Determination of Acetanilide Degradates in Ground and Surface Waters by Direct Aqueous Injection LC/MS/MS

Abstract

Acetanilide herbicides are widely used throughout the United States to control annual grasses in corn, soybeans and other crops. The herbicides studied, include the acetanilides; acetochlor, alachlor, metolachlor, propachlor and the acetamide; dimethenamid. The biological degradation of these herbicides produces a myriad of polar metabolites the most prominent of which are the ethanesulfonic acids (ESA) and oxanilic acids (OX) moieties. These degradates have been found in surface waters from agricultural runoff and in shallow groundwater due to leaching through vulnerable soils. Several less significant degradates have recently been identified and incorporated into a single multi-residue methodology. A high throughput method has been developed for the analysis of fourteen soil degradates of the specified herbicides. The method uses direct aqueous injection (DAI) liquid chromatography / mass spectrometry / mass spectrometry (LC/MS/MS) to analyze these materials without any sample pretreatment or concentration. MS/MS provides a very specific and highly sensitive mode of detection using TurboIonSpray in the negative ion mode. Thirteen of the fourteen degradates were validated at the 0.05 µg/L level in three different water matrices, raw surface water, finished surface water (drinking water) and groundwater.