A Comparative study on different types of spe sorbents for trace enrichment of pesticides using the matrix solid phase dispersion (MSPD) technique

Abstract

Three different sorbents, that is bonded silicas (silica C-18, silica C-8), carbon (graphitized non-porous carbon) and polymers (styrene/divinylbenzene copolymer resin) were compared for their enrichment potential for isolating pesticides from different matrices. Extraction was carried out using the Matrix Solid Phase Dispersion technique (MSPD), which performs sample homogenization and extraction in a single step. The twenty pesticides analysed in this project varied in physico-chemical properties and application, and hence the enrichment potential of a wide range of pesticides was evaluated. The pesticides analysed belonged to five chemical groups of pesticides, that is organophosphates, organochlorines, carbamates, pyrethroids and nitrogen containing pesticides. Extraction was carried out from different matrices, that is water, soil, milk, and fruits and vegetables and analysed with high performance liquid chromatography (HPLC) with UV detection. This project also studied matrix effects on the extraction efficiency of the sorbents - dissolved organic content in water, organic matter and particle size in soil, fat content in milk, and pigment content in fruits and vegetables. MSPD extraction gave clean extracts with few interference peaks due to co-extractives and overall acceptable recoveries for all the sorbents used. The styrene/divinylbenzene copolymer gave the highest recoveries overall when compared to the other sorbents. Evaluation of the results was conducted for traceability and validation of the analytical method. The project also evaluated the use of HPLC with UV detection compared to the more popular gas chromatography with element selective detectors. The limit of quantitation (LOQ) obtained in this project ranged between 0.31and4.12mg/L which are significantly higher than typical LOQ values obtained by gas-liquid chromatography (0.02-0 20mg/f,). However, the LOQ's are lower than the maximum residue limits (MRL' s) of most pesticides used in this project, and hence it is possible to use HPLC-UV for pesticide multiresidue trace analysis.