Analytical Results in Relation to Fixed Values

The relation of measured results to given values, e.g., critical levels, legally fixed values, regulatory limits, maximum acceptable values, is of continual relevance in analytical chemistry. In the analytical reality, the problematic nature of detection leads to the test statistics, strictly speaking to the t-test (Currie [1995, 1997] Ehrlich and Danzer [2006]). By means of that, it is tested, if the determined analytical result is significantly different from the average blank of the critical value, respectively. 

In the same way, the relation of measured results to limits of various kind (critical levels, xCl) can be treated in general. The situation is shown in Fig. 8.3. 

Frequently, limit values are given as a numerical value without any exceeding level. Then, according to the t-statistics, a significant exceeding has to be stated if x — Ax xCl as illustrated in Fig. 8.3a. On the other hand, 

Comparison of test values with a conventional true value ( reference value ) of a (certified) reference material (RM, CRM). In method development and validation of analytical procedures, the comparison of experimental results with standards of diverse kind (laboratory standards, certified reference materials, primary standards) plays an essential role. The decision as to whether an experimental result hits the reference value depends not only from the result itself but also from its uncertainty interval. 

When working with standards, there are two cases regarding their precision  

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