![\"fig_5_part_ii.png\"](\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/fig_5_part_ii.png\" "\\"fig_5_part_ii.png\\"")
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Figure 1.\u00a0A possible sequence of operations and decisions in LC\u2013MS method validation. All steps are explained in detail in upcoming chapters. ST<\/em>% refers to stability in per cents, explained in section 8.3. LoF stands for Lack-of-Fit test, explained in 3.3. CRM stands for certified reference material.<\/h4>\n\u00a0<\/p>\n
Before starting a validation, a clear validation\u00a0plan is compiled, which consists of the reason for validation, planned experiments, as well as expected outcomes \u2013 requirements that need to be met by the method. Requirements often result from guidelines or from other regulatory documents (directives, standards etc.). A validation\u00a0plan depends on each of the\u00a0different method\u00a0under development and it takes into account all the specific aspects related to that method. After carrying out the necessary experiments, a decision must be made if the results are satisfying and consequently if the method is fit for purpose. Validation is documented in a validation report.<\/p>\n
Guidelines generally give recommendations how to\u00a0evaluate\u00a0each performance parameter separately. At the same time, guidance on how to decide\u00a0about the whole method\u2019s validation is usually very general: validation has to demonstrate that the values of all evaluated parameters are satisfactory. Few different cases arise.<\/p>\n
\n- (a) When methods are applied in the scope of standards, laws or directives, then requirements from those documents, if present, must be followed and a\u00a0decision on validation should be based on these documents. When a\u00a0decision on validation suitability is based on the guidelines, then the decision\u00a0for each parameter must be given\u00a0separately\u00a0according to the requirements.<\/li>\n
- (b) Sometimes the client can specify the requirements, then\u00a0client\u2019s requirements are superior to those in the guidelines.<\/li>\n
- (c) If there are no external requirements, then the analyst can set up the requirements himself\/herself based on his\/her knowledge of the subject.<\/li>\n<\/ul>\n
Validation should start with evaluating analyte stability and method selectivity as all\u00a0other parameters strongly depend on these. For example, if an\u00a0analyte extensively decomposes in the autosampler, no linear relation can be achieved. In that case, non-linear calibration models need to be considered. Consequently, we propose an estimation of linearity as the next step, because for an evaluation of trueness and precision, we need to know the linear\/working range of the method. We propose robustness studies as the last step of validation. It is sometimes suggested to test robustness as one of the first things in method validation or in the end of the method development phase. We find it important to have some insight, as to which are the most important performance characteristics (e.g. closest to the legal limits or the requirements of the client) before deciding which of the method performance characteristics are varied during the robustness studies.<\/p>\n
Not only validation but also an appropriate documentation of the validation is required for an adequate interpretation as well as on the validity of the obtained results. As the last stage of validation, an assessment of validity (fitness for the intended purpose) of the method should be given, based on the validation results.\u00a0<\/p>\n
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Validation should start with evaluating analyte stability and method selectivity as all\u00a0other parameters strongly depend on these. For example, if an\u00a0analyte extensively decomposes in the autosampler, no linear relation can be achieved. In that case, non-linear calibration models need to be considered. Consequently, we propose an estimation of linearity as the next step, because for an evaluation of trueness and precision, we need to know the linear\/working range of the method. We propose robustness studies as the last step of validation. It is sometimes suggested to test robustness as one of the first things in method validation or in the end of the method development phase. We find it important to have some insight, as to which are the most important performance characteristics (e.g. closest to the legal limits or the requirements of the client) before deciding which of the method performance characteristics are varied during the robustness studies.<\/p>\n
Not only validation but also an appropriate documentation of the validation is required for an adequate interpretation as well as on the validity of the obtained results. As the last stage of validation, an assessment of validity (fitness for the intended purpose) of the method should be given, based on the validation results.\u00a0<\/p>\n