DETERMINATION OF ARYLPHENOXYPROPIONIC HERBICIDES IN WATER BY LIQUID-CHROMATOGRAPHY ELECTROSPRAY MASS-SPECTROMETRY

A very sensitive and specific analytical procedure for determining ary lphenoxypropionic herbicides in aqueous environmental samples, using p neumatically assisted electrospray (ESI) liquid chromatography-mass sp ectrometry (LC-MS) is presented. Arylphenoxypropionic acids are a new class of herbicides used for the selective removal of most grass speci es from any nongrass crop. These herbicides are commercialized as herb icide esters. It has been shown that the ester derivatives undergo fas t hydrolysis in the presence of vegetable tissues and soil bacteria, y ielding the corresponding free acid. The analytical procedure involves passing 1 l of surface or ground water and 2 l of drinking-water samp les, through a 0.5-g graphitized carbon black (GCB) extraction cartrid ge. A conventional 4.6-mn I.D. reversed-phase LC C-18, operating with a 1 ml/min mobile phase flow-rate, was used for chromatographing the a nalytes. A flow of 200 mu l/min of the column effluent was diverted to the ESI source. The ESI source was operated in positive-ion mode for neutral pesticides and in negative-ion mode for acid pesticides. For i on-signal optimization, the effect of the concentration of the acid in the mobile phase on the response of the ESI-MS detector was investiga ted. By evaluating the specificity and sensitivity of the method, the effects of varying the orifice plate voltage on the production of the diagnostic fragment and the response of the MS detector were also inve stigated. For the analyte considered, the response of the mass detecto r was linearly related to the amount of the analyte injected between 1 and 200 ng. In all cases, recoveries of the analytes were better than 91%. The limit of detection (signal-to-noise ratio=3) of the method f or the pesticides considered in drinking water samples was estimated t o be about 3-10 ng/l. (C) 1998 Elsevier Science B.V. All rights reserv ed.