Validation of Analytical Methods

Principle - Certain methods need to be followed for validating analytical methods but still other approaches can be considered. Manufacturers must choose a validation protocol and certain procedures that are suitable for testing the products. Analytical methods must be validated for their stability by research and development by manufacturers.

General – Both materials and products should have specifications which are properly documented. Either they should be pharmacopoeial methods or non- pharmacopoeial methods (should be approved by national drug regulatory authority).

In the course of validation reference materials should be properly documented regarding their purity standards.

Some of the analytical methods are identification tests, quantitative and limit tests for impurities, assay for pharmaceutical products and drug substances, dissolution tests and particle size determination.

The results obtained by various analytical methods should be accurate, reliable and reproducible.

Revalidation or Verification should be done only when major changes occur in instruments or parts of an equipment or analytical method or composition of finished product or transfer from lab to another.

Analysts should be properly qualified to perform tests.

Method validation: Pharmacopoeial methods or non- pharmacopoeial methods should be properly validated by protocol with proper justification. Protocol should cover detailed procedures with information on reagents, reference standards, and formulae with system suitable tests.

Characteristics of Analytical Methods

Analytical methods should have certain characteristics which are

1. Accuracy
2. Precision
3. Repeatability
4. Intermediate position
5. Reproducibility
6. Robustness
7. Linearity
8. Range
9. Specificity
10. Detection limit
11. Quantitation limit

1. Accuracy: It is degree of agreement or closeness of test results with the true value. Accuracy is defined on samples of materials to be examined.
2. Precision: It is degree of agreement among the individual results. This procedure should be applied to identical samples separately which are drawn from a homogenous batch. It is measured by the scattering of individual results from mean value which is expressed as relative standard deviation (RSD).
3. Repeatability: it is assessed by nine determinations covered over a specific range.
4. Intermediate precision: it expresses variations within laboratory. This procedure might not be required if reproducibility is determined.
5. Reproducibility: it measures degree of precision between laboratories.
6. Robustness: The degree of accuracy and precision provided by analytical results under deliberate varied conditions. This procedure should be followed during developmental phase. Various factors effect robustness during chromatographic analysis like reagents and different columns from different suppliers, variations in p^H or composition of mobile phase, temperature, extraction time, flow rate and stability of standard and test samples.
7. Linearity:  It depicts the ability to indicate results in proportion to concentration of samples analyte.
8. Range: It gives the minimum and maximum levels of analyte for a product.
9. Specificity: It is measurement of desired analyte together with excipients and impurities. This procedure should be followed during assay and impurity determination and validation of identification tests.
10. Detection Limit: The minimum quantity of analyte which can be detected quantitatively. It is also applicable to instrumental or non-instrumental procedures based on calibration curve, signal/noise ratio, visual evaluation, standard deviation of response and the slope, standard deviation of blank.
11. Quantitation limit: the minimum quantity of analyte which can be determined with accuracy and precision. This limit can be exercised for instrumental or non-instrumental procedures based on signal/noise ratio, calibration curve, standard deviation of blank, visual evaluation, standard deviation of response and slope.

    Type of analytical procedure	Identification	Testing for impurities	Testing for impurities	Assay -dissolution - content/ potency
    Characteristics		Quantitative tests	Limit tests
    Accuracy	-	+	-	+
    Precision
    Repeatability	-	+	-	+
    Intermediate precisiona	-	+	-	+
    Specificity	+	+	+	+
    Detection limit	-	-b	+	-
    Quantitation limit	-	+	-	-
    Linearity	-	+	-	+
    Range	-	+	-	+

-        Characteristic is not evaluated

+       Characteristic is normally evaluated

^a              Intermediate precision is not needed when reproducibility is performed

^b             May be needed in some cases

• Based on procedure to be evaluated for equipment, analytical operations, electronics and samples, test parameters are established by system suitability testing.

Analytical, validation, revalidation, accuracy, precision, linearity, range

• supplementary guidelines on good manufacturing practices: validation. world health organization. who technical report series, no. 937, 200. http://apps.who.int/prequal/info_general/documents/trs937/who_trs_937-annex4.pdf. accessed may 18, 2016.