High pressure liquid chromatography with ultraviolet absorbance or fluorescence detection of carbaryl in potato and corn.

Carbaryl (1-naphthyl-N-methylcarbamate) was extracted from corn and potato with acetone. The acetone extract was partitioned into methylene chloride-hexane and concentrated for cleanup on a 5% water-deactivated Florisil column. The fraction containing the carbamate was subjected to high pressure liquid chromatographic (HPLC) analysis on a 25 cm LiChrosorb Si60 (5 micron) column (2.2 mm id) by various means. First, the pesticide was analyzed directly with ultraviolet (UV) absorption detection at 254 nm and a mobile phase of trimethyl-pentane-isopropanol (96 + 4). After this, a fluorescent derivative was prepared, using dansyl chloride (5-dimethylaminonaphthalene-1-sulfonyl chloride), and analyzed by HPLC, using trimethylpentane-dioxane (95 + 5) as the mobile phase, with both UV absorption (254 nm) and fluorescence (excitation 365 nm, emission greater than 400 nm) detection. The response/ng for the dansyl derivative with fluorescence detection was 1.3 times greater than that for UV detection and 8 times more sensitive than direct UV detection of the carbamate. About 10 ppb carbaryl could be detected after derivatization in the foods studied; for direct analysis, 30-50 ppb could be detected at a 2:1 signal:noise ratio. Recoveries at 0.1 ppm averaged 90% by direct analysis compared with 78% after derivatization.