Non-invasive identification of chemical compounds by energy dispersive X-ray fluorescence spectrometry, combined with chemometric methods of data evaluation

Chemicals from customers' returns have to be analyzed before they can be re used as raw materials in production. A procedure for non-invasive qualitati ve analysis of compounds in a closed container based on energy dispersive X -ray fluorescence (EDXRF) spectrometry is described. EDXRF was chosen as me thod for noninvasive analysis of chemicals through PE bottle walls without opening the bottle. This analysis aims for a quick proof of correspondence between the declaration of a reagent on the label of the bottle and its con tent. This analytical result cannot be achieved by a mere evaluation of cha racteristic element lines in EDXRF-spectra in combination with the method o f matrix correction or the method of mean atomic number. These methods take into account only a small part of the total information available in an X- ray spectrum. It is shown here that valuable additional information is extr actable from the spectral ranges of the Compton-scattering and Rayleigh-sca ttering areas by the use of methods of multivariate data analysis, especial ly by principle component analysis (PCA). Regularized dis criminant analysi s (RDA) was employed to establish a classification scheme for unknown sampl es.