The limitations of accurate “thin-film” X-ray fluorescence analysis of natural particulate matter: Problems and solutions

Abstract

The limitations of “thin-film” X-ray fluorescence (XRF) analysis of natural particulate matter have been re-examined theoretically and experimentally. The degree to which elemental signal intensity is absorbed by the sample matrix far exceeds that which has been assumed in most previous field studies. By means of a simplified theoretical model, the magnitude of absorption effects is predicted for various elements in a variety of natural matrices. The non-specialist may quantify potential analytical artefacts by means of the tables, graphs and equations presented here. Relatively simple formulae have been derived by which absorption phenomena may be calculated and corrected for, even in samples characterised by a wide range of particle sizes, multimodal size distributions and chemical inhomogeneity as a function of particle size. The applicability of these formulae to the enhanced accuracy of coastal particulate matter analyses is discussed. Meaningful analyses of filtered particulate samples by XRF procedures are quite feasible; the limitations of the technique, however, are finite and must be considered in detail. Matrix absorption effects, although modified by various physical parameters, are of sufficient magnitude to render the term “thin-film” inappropriate to the analysis of natural particulates.