Protocol, method validation accuracy requirements

While methods validation and accuracy testing considerations presented here have been frequently discussed in the literature, they have been included here to emphasize their importance in the design of a total quality control protocol. The Youden two sample quality control scheme has been adapted for continuous analytical performance surveillance. Methods for graphical display of systematic and random error patterns have been presented with simulated performance data. Daily examination of the T, D, and Q quality control plots may be used to assess analytical performance. Once identified, patterns in the quality control plots can be used to assist in the diagnosis of a problem. Patterns of behavior in the systematic error contribution are more frequent and easy to diagnose. However, pattern complications in both error domains are observed and simultaneous events in both T and D plots can help to isolate the problems. Point-by-point comparisons of T and D plots should be made daily (immediately after the data are generated). Early detection of abnormal behavior reduces the possibility that large numbers of samples will require reanalysis. 

Execution of the method validation protocol should be carefully planned to optimize the resources and time required to complete the full validation study. For example, in the validation of an assay method, linearity and accuracy may be validated at the same time as both experiments can use the same standard solutions. A normal validation protocol should contain the following contents at a minimum ... 

The ISO definition of validation is confirmation by examination and provision of objective evidence that the particular requirements of a specified intended use are fulfilled [15]. Method validation is needed to confirm the fitness for purpose of a particular analytical method, that is, to demonstrate that a defined method protocol, applicable to a specified type of test material and to a defined concentration rate of the analyte —the whole is called the analytical system — is fit for a particular analytical purpose [4]. This analytical purpose reflects the achievement of analytical results with an acceptable standard of accuracy. An analytical result must always be accompanied by an uncertainty statement, which determines the interpretation of the result (Figure 6). In other words, the interpretation and use of any measurement fully depend on the uncertainty (at a stated level of confidence) associated with it [8]. Validation is thus the tool used to demonstrate that a specific analytical method actually measures what it is intended to measure and thus is suitable for its intended purpose [11,55,56]. 

The calibration protocol outlined in Section II.G.4, is valid in both the laboratory and in the process environment, at least upon initial process analyzer installation. Once installed, however, the probe head is relatively inaccessible, at least for frequent checks or recalibrations. Pixel phase-stepping approaches as proposed by Mann and Vickers [227] for use in the laboratory for improved wavelength accuracy are time-consuming, costly, and add moving parts to a process analyzer system [126]. With this in mind, it is necessary to address the subject of Raman analyzer calibration from the point of view of the industrial process environment. This necessarily involves compromises with respect to the ideal calibration methods discussed previously [126,191,265]. There are several levels of compromises that can be considered, each of which involves a different level of cost, complexity, and accuracy. Ultimately, the intended process application and its associated accuracy requirements must determine the calibration approach selected. 

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. 

Once a new analytical method has been developed, it must be optimized and standardized to meet the purposes for which it was developed. Validation studies confirm that a new assay has met its required performance specifications, and must be done before the analytical procedure can become a routine laboratory protocol. There are multiple approaches to validating analytical methods. The most common is to compare results from the new method with results obtained using an established, or reference, assay. Alternatively, standard reference materials (e.g. standards certified by NIST) can be analyzed by the new method to demonstrate its accuracy. When available, authentic specimens should be tested and compared against a previously validated protocol. 

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. 

Prior to its use a method has to be validated. Validation is the formal proof that the method is suitable for the intended purpose. This requires that all steps and parameters of the method have been clearly specified in a written method description, any necessary equipment was qualified, and acceptance criteria for each validation point have been agreed upon. For quantitative methods the International Conference on Harmonization (ICH) has issued specific guidelines for setting up a validation protocol and for parameters that have to be validated for different applications. These include specificity, accuracy, precision, LOD, LOQ, linearity, and range as well as robustness. The only required validation parameter for qualitative methods is specificity. 

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