Development and validation of a method for determination of residues of 15 pyrethroids and two metabolites of dithiocarbamates in foods by ultra-performance liquid chromatography-tandem mass spectrometry

This paper reports a novel approach for the detection, confirmation, and quantification of 15 selected pyrethroid pesticides, including pyrethins, and two metabolites of dithiocarbamates in foods by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS). The proposed method makes use of a modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) procedure that combines isolation of the pesticides and sample cleanup in a single step. Analysis of pyrethroids and dithiocarbamate metabolites was performed by UPLC-MS-MS operated with electrospray and atmospheric pressure chemical ionization, respectively. Two specific precursor-product ion transitions were acquired per target compound in multiple reaction monitoring (MRM) mode. Such acquisition achieved the minimum number of identification points according to European Commission (EC) document no. SANCO/10684/2009, thus fulfilling the EC point system requirement for identification of contaminants in samples. The method was validated with a variety of food samples. Calibration curves were linear and covered from 1 to 800 mu g kg(-1) in the sample for all target compounds. Average recoveries, measured at mass fractions of 10 and 100 mu g kg(-1) for pyrethroids and 5 and 50 mu g kg(-1) for dithiocarbamate metabolites, were in the range of 70-120% for all target compounds with relative standard deviations below 20%. Method limits of quantification (MLOQ) were 10 mu g kg(-1) and 5 mu g kg(-1) for pyrethroids and dithiocarbamate metabolites, respectively. The method has been successfully applied to the analysis of 600 food samples in the course of the first Hong Kong total diet study with pyrethroids and metabolites of dithiocarbamates being the pesticides determined.