Sample preparation by matrix solid-phase dispersion for determination of organochlorine and pyrethroid residues in garlic

Abstract

Matrix solid-phase dispersion (MSPD) is a simple and fast sample preparation technique that employs very small amount of organic solvent. Sample is dispersed uniformly in the solid support where the matrix and interferences are trapped within the sorbent and the target analytes can be eluted selectively with suitable organic solvent. This research developed a MSPD procedure for the extraction and cleanup of twenty six organochlorine and pyrethroid residues (OCPYs) in garlic for GC-µECD analysis. Optimization of key parameters included types of solid support, and types and volume of the elution solvent. The optimum MSPD condition used 5 g of sorbent 1:1 (w/w) florisil:siliga gel) and 30 mL of hexane to elute twenty six OCPYs. The method has been validated and achieved quantitative analysis down to their maximum residue limit. The linearity range from 0.005-0.50 mg/L, method detection limit is in range of 0.003-0.004 mg/kg and its method quantitation limit is 0.01 mg/kg. Intra –assay precision, intermediate precision and relative standard deviation were less than 7.5 % when compared with the value from Horwitz equation. For all compounds at 0.01, 0.05 and 0.10 mg/kg, recoveries obtained were generally in the range of 83.6-107.0. The method was used to test 4 samples from 2 Thai markets. All of them were contaminated with Cypermethrin in low concentration and lower than MRLs of EU regulations. The approach can be used as a standard method for quantitative analysis of organochlorine and pyrethroid pesticides in Garlic.