Liquid chromatography mass spectrometry tandem for multiresidue determination of selected post-emergence herbicides after soil column extraction

A multianalyte method has been developed for the confirmation and quantitat ion of 16 selected post-emergence (POE) herbicides (three imidazolinones (I MIs), three diphenyl ethers (DPhEs), six sulfonylureas (SUs), two aryloxyph enoxypropionic acids, and two triazolopyrimidine sulfonanilides (SAs)) in s oil samples. The method proposed takes advantage of the specificity provide d by sample preparation and liquid chromatography tandem mass spectrometry (LC-MS/MS). The analytes are extracted using soil column extraction (SCE) a nd the extracts are cleaned up using Carbograph-1 cartridge. The final extr act is evaporated to dryness, redissolved in water/acetonitrile (80/20, v/v ) acidified with 15 mmol/l formic acid and analyzed using LC-MS/MS interfac ed via a turbo ion spray (TISP). To establish the suitable extraction condi tions for sample preparation, several variables affecting the performance o f SCE, such the use of extractant, temperature, sample size, extractant vol ume and solvent flow rate, have been studied. Maximum yields were obtained by extraction with a solution of 0.1 mol/l KH2PO4, pH=8, at ambient tempera ture. In order to evaluate the matrix effect in SCE of POE herbicides, reco very experiments were performed for soil samples with different physical an d chemical characteristics. The results of SCE were compared with the resul ts of classical ultrasonication (USE) and microwave-assisted solvent extrac tion (MASE). The recovery data including precision were evaluated statistic ally. It was found that recoveries and precision of SCE compared with USE a nd MASE gave better results. Using SCE, the average recoveries of POE herbi cides in the different samples ranged between 63 and 99%. The relative stan dard deviation ranged between 3 and 8%. Low detection limits at the parts p er billion (ppb) level can be obtained. For confirmation, the parent ion an d the product ions were monitored in the multiple reaction monitoring (MRM) mode. (C) 2000 Elsevier Science B.V. All rights reserved.