Analytical method validation qualitative test

As an analytical approach to residue analysis, immunoassay methods are not well characterized, and no validation protocols have been established. The Association of Official Analytical Chemists, whose primary purpose is validation of analytical methods, established a Task Force on Test Kits and Proprietary Methods (2), which has addressed some of the issues relating to immunoassay methods. The International Union of Pure and Applied Chemistry s Commission on Food Chemistry has established a Working Group on Immunochemical Methods, whose first project is to develop draft guidelines on criteria for evaluation, validation, and quality control for r o-immunoassay methods (10). Similar guidelines for EIAs will also be developed. These documents will assist in development and standardization of requirements for precision for both between-laboratories and within-laboratory andyses, accuracy, and ruggedness, and— for qualitative methods— false positive and false negative rates. 

Similar to quantitative methods, qualitative tests should also undergo a method validation. The measuring system of a qualitative test usually transforms a quantitative result into a negative or positive report or in some cases a semi-quantitative outcome however, the absolute numerical concentration of the analyte itself is not reported. Qualitative tests can be validated by using a series of samples with known concentrations of analyte that fall either side of the positive-negative cut-off. These known values may be assigned by an alternative method, or may be reference material. It is particularly important to assess reproducibility of results around a concentration of the analyte of interest that is clinically important such as around a diagnostic cut-off. A method comparison study can also be undertaken with a comparator. The new method can usually be implemented when predefined criteria are fulfilled. 

Principles and Characteristics Whereas parameters most relevant to method development are considered to be accuracy, system precision, linearity, range, LOD, LOQ, sensitivity and robustness, method validation parameters are mainly bias, specificity, recovery (and stability of the analyte), repeatability, intermediate precision, reproducibility and ruggedness. However, method development and validation are highly related. Also, validation characteristics are not independent they influence each other. Acceptance criteria for validation parameters should be based on the specification limits of the test procedure. Quantitation and detection limits need a statement of the precision at their concentration levels. Procedures used for validation of qualitative methods are generally less involved than those for quantitative analytical methods. According to Riley [82], who has discussed the various parameters for validation of quantitative analytical methods, the primary statistical parameters that validate an analytical method are accuracy and precision. 

Sampling frequency depends on the rate/extent of dermal absorption. Appropriate analytical techniques, e.g. scintillation counting, HPLC or GC, should be used. Their validity, sensitivity and detection limits should be documented in the report. When an increase in sensitivity is needed, the test substance should, whenever possible, be radiolabeUed. Qualitative or semi-quantitative methods such as microautoradiography can be useful tools for skin distribution assessments. 

---