Development of a Multiresidue Method for Analysis of Acidic Pesticides in Cereals with Liquid Chromatography-Tandem Mass Spectrometry

Abstract: A new method for analysis of acidic herbicides, mostly phenoxy acids and their esters, in cereals with liquid chromatography-tandem quadrupole mass spectrometry (LS-MS/MS) has been developed. Samples were hydrolyzed with sodium hydroxide in order to release covalently bound compounds followed by neutralization and finally extraction with acidified ethyl acetate. The extraction efficiency for both ester formulations and acids were studied. Acceptable results (70-120 %) were obtained for 2,4-D, dichlorprop, MCPA and mecoprop for both esters and acids. However, low recoveries were observed for ester formulations of dicamba, fluroxypyr, fluazifop and haloxyfop, possibly due to the complex structure of the compounds in combination with the matrix and/or incomplete hydrolysis step. The limit of quantification (LOQ) for targeted pesticides was 0.01 mg/kg. The method has been tested in the EU Proficiency Test for cereals with good results.