Quality Assurance—Does the Method Still Work

Once a method has been validated, an important aspect of applying it is to assure that it is working properly. Quality assurance (QA) is the implementation of procedures to ensure and document that the method continues to perform as required and is part of the responsibility of the quality assurance unit. It includes written documentation of validation of the method, procedures followed, and the sample custody chain. A number of quality control procedures are implemented, based on quantitative measurements. Typical quality control activities are listed below. 

QA is an ongoing checking procedure to assure proper performance of a method. 

One way of documenting performiance of the laboratory is to participate in collaborative interlaboratory studies. An official body provides aliquots of the same homogeneous material to laboratories for analysis. The goal is to compare results among laboratories and the uncertainties in the results. The mean of the results of the participating laboratories can be used as the reference, if the actual concentration is not known. Or better, a certified reference material whose concentration and certainty is known (not to the participating laboratories) is used. The latter is particularly more informative if the laboratories use different methods. 

One way of expressing the results of a collaborative testing exercise is to report the laboratory s z score, a measure of its deviation from the standard deviation of the known concentration  

GOOD LABORATORY PRACTICE QUALITY ASSURANCE OF ANALYTICAL MEASUREMENTS 

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QUALITY ASSURANCE—DOES THE METHOD STILL WORK ... 

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