Methods for Checking Accuracy

As mentioned earlier, the analyst must take care that the results of analysis are reliable (i.e., both accurate and precise). Good precision of determinations obtained using a given method is not enough reason for uncritical satisfaction. There are known cases in which a laboratory provided very precise results that were, however, far from the true value [8, 11, 15]. Although precision can easily be checked internally, for example, by making several repetitions of the determination and calculation of standard deviation, confidence level, and so on, checking accuracy is a much more difficult task. Several approaches are possible  

The use of CRMs (method d) is accessible for most laboratories. If an analyst determining an analyte (e.g., an element in the CRM) is obtaining correct results (i.e., in agreement with the certificate) it can be expected that the results of determinations of this element in other samples are also reliable. The requirement, however, is that the general composition of the analyzed samples and the concentration of the element(s) being determined are similar to those in the CRM. 

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