Parameters for Method Validation

For an efficient validation process, it is important to specify the right validation parameters and acceptance criteria. The method’s performance parameters and limits should be based on the intended use of the method. It is not always necessary to validate all analytical parameters available for a specific technique.

For example, if the method is to be used for qualitative trace level analysis, there is no need to test and validate the method’s limit of quantitation, or the linearity over the full dynamic range of the equipment. The more parameters, the more time it will take to validate.

The selection of validation parameters and acceptance criteria should be based on business, regulatory and client requirements and should be justified and documented.

 ICH validation characteristics

Type of analytical procedure	Identification	Testing  for impurities	Assay - content/potency
characteristics		quantitat.   limit
Accuracy	-	+            -	+
Precision     Repeatability     Interm.Precision	- -	+            -        + (1)       -	+                       + (1)
Specificity (2)	+	+            +	+
Detection Limit	-	- (3)        +	-
Quantitation Limit	-	+            -	-
Linearity	-	+            -	+
Range	-	+            -	+

-      signifies that this characteristic is not normally evaluated

+     signifies that this characteristic is normally evaluated

(1)   in cases where reproducibility (see glossary) has been performed, intermediate precision is not needed

(2)   lack of specificity of one analytical procedure could be compensated by other supporting analytical procedure(s)

(3)   may be needed in some cases

Specificity is the ability to assess unequivocally the analyte in the presence of components which may be expected to be present. Typically these might include impurities, degradants, matrix, etc.

The accuracy of an analytical procedure expresses the closeness of agreement between the value which is accepted either as a conventional true value or an accepted reference value and the value found.

The precision of an analytical procedure expresses the closeness of agreement (degree of scatter) between a series of measurements obtained from multiple sampling of the same homogeneous sample under the prescribed conditions. Precision may be considered at three levels:  repeatability, intermediate precision and reproducibility (also called ruggedness) 

The  detection limit of an individual analytical procedure is the lowest amount of analyte in a sample which can be detected but not necessarily quantitated as an exact value.

The quantitation limit of an individual analytical procedure is the lowest amount of analyte in a sample which can be quantitatively determined with suitable precision and accuracy. The quantitation limit is a parameter of quantitative assays for low levels of compounds in sample matrices, and is used particularly for the determination of impurities and/or degradation products.

The linearity of an analytical procedure is its ability (within a given range)  to obtain test results which are directly  proportional to the concentration (amount) of analyte in the sample.

The range of an analytical procedure is the interval between the upper and lower concentration (amounts) of analyte in the sample (including these concentrations) for which it has been demonstrated that the analytical procedure has a suitable level of precision, accuracy and linearity.

The robustness of an analytical procedure is a measure of its capacity to remain unaffected by small, but deliberate variations in method parameters and provides an indication of its reliability during normal usage.

USP validation characteristics

Parameter	Assay (cat-I)	Assay (cat-II)		Assay (cat-III)
		Quantitative	Limit tests
Accuracy	Yes	Yes	*	*
Precision	Yes	Yes	Yes	Yes
Specificity	Yes	Yes	Yes	*
Limit of detection	No	No	Yes	*
Limit of quantitation	No	Yes	Yes	*
Linearity	Yes	Yes	Yes	*
Range	Yes	Yes	*	*
Ruggedness	Yes	Yes	Yes	*

Cat-I: Quantification of major compounds

Cat-II: Impurities

Cat-III: Performance characteristics

* May be required

According to the ICH, accuracy, any type of precision and limits of detection and quantitation are not required if the analytical task is for identification purposes. For assays in USP Category 1, the major component or active ingredient to be measured is normally present at high concentrations; therefore, validation of limits of detection and quantitation is not necessary.

Acceptance criteria for the specifications also depend on the intended use of the method.

In practice:

After reviewing the method validation parameters of ICH and USP, we finally concluded the following parameters for method validation.

Accuracy, specificity(with forced degradation), Linearity, Precision(system and sample), Robustness(method parameter variations and Solution and mobile phase stability) Ruggedness and system suitability for Assay method validation.

Accuracy, specificity(with forced degradation), Linearity, Precision(system and sample), Limit of detection, Limit of quantification(precision and accuracy at LOQ level), Robustness(method parameter variations and Solutions and mobile phase stability) Ruggedness and system suitability for Related substances method validation.