X-RAY-FLUORESCENCE ANALYSIS FROM THE INFORMATION-THEORY POINT OF VIEW

Information theory is a fundamental concept for a general comparison of different methods of chemical analysis. It delivers the information content of an analysis in binary digits (bits). In contrast to the normal interpretation of the result of an analysis, information theory demonstrates the gain of information about the composition of a sample before and after the analysis has been made. In the first section of this paper, the useful information content of a quantitative analysis of a completely unknown sample with an X-ray spectrometer is derived. It is shown that the decision for the discrimination steps has to be made on the basis of a geometrical rather than an arithmetical series, as is recommended in the present literature. According to this thesis, an XRF-equipment can deliver an information quantity of about 940 bits. In the second section, examples are given of the information content obtained in the field of process control. Here the analyst has a lot of information on the composition of the sample in advance and the analysis provides much less information content than in case of an unknown sample. In three examples, concerning the manufacturing of stainless steel brass, and cement, it is shown, that the gain in information by the XRF-equipment lies between 3 and 10 bits. © 1979.