Determination of sulfonic acid degradates of chloroacetanilide and chloroacetamide herbicides in groundwater by LC/MS/MS.

An analytical method is presented which permits qualitative and quantitative analysis of sulfonic acid degradates of three chloroacetanilide herbicides (acetochlor, alachlor, and metolachlor) and one chloroacetamide herbicide (dimethenamid) in groundwater at trace levels with determination by LC/MS/MS. The analytes were isolated from groundwater by solid-phase extraction (SPE). The final samples were analyzed by reversed-phase HPLC with MS/MS detection utilizing a pneumatically assisted, and heat-assisted electrospray interface (TurboIonSpray). Unique precursor/production pairs were obtained in the MS/MS mode which permitted conclusive identification of each analyte, even when the analytes coeluted. Quantification was performed by generation of an external calibration curve. Excellent linearity was obtained over a calibration range from 0.25 to 10 ng injected on-column, with all linear correlation coefficients exceeding 0.999. Method performance for this analytical procedure was validated by analyzing groundwater samples fortified at levels of 0.1, 1, and 50 ppb. The average recovery at each fortification level for each analyte exceeded 89%. Excellent method precision was demonstrated with percent relative standard deviations of less than 10% for all analytes at all fortification levels.