Exercise in Quality Assurance: A Laboratory Exercise

A laboratory exercise in quality assurance (QA) of analytical chemistry is presented. Quality assurance is considered by students to be difficult, and it is also a demanding subject to the teachers, owing to the multitude of methods available to the statisticians. In this exercise, it was demonstrated that QA could be accomplished in a straightforward manner if a few guidelines of elementary statistics were followed.

The concentration of iron(III) in a iron–thiocyanate complex was measured by spectrophotometry. The method was chosen as a suitable example that was applicable to both batch experiments and to flow injection analysis (FIA). The purpose of the exercise is to compare the performance of the two independent methods of analysis by QA.

By applying the law of propagation of errors and a lower limit of analysis to the analysis of variance, a satisfactory agreement was obtained between results of batch experiments and those of FIA. However, the batch experiments exhibited superior performance as compared to the performance of the FIA method with respect to sensitivity, limit of detection, lower limit of analysis, and to precision.