Comparison of enzyme-linked immunosorbent assay and gas chromatography procedures for the detection of cyanazine and metolachlor in surface water samples

Enzyme-linked immunosorbent assay (ELISA) data from surface water reconnais sance were compared to data from samples analyzed by gas chromatography for the pesticide residues cyanazine (2-[[4-chloro-6-(ethylamino)-1,3,5 -triaz in-2-yl]amino]-2-methylpropanenitrile) and metolachlor (2-chloro-N-(2-ethyl -B-methylphenyl)-N-(2-methoxy -1-methylethyl)acetamide). When ELISA analyse s were duplicated, cyanazine and metolachlor detection was found to have hi ghly reproducible results; adjusted R(2)s were 0.97 and 0.94, respectively. When ELISA results for cyanazine were regressed against gas chromatography results, the models effectively predicted cyanazine concentrations from EL ISA analyses (adjusted R2s ranging from 0.76 to 0.81). The intercepts and s lopes for these models were not different from 0 and 1, respectively. This indicates that cyanazine analysis by ELISA is expected to give the same res ults as analysis by gas chromatography. However, regressing ELISA analyses for metolachlor against gas chromatography data provided more variable resu lts (adjusted R(2)s ranged from 0.67 to 0.94). Regression models for metola chlor analyses had two of three intercepts that were not different from 0. Slopes for all metolachlor regression models were significantly different f rom 1. This indicates that as metolachlor concentrations increase, ELISA wi ll over- or under-estimate metolachlor concentration, depending on the meth od of comparison. ELISA can be effectively used to detect cyanazine and met olachlor in surface water samples. However, when detections of metolachlor have significant consequences or implications it may be necessary to use ot her analytical methods.