ANALYSIS OF PESTICIDES USING LIQUID-CHROMATOGRAPHY ATMOSPHERIC-PRESSURE CHEMICAL IONIZATION MASS-SPECTROMETRY

Seventeen pesticides in five chemical classes (triazines, phenylureas, carbamates, organophosphates, miscellaneous) from the US Environmental Protection Agency's National Pesticide Survey of groundwater contaminants were selected for analysis by atmospheric pressure chemical ionization (APCI-MS). The spectra obtained from most compounds consisted solely of [M + H]+ in positive-ion mode. One example, p-nitrophenol produced only the [M - H]- ion in negative-ion mode. Increasing the potential on the sampling cone effected voltage-dependent fragmentation of all carbamates and alachlor to form diagnostic daughter ions. Detection limits (Limit of detection (LOD), signal-to-noise ratio = 3) in full-scan or selected-ion monitoring mode varied from 0.8-10 ng or 0.01-1 ng, respectively, and calibration curves were highly linear from the LOD to 100 ng. Mobile phase composition (50-100% acetonitrile in water) and flow rate (0.25 and 1.25 mL/min) had small effects on sensitivity of response. These results suggest that the sensitivity of APCI-MS is affected less than that for thermospray and particle beam LC/MS by chemical differences in analyte structure for the pesticide classes tested. The low detection limits, high degree of linearity, the ability to produce diagnostic fragment ions using cone voltage fragmentation and the inter-class versatility suggest that APCI is a valuable technique for multi-residue confirmations of pesticides in groundwater.