Development of a method for the determination of 9 currently used cotton pesticides by gas chromatography with electron capture detection.

A reliable, sensitive, and reproducible method was developed for quantitative determination of nine new generation pesticides currently used in cotton agriculture. Injector temperature significantly affected analyte response as indicated by electron capture detector (ECD) chromatograms. A majority of the analytes had an enhanced response at injector temperatures between 240 and 260 °C, especially analytes such as acephate that overall had a poor response on the ECD. The method detection limits (MDLs) were 0.13, 0.05, 0.29, 0.35, 0.08, 0.10, 0.32, 0.05, and 0.59 ng/mL for acephate, trifuralin, malathion, thiamethozam, pendimethalin, DEF6, acetamiprid, brifenthrin, and λ-cyhalothrin. This study provides a precision (0.17-13.1%), accuracy (recoveries = 88-107%) and good reproducible method for the analytes of interest. At relatively high concentrations, only λ-cyhalothrin was unstable at room temperature (20-25 °C) and 4 °C over 10 days. At relatively low concentrations, acephate and acetamiprid were also unstable regardless of temperature. After 10 days storage at room temperature, 30-40% degradation of λ-cyhalothrin was observed. It is recommended that acephate, acetamiprid, and λ-cyhalothrin be stored at -20 °C or analyzed immediately after extraction.