COMPARISON OF GAS-CHROMATOGRAPHY MASS-SPECTROMETRY AND IMMUNOASSAY TECHNIQUES ON CONCENTRATIONS OF ATRAZINE IN STORM RUNOFF

Gas chromatography/mass spectrometry (GC/MS) and enzyme-linked immunos orbent assay (ELISA) techniques were used to measure concentrations of dissolved atrazine in 149 surface-water samples. Samples were collect ed during May 1992-September 1993 near the mouth of the White River (I ndiana) and in two small tributaries of the river. GC/MS was performed on a Hewlett-Packard 5971A(1) with electron impact ionization and sel ected ion monitoring of filtered water samples extracted by C-18 solid phase extraction; ELISA was performed with a magnetic-particle-based assay with photometric analysis. ELISA results compared reasonably wel l to GC/MS measurements at concentrations below the Maximum Contaminan t Level for drinking water set by the U.S. Environmental Protection Ag ency (3.0 mu g/L), but a systematic negative bias was observed at high er concentrations. When higher concentration samples were diluted into the linear range of calibration, the relation improved. A slight posi tive bias was seen in all of the ELISA data compared to the GC/MS resu lts, and the bias could be partially explained by correcting the ELISA data for cross reactivity with other triazine herbicides. The highest concentrations of atrazine were found during the first major runoff e vent after the atrazine was applied. Concentrations decreased througho ut the rest of the sampling period even though large runoff events occ urred during this time, indicating that most atrazine loading to surfa ce waters in the study area occurs within a few weeks after applicatio n.