Evaluation of atrazine soil extraction methods for the determination by enzyme immunoassay and gas chromatography

Four soil extraction methods were evaluated for the determination of atrazine and other s-triazines by ELISA and GC, using both field-treated and laboratory fortified samples. The most efficient recoveries for atrazine, simazine, and cyanazine from loam soil fortified at concentrations from 0.01 ppm to 1 ppm were obtained by mechanical wrist-action shaker (1 h) using methanol:water and solid phase extraction (SPE) cleanup (standard method). A handshaking extraction (1 min) with acetonitrile:water showed fairly good correlation with the standard extraction method and is suitable for field use with ELISA. Sonication using acetonitrile:water and SPE cleanup was the most efficient extraction method for the dealkylated metabolites (deisopropyl and deethyl atrazine) with recoveries higher than 60%. In general, supercritical fluid extraction (SFE) was as efficient as sonication and handshaking but was more variable. A guideline for validation of immunoassays and methods comparison is given. The sensitivity of the ELISA method was comparable to the GC and was both accurate and precise. Comparison of ELISA and GC determinations of 120 field soil samples and 40 laboratory spiked soil samples extracted with four different methods showed no false negatives or positives with excellent correlations and showed not significant differences (P > 0.05). An evaluation of the cost for GC and ELISA methods was also conducted.