Sample Preparation in the Analysis of Pesticides Residue in Food by Chromatographic Techniques

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Food samples present an enormous challenge to analytical chemists in their efforts to determine residues of pesticides at trace levels to satisfy food safety regulations in EU, USA and Japan. The wide array of food matrices from liquids to solids require different sample preparation techniques for accurate and reproducible results with chromatographic techniques such as Gas chromatography(GC) and High Performance Liquid Chromatography (HPLC). In addition, there exists a wide range of pesticides which are used legally for crop protection and their residue content in food must be accurately monitored for safe consumption. The GC and HPLC techniques with different types of detector systems can provide such analysis at trace levels to fulfill the maximum residue levels(MRL) as per the food safety regulations in these countries. However, the accurate and reproducible results often depend upon the sample preparation techniques associated with the different food matrices. Sample preparation has always been regarded as the bottleneck in the analytical laboratory performing numerous analyses, but it is the key to accurate analysis. In this regard, as per pesticide residue analysis, where not only the physical volume of the analyses can be enormous but also the number of pesticides involved can range from a selected few to a broad spectrum depending on the food source. This will usually necessitate the employment of different sample preparation methods for different targeted pesticides as well as the multitude of food matrices. It has been estimated that the sample preparation step in most determinations consume approximately 60 – 70 % of the total time required for the analysis. It must be able to produce analytically accurate results and be economically efficient for routine analysis. In addition, it must be safe and easy to perform. Most sample preparation procedures for GC and HPLC determination follow the basic steps as outlined below: 1. The food sample is homogenized or blended to obtain a uniform matrix. 2. This will be followed by extraction of the pesticide residue with solvents. 3. A cleanup step is employed to remove interfering matrix components from the GC or HPLC chromatograms.