Analytical method validation as per WHO Technical Report Series, No. 937

  • Analytical method validation as per WHO Technical Report Series, No. 937
  • Principle
  • General
  • Pharmacopoeial methods
  • Non-pharmacopoeial methods
  • Method validation
  • Characteristics of analytical procedures

This appendix presents some information on the characteristics that should be considered during validation of analytical methods. Approaches other than those specified in this appendix may be followed and may be acceptable. Manufacturers should choose the validation protocol and procedures most suitable for testing of their product.

The manufacturer should demonstrate (through validation) that the analytical procedure is suitable for its intended purpose.

Analytical methods, whether or not they indicate stability, should be validated.

The analytical method should be validated by research and development before being transferred to the quality control unit when appropriate.

There should be specifications for both, materials and products. The tests to be performed should be described in the documentation on standard test methods.

Specifications and standard test methods in pharmacopoeias (“pharmacopoeial methods”), or suitably developed specifications or test methods (“non-pharmacopoeial methods”) as approved by the national drug regulatory
authority may be used.

Well-characterized reference materials, with documented purity,should be used in the validation study.

The most common analytical procedures include identification tests,assay of drug substances and pharmaceutical products, quantitative tests for content of impurities and limit tests for impurities. Other analytical procedures
include dissolution testing and determination of particle size.

The results of analytical procedures should be reliable, accurate and reproducible. The characteristics that should be considered during validation of analytical methods.

Verification or re-validation should be performed when relevant,

For example,

when there are changes in the process for synthesis of the drug substance,

changes in the composition of the finished product,

changes in the analytical procedure; when analytical methods are transferred from one laboratory to another; or when major pieces of equipment instruments change.

The verification or degree of re-validation depend on the nature of the change(s).

There should be evidence that the analysts, who are responsible for certain tests, are appropriately qualified to perform those analyses (“analyst proficiency”).

Pharmacopoeial methods
When pharmacopoeial methods are used, evidence should be available to prove that such methods are suitable for routine use in the laboratory (verification).

Pharmacopoeial methods used for determination of content or impurities in pharmaceutical products should also have been demonstrated to be specific with respect to the substance under consideration (no placebo interference).

Non-pharmacopoeial methods
Non-pharmacopoeial methods should be appropriately validated.

Method validation
Validation should be performed in accordance with the validation protocol.

The protocol should include procedures and acceptance criteria for all characteristics. The results should be documented in the validation report.

Justification should be provided when non-pharmacopoeial methods are used if pharmacopoeial methods are available. Justifi cation should include data such as comparisons with the pharmacopoeial or other methods.

Standard test methods should be described in detail and should provide sufficient information to allow properly trained analysts to perform the analysis in a reliable manner. As a minimum, the description should include the chromatographic conditions (in the case of chromatographic tests), reagents needed, reference standards, the formulae for the calculation of results and system suitability tests.

Characteristics of analytical procedures
Characteristics that should be considered during validation of analytical methods include:
— specificity
— linearity
— range
— accuracy
— precision
— detection limit
— quantitation limit
— robustness.

Accuracy is the degree of agreement of test results with the true value, or the closeness of the results obtained by the procedure to the true value.

It is normally established on samples of the material to be examined that have been prepared to quantitative accuracy. Accuracy should be established across the specified range of the analytical procedure.

Note: it is acceptable to use a “spiked” placebo where a known quantity or concentration of a reference material is used.

Precision is the degree of agreement among individual results. The complete procedure should be applied repeatedly to separate, identical samples drawn from the same homogeneous batch of material. It should be
measured by the scatter of individual results from the mean (good grouping) and expressed as the relative standard deviation (RSD).

Repeatability should be assessed using a minimum of nine determinations covering the specifi ed range for the procedure e.g. three concentrations/three replicates each, or a minimum of six determinations at 100% of
the test concentration.

Intermediate precision expresses within-laboratory variations (usually on different days, different analysts and different equipment). If reproducibility is assessed, a measure of intermediate precision is not required.

Reproducibility expresses precision between laboratories.

Robustness (or ruggedness) is the ability of the procedure to provide analytical results of acceptable accuracy and precision under a variety of conditions. The results from separate samples are influenced by changes in the operational or environmental conditions.

Robustness should be considered during the development phase, and should show the reliability of an analysis when deliberate variations are made in method parameters

Factors that can have an effect on robustness when performing chromatographic analysis include:
— stability of test and standard samples and solutions.
— reagents (e.g. different suppliers).
— different columns (e.g. different lots and/or suppliers).
— extraction time.
— variations of pH of a mobile phase.
— variations in mobile phase composition.
— temperature; and
— fl ow rate.

Linearity indicates the ability to produce results that are directly proportional to the concentration of the analyte in samples. A series of samples should be prepared in which the analyte concentrations span the claimed range of the
procedure. If there is a linear relationship, test results should be evaluated by appropriate statistical methods.

A minimum of five concentrations should be used.

Range is an expression of the lowest and highest levels of analyte that have been demonstrated to be determinable for the product. The specified range is normally derived from linearity studies.

Specificity (selectivity) is the ability to measure unequivocally the desired analyte in the presence of components such as excipients and impurities that may also be expected to be present. An investigation of specificity
should be conducted during the validation of identification tests, the determination of impurities and assay.

Detection limit (limit of detection) is the smallest quantity of an analyte that can be detected, and not necessarily determined, in a quantitative fashion.

Approaches may include instrumental or non-instrumental procedures and could include those based on:
— visual evaluation.
— signal to noise ratio.
— standard deviation of the response and the slope.
— standard deviation of the blank; and
— calibration curve.

Quantitation limit (limit of quantitation) is the lowest concentration of an analyte in a sample that may be determined with acceptable accuracy and precision.

Approaches may include instrumental or non-instrumental procedures and could include those based on:
— visual evaluation.
— signal to noise ratio.
— standard deviation of the response and the slope.

— standard deviation of the blank; and
— calibration curve.

Characteristics (including tests) that should be considered when using different types of analytical procedures
are summarized in Table 1.

Analytical -

System suitability testing
System suitability testing is an integral part of many analytical procedures.
The tests are based on the concept that the equipment, electronics, analytical operations and samples to be analysed constitute an integral system that can be evaluated as such. System suitability test parameters that need to be
established for a particular procedure depend on the type of procedure being evaluated, for instance, a resolution test for an HPLC procedure.



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Reference: WHO Technical Report Series, No. 937.

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