Analytical Methods for Residues Determination

Differences exist among regulatory agencies in establishing the relationship of the marker residue to total residues, and standardizing the conditions under which analytical methods will be required. Some countries require microbiological 

The reliability of a method can be determined by assessing certain method performance criteria including, specificity, accuracy, precision, limit of detection and quantitation, sensitivity, applicability, and practicability as appropriate (13). This very often requires that an extensive collaborative study be undertaken to obtain the necessary data. Methods that have successfully undergone this performance review testing have been considered to be validated for the purpose of the analysis (14). 

The ideal validated method would be the one that has progressed fully through a collaborative study in accordance with international protocols for the design, conduct, and interpretation of method performance studies. A typical study of a determinative method conducted in accordance with the internationally harmonized International Organization for Standardization (ISO)/International Union for Pure and Applied Chemistry (IUPAC)/AOAC International (AOAC) protocol would require a minimum of up to five test materials including blind replicates or split-level samples to assess within-laboratory repeatability parameters, and eight participating laboratories (15). Included with the intended use should be recommended performance criteria for accuracy, precision and recovery. 

Validation attempts in tlie field of drug residue analysis have demonstrated that die requirement for a full collaborative trial at the ideal level, while desirable, is sometimes impractical. Limiting factors for completing ideal multilaboratory validation studies are usually the high cost, lack of sufficient expert laboratories willing to participate in such studies, and overall time constraints. Hence, a three-laboratory validation study is often applied (16). 

In cases in which tliis less stringent model cannot be used, alternative validation schemes may be used (17). These include a two-laboratory validation protocol similar to the AOAC International Peer Verified Method Protocol, or a singlelaboratory validation approach. With any of tlie alternative validation schemes, the Joint FAO/IAEA Expert Consultation on Validation of Analytical Methods 

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