02/24/2009
Validation and uncertainty study of a comprehensive list of 160 pesticide residues
A rapid and sensitive liquid chromatography-tandem mass spectrometry method, in electrospray ionization positive mode, has been developed for the determination of 160 selected multi-class pesticides over a 33-min run time. Extractswere obtained using the acetonitrile-based QuEChERS (quick, easy, cheap, effective, rugged and safe) sample preparation technique. The validation study was carried out on tomato, pear and orange matrices following DG SANCO/2007/3131 of the European Quality Control uidelines. These matrices represent highwater, high sugar and high acidic content commodities, respectively. Matrix influence on recoveries and its effects on ionization were evaluated for the three matrices. Ten out of the 160 pesticides showed very low intensity, linearity and/or sensitivity problems. Linearity was studied in the 5-500 mycrogram kg1 concentration range. Soft (<20%), medium (20-50%), and strong (>50%) matrix effects were obtained for 69%, 20%, and 11% of the studied compounds, respectively. Recoveries were investigated at the 10 and 100 mycrogram kg1 levels, and depending on the commodity, 97%, 98% and 97% of the compounds in tomato, pear and orange, respectively, were in the 70-120% range. More than 90% of the investigated compounds had less or equal to a 5 mycrogram kg1 limit of detection in the studied matrices. The relative standard deviations obtained exceeded 20% in only very few cases. The overall standard deviation obtained in the survey study (0.1551) was used for the method's uncertainty estimation. The expanded uncertainty resulted as being 0.3002 (coverage factor K = 2, confidence level 95%). The method was applied on 59 real samples from 14 different kinds of fruits and vegetables. Thirty-three compounds were detected in 50 positive samples.
Source: Community Reference Laboratories for Residues of Pesticides