Validation of a quick and easy (QuEChERS) method for the determination of pesticides residue in dried herbs

Validation experiments were conducted of a simple, fast and inexpensive method for the determination of 71 pesticides fortified at 0.006 2 mg/kg in dried herbs samples (caraway, dry mint and chamomile matrices). The method is known as the quick, easy, cheap, effective, rugged and safe (QuEChERS) method for pesticide residues in herbs. The procedure involved the extraction of samples with water and acetonitrile, followed by a liquid-liquid partitioning step and phase separation by adding buffer–salt mixture, the extract was decanted into a tube containing primary secondary amine (PSA) sorbent plus anhydrous MgSO 4 , which constituted a cleanup procedure called dispersive solid-phase extraction (dispersive-SPE). After a second shaking and centrifugation step, an aliquot of the clear solution was evaporated in presence of tetradecane, then re-dissolved in hexane/ acetone and injected into GC-NPD for determination of organophosphorus and organonitrogen pesticides. For determination of organochlorine and pyrethroids pesticides using GC-ECD, extra cleanup step was performed using solid phase extraction with florisil and silica gel cartridge. The recoveries at different concentration levels (0.006 2 μg/g) ranged from 70 to 120%. The repeatability expressed as relative standard deviation ranged (RSD = 1–22 %, n = 6). The measurement uncertainty expressed as expanded uncertainty and in terms of relative standard deviation (at 95% confidence level) was within the range of ± 38%. This multi residues method, which determines the residues of sixty seven pesticides in herbs sample, was introduced for validation into the scope of the Central Lab of Residue Analysis of Pesticides and Heavy Metals in Food. It was accredited in 2009 by the Finnish Accreditation Service body (FINAS) according to the requirements of the international standard ISO/IEC 17025.