DEVELOPMENT OF ENZYME-LINKED IMMUNOSORBENT ASSAYS FOR THE INSECTICIDECHLORPYRIFOS .2. ASSAY OPTIMIZATION AND APPLICATION TO ENVIRONMENTAL WATERS

Monoclonal antibody-based enzyme-linked immunosorbent assays (ELISA) t o chlorpyrifos were optimized for the analysis of this insecticide in environmental water samples. By optimizing the immunoreagent condition s and the composition of the competition buffer, assays with up to 1 o rder of magnitude better sensitivities were obtained. Reduction of the detergent (Tween 20) concentration provided most of the sensitivity i mprovement. Other factors studied, such as pH and ionic strength, beha ved consistently with the nonpolar nature of the analyte and contribut ed in lesser extent to improve assay characteristics. Under optimized conditions, the chlorpyrifos concentration giving 50% reduction of max imum ELISA signal (I-50) was in the 0.8-1;0 nM range, and the assays s howed acceptable specificity for both chlorpyrifos and chlorpyrifos-me thyl. Preliminary evaluation of assay performance in several water sam ples showed the absence of significant matrix effects for both formats evaluated. ELISAs provided a limit of detection of 0.10-0.14 mu g/L a nd a working range in the 0.21-2.50 mu g/L range and allowed the direc t determination of submicrograms per Liter chlorpyrifos in environment al water samples with acceptable analytical parameters.