultaneously added to the tube or well and ‘compete’ for the antibody. Following a wash step and substrate addition, color is generated and the results interpreted: the lower the color, the greater the pesticide concentration. The concentration of analyte can be determined by comparison of the sample color to a standard curve prepared in parallel. EIAs have a number of advantages when compared to HPLC and GC methods. They are simple (suitable for ‘field’ use), sensitive (with detection limits of) ∼ 10–20 parts per trillion), specific (to classes or even individual compounds), rapid (results as quickly as 6–7 min) and inexpensive (typically US$5–$15). However, they are not always the most suitable method and care must be taken to avoid ‘false-positives’ by including appropriate controls. Immunoassays for the very low detection of atrazine (water and milk), procymidone and benomyl (wine) and paraquat (water) will be described together with correlative chromatography data.