Comparison of an enzyme immunoassay with gas chromatography for atrazine determination in water and soil

Water and soil samples, fortified with atrazine up to 100 ng per ml and 200 ng per g, respectively, were analysed for atrazine by a commercial immunoassay (IA) kit. The aqueous solution, or water /methanol extract of the soil, was mixed with enzyme conjugate and antibody-coated magnetic particles. After incubation, magnetic separation and washing, the enzyme conjugate was reacted with a colour reagent and the atrazine concentration estimated from a calibration curve of the absorption at 450 nm. The analyses were also carried out by gas chromatography (GC). The mean recoveries from water were 112 and 106 per cent for IA and GC, respectively, and there was excellent correlation between the 2 methods. For soils, recoveries from 3 horizons were 82-135, 71-117 per cent for IA and GC, respectively. Overall, the IA method recovered more atrazine than GC but there was no significant difference between the methods. Field samples with a previous history showed poorer agreement, possibly because of deethylatrazine cross reactivity.