4.2. Validation Criteria

The main validation criteria widely recommended by various regulatory documents (ICH, FDA, European Union) and commonly used in analytical laboratories are:

• Specificity-selectivity.

• Response function (calibration curve).

• Linearity.

• Precision (repeatability and intermediate precision).

• Accuracy (trueness).

• Measurement error (total error).

• Limit of detection (LOD).

• Limit of quantification (LOQ).

• Assay range.

• Sensitivity.

In addition, according to the domains concerned, other specific criteria can be required:

• Analyte stability.

• Recovery.

• Effect of the dilution.

A full validation is necessary for an analytical procedure to pass from the development phase to the phase of routine analysis. The validation step is not only necessary but also required at the time specifications (tests and acceptance limits) are set up for an active ingredient or a finished product.

The validation criteria mentioned above must be established, insofar as possible, in the same matrix as that of samples to be analyzed. Every new analytical procedure will have to be validated for each type of matrix (e.g., for each type of biological fluid and for each animal species). Nevertheless, the definition of a matrix depends on analyst responsibility. Some matrix regrouping, generally admitted by the profession for an application domain given, can be performed.

This section will focus only on the main criteria that apply to most, if not all, analytical methods and that must be adequately estimated and documented for ensuring compliance to regulations. The criteria that are very analytical, but that have no particular statistical content, will be defined here but not be discussed.

4.2.1. Specificity-Selectivity

The specificity of an analytical procedure is the ability to unequivocally assess the analyte in the presence of components that may be expected to be present. Usually, the analyst must demonstrate that the measured result is directly related to the analyte or product of interest and that other aspects in the sample, such as the matrix, do not interfere with the signal or measurement. For example, selectivity of a chromatographic method is verified typically by showing that the product of interest is clearly separated from all other products.