DEVELOPMENT AND VALIDATION OF A QUANTITATIVE METHOD FOR DETERMINATION OF ORGANOPHOSPHORUS INSECTICIDES IN MILK BY HEADSPACE SOLID PHASE MICROEXTRACTION COMBINED WITH GAS CHROMATOGRAPHY-FLAME THERMIONIC DETECTION

摘要

Organophosphorus pesticides (OPPs) are widely used in agriculture and for cow ectoparasite control because they are less liposoluble like than the organochlorine pesticides and are easily degraded to less harmful compounds. However, in spite of their low persistence may represent a risk for human health. The ability of OPPs to covalently link proteins can lead to persistence of the pesticide in milk; in fact it has been proved that casein, mainly with its seryland phosphoseryl residues, can bind with OPPs. Also, the lipophylic nature of most OPPs favours their accumulation in a fatty matrix such as milk. Therefore, milk can be one of the human dietary sources of OPPs. The detection of these residues in milk is important to correctly evaluate the overall consumer risk with particular attention to the safety of infants and children.Problems due to the complexity of these matrices, along with the presence of interferences make the analyses of samples of animal origin difficult. In this sense, Headspace Solid - Phase Microextraction (HS-SPME) can represent a method of choice. The advantage of Headspace approach is the elimination of coextraction of undissolved particles and non-volatile components in the sample matrix. Therefore, HS-SPME could be a potentially useful tool to selectively extract the organophosphorus insecticides, as the fibre is not directly submerged in the matrix. The objective of this study were to develop a HS-SPME based method in order to eliminate the fat removing procedure in the milk sample preparation prior to analysis of 11 OPs and 4 with GC-FTD and to reduce co-extracted interferences. The target compounds were extracted from milk by a Polydimethylsiloxane fiber (100um thickness) at 75°C. The effects of extraction time, temperature, agitation method, salt concentration, dilution and fat content on the analyte recovery were studied and optimized. A standard addition method was used for the quantification of the organophosphorus insecticides in milk samples in order to suppress matrix effects. The accuracy of the analysis at three concentration levels varied between 73 and 108 % while repeatability and reproducibility expressed as % R.S.D. were below 10 %. Low LODs that ranged between 0.006-0.010 mg Kg~-1 can be achieved, while the LOQs ranged from 0.016 to 0.030 mg Kg~-1.