Simultaneous determination of presticide residues in vegetables by solid-phase extraction cleanup and gas chromatography

Cha, Lian Kuet. (2003) Simultaneous determination of presticide residues in vegetables by solid-phase extraction cleanup and gas chromatography. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

A simple and rapid method has been developed for the determination of organophosphorus (OP), organochlorine (OC), and pyrethriod (PY) pesticides in vegetables using solid-phase extraction (SPE) cleanup. The results obtained were compared with the established routine method without cleanup for OP pesticides and silica gel cleanup for OC and PYpesticides. Residues were extracted with acetone and methylene chloride lJfxtracts were cleanup up by SPE mixed-mode column using quaternary amine and aminopropyl (SAXINH2) or octadecyl (CI8) sorbents. The pesticides were determined by gas chromatography with flame photometric detector for OP pesticides and micro-electron capture detector (u-ECD) for OC and PY pesticides. The results from the SAXINH2study showed that the recoveries obtained for the eleven OP pesticides tested except for the polar one such as methamidophos and dimethoate (depending on the matrix) were within the acceptable range of 70 % to 120 %. This method offers a cleaner extract than the routine method which do not requires cleanup. The extract obtained can be injected directly into the ECD for the OC and PY determination. Recoveries obtained for the six OC pesticides using the same method were comparable with the silica gel method. For the five PYpesticides tested, the recoveries obtained were also corresponding to the silica gel method. For the CI8 cleanup method, the recoveries obtainedfor eleven OP pesticides tested except methamidophos were within the acceptable range. However, the recoveries obtainedfor the nine OC pesticides using the CI8 method were lower than those obtained from silica gel method. For the five PYpesticides tested, the recoveries obtained using this method were comparable to the silica gel method. In spite of the limited range of this study, it can be predicted that the SPE CI8 and SAXINH2 cleanup methods can be extrapolated to a wider range of other OP, OC and PY pesticides. These methods can also be used for other fruits and vegetables. The benefits of the SPE method compared to the routine method were the used of organic solvents is reduced, possibility of concentration of the samples, less sorbent used, no cross contamination, shorter analysis time and the technique is easy to automate.

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