Development of Methods for Screening Pesticide Residues In Plant Matrices in Ghana

Abstract

TLC has been used in combination with micro-extraction and clean-up methods to provide an alternative cost effective analytical procedure for screening pesticide residues in plant matrices. Thirty-five (35) agrochemicals, which are used in priority crops in Ghana, were used in this study. Ethylacetate extraction in the presence of anhydrous sodium sulphate, followed by gel permeation chromatographic clean up and additional purification on silica gel cartridges provided clean extracts enabling the application of 300mg sample equivalent on the TLC plates. Detection method involving the use of O-tolidine was found to be suitable for general screening of residues, having medium sensitivity for several compounds. The method involving the use of silver nitrate was the only one found to be most suitable for detecting the organochlorine pesticides. Lindane was the most sensitive to this reagent and had a Minimum Detectable Quantity (MDQ) value of 5ng/5 uL. This method was suitable for use on only alumina plates and detection was also possible even under sunlight. The enzyme inhibition methods were very sensitive to the carbamate and phosphoric acid type insecticides with MDQ values between 0.2 and 2000ng. Other detection methods involving p-nitrobenzene, p-dimethylaminobenzaldehyde and photosynthesis inhibition were also tried and discussed. The database developed has been successfully used for screening and semiquantitative determination of some ranges of pesticide residue in soil and plant matrices