Etiket Arşivleri: Quechers Method

QuEChERS A Mini-Multiresidue Method for the Analysis of Pesticide Residues in Low-Fat Products

1. Aim and Scope

This manuscript describes a method for the analysis of pesticide residues in produce with a low fat content, such as fruits, vegetables, cereals as well as processed products including dried fruit.

2. Short Description

The homogeneous and representative subsample is extracted in frozen condition with the help of acetonitrile. After addition of magnesium sulfate, sodium chloride and buffering citrate salts (pH 5-5.5), the mixture is shaken intensively and centrifuged for phase separation. An aliquot of the organic phase is cleaned-up by dispersive SPE employing bulk sorbents (e.g. PSA, GCB) as well as MgSO4 for the removal of residual water. PSA treated extracts are acidified by adding a small amount of formic acid, to improve the storage stability of certain base-sensitive pesticides. The final extract can be directly employed for GC- and LC-based determinative analysis. Quantification is performed using an internal standard, which is added to the extract after the initial addition of acetonitrile. Samples with a low water content (<80%) require the addition of water before the initial extraction to get a total of ca. 10 mL water. When dealing with samples containing <25% water (e.g. cereals, dried fruit, honey, spices) the size of the analytical sample may have to be reduced (e.g. 1-5 g) depending on the load of matrix-co-extractives expected in the final extracts. A brief overview of the method is shown in the flowchart at the end of this document.

Quechers Method

The QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) method of pesticide residue was developed by Michelangelo Anastassiades and Steven Lehotay in 2003 to make the analysis of pesticide residues easier and cheaper. Earlier methods were difficult and required multiple, tedious steps, which were time consuming and required the use of a considerable amount of solvent and did not always cover a wide range of pesticides, necessitating multiple analyses of a sample. Since its original development, the QuEChERS method has been standardized as the AOAC 2007.01, EN 15662 and the mini-multiresidue method. The QuEChERS method allows the analyst to extract pesticides from a homogenized sample in less than 30 minutes, using a minimal amount of solvent, without utilizing any glassware. A broad range of pesticides have been analyzed using QuEChERS, including non-polar, polar and planar pesticides. Pesticides are extracted from interfering matrix components (sugars, fatty acids, sterols, pigments), allowing analysis by GC and LC chromatography. The QuEChERS methodology thus improves the productivity of the laboratory.

Pesticide Analysis: Classical Multiresidue Methods (MRMs) attempt to cover the analysis of as many pesticides as possible from a single sample preparation. More than one analysis is required to cover all the pesticides that one is interested in testing for with the selectivity and sensitivity required for quantification. When the spectrum of the analytes (pesticides) covered in the MRM is broad, fewer additional methods are required to cover all the analytes of interest. The analysis is more efficient in regards to time, personnel and materials. Early MRM were limited to organochloride pesticides (OC) using the FDA Mill’s method (1) in which OC’s and non-polar pesticides were extracted from non-fatty foods with acetonitrile (MeCN), diluted with water and partitioned into non-polar solvent (ether) (2); relatively polar organophosphorus (OP) pesticides were lost in this method. Intermediate MRM increase the analysis range to include polar organophosphate pesticides (OP). These procedures often changed the handling of the MeCN extract with different partitioning, cleanup and determination (analyses) steps.