By definition, method validation is the confirmation by examination and provision of objective evidence that the particular requirements for a specific intended use are fulfilled. It is basically the process of defining an analytical requirement, and confirming that the method under consideration has capabilities consistent with what the application requires. Inherent in this is the need to evaluate the method’s performance. The judgement of method suitability is important; in the past method validation tended to concentrate only on evaluating the performance characteristics. Method validation is usually considered to be very closely tied to method development. Many of the method performance characteristics that are associated with method validation are usually evaluated, at least approximately, as part of method development. However, it is important to remember that formal validation of the final version of the method (the documented procedure) should be carried out. A method should be validated when it is necessary to demonstrate that its performance characteristics are adequate for use for a particular purpose. For example, it is stated in ISO/IEC 17025 that the laboratory shall validate non- standard methods, laboratory-designed/developed methods, standard methods used outside their intended scope, or amplifications and modifications made to the existing standard methods.

On the other hand, method verification is the process of confirmation, through provision of objective evidence, that specified requirements have been fulfilled. A laboratory may adopt a validated procedure which has been published as a standard, or buy a complete measuring system to be used for a specific application from a commercial manufacturer. In both these cases, basic validation work has already been carried out but the laboratory will still need to confirm its ability to apply the method. This is verification. It means that some experimental work must be done to demonstrate that the method works in the end-user’s laboratory. However, the workload is likely to be considerably less compared to validation of a method that has been developed in-house. A method should be verified when laboratory adopts standard methods, such as those published by, e.g. ISO or ASTM, validation by the laboratory using the method is not necessary. However, the laboratory needs to verify the performance of the method as detailed in ISO/IEC 17025: “The laboratory shall confirm that it can properly operate standard methods before introducing the tests”. Verification is also required when there is an important change such as a new unit of instrument, relocation of equipment, new staff or use new batch of critical reagents.