Pressurized liquid extraction of chlormequat and mepiquat from cereal flours followed by LC tandem MS analysis

A new analytical method for the rapid extraction and unequivocal confirmation of herbicides chlormequat (CQ) and mepiquat (MQ) in wheat flours and various flours utilized in infant foods was developed. The extraction procedure is based on pressurized liquid extraction (PLE), using ethanol as extractant at high pressure and temperatures; the extraction rapidity is combined with the elevated selectivity and sensibility of the LC-MS-MS. Analytes were separated by ion exchange chromatography and d9-chlormequat was used as internal standard. Mass-spectrometric detection was conducted with a triple quadrupole equipped with a TurboIonSpray source operating in positive ionization mode. Two Selected Reaction Monitoring (SRM) were chosen for each analyte and the developed analytical method was validated by evaluating recovery, precision, linear dynamic range, sensitivity, limit of detection (LOD) and limit of quantitation (LOQ). Special emphasis was placed on the versatility and robustness of automated PLE for routine trace determination of the selected analytes; moreover, the use of ethanol allowed one to inject the sample directly, avoiding the evaporation step. In particular, the study addresses the impact of the food matrix on ion suppression by comparing solvent calibration curves with those obtained by blank extracts, spiked with analytes. Calibration curves in matrix displayed a slope lower of about 20% than that noticed in the solvent. Recoveries ranged from 83 to 99% at a fortification level of 10 ppb, corresponding to the maximum residue limit established by the European Union, while intra-day precision was less than 10% for all samples. The developed method was applied to detect the incidental presence of MQ and CQ in different cereal flours. In particular, traces of the selected herbicides were detected in about 50% of baby foods.