DEVELOPMENT OF A METHOD BASED ON LIQUID-CHROMATOGRAPHY ELECTROSPRAY MASS-SPECTROMETRY FOR ANALYZING IMIDAZOLINONE HERBICIDES IN ENVIRONMENTAL WATER AT PART-PER-TRILLION LEVELS

An evaluation was made of the feasibility of using reversed-phase liqu id chromatography-mass spectrometry with an electrospray interface (LC -ESI-MS) to measure traces of imidazolinone herbicides in different na tural water samples. The imidazolinones are a significant new class of low-use-rate, reduced-environmental-risk herbicides for the protectio n of a wide variety of agricultural commodities. The procedure used in volved passing 0.5, 1, 2 1 of river, ground and drinking water samples , respectively, through a 0.5 g graphitized carbon black (GCB) extract ion cartridge. Analytes were eluted from the GCB surface by 8 mi of a methylene chloride-methanol (80:20, v/v) solution acidified with formi c acid, 25 mM. Recovery was higher than 89% irrespective of the aqueou s matrix in which the analytes were dissolved. A conventional 4.6 mm L D. reversed-phase LC C-18 column operating with a mobile phase flow-ra te of 1 ml/min was used to chromatograph the analytes. A flow of 50 mu l/min of the column effluent was diverted to the ESI source. The effe cts of acid concentration on ESI-MS detector response in the mobile ph ase were investigated. The effects on the production of diagnostic fra gments produced by varying the orifice plate voltage and the response of the MS detector were also evaluated. For the analyte considered, th e response of the mass detector was linearly related to the amount of analyte injected between 1 and 50 ng; The limit of detection (signal-t o-noise ratio=3) of the method for the pesticides considered in drinki ng water samples was estimated to be about 2-5 ng/l. (C) 1998 Elsevier Science B.V.