DETERMINATION OF ACIDIC HERBICIDES USING LIQUID-CHROMATOGRAPHY WITH PNEUMATICALLY ASSISTED ELECTROSPRAY-IONIZATION MASS-SPECTROMETRIC AND TANDEM MASS-SPECTROMETRIC DETECTION

Liquid chromatography-pneumatically assisted electrospray mass spectro metry with negative ionization has been used for the determination of acidic herbicides in ground water. Eighteen pesticides or pesticide de gradation products belonging to several different groups of acidic her bicides (phenoxy acids, sulfonylureas, phenols, etc.) were covered in the study. Optimization of electrospray inlet conditions is described as well as results from investigations of the linearity of the detecto r response. Conditions for tandem mass spectrometry (MS-MS) detection of characteristic daughter ions formed by collision-induced dissociati on (CID) of the parent ion are described and a comparison of obtainabl e instrument detection limits by single MS and MS-MS was made. Detecti on limits using MS in the selected ion monitoring (SIM) mode were gene rally in the order of 1 mu g/l or below, whereas detection limits were three-four times higher using MS-MS detection. A principle of analysi s is proposed based on single quadrupole MS as a method for quantitati ve determination followed by verification of positive findings by CID MS-MS. Application of the method for detecting acidic herbicides resid ues in a ''real-world'' ground water sample is demonstrated. (C) 1998 Elsevier Science B.V.