The use of synchrotron micro-XRF for characterization of the micro-heterogeneity of heavy metals in low-Z reference materials

Synchrotron mu-XRF (X-ray fluorescence analysis) is a trace-level micro-ana lytical method that allows one to quantitatively measure the degree of hete rogeneity of inorganic trace constituents in a number of reference material s. In the present study, low atomic number materials containing trace level s of heavy metals are concerned. The measurements involve an extensive seri es of local analyses, performed in identical conditions at different locati ons on the material. In order to be able to detect low levels of sample het erogeneity, the experimental set-up must permit the collection of spectral data in a highly repeatable manner. In this paper, a procedure for determin ing the homogeneity of materials on the basis of a series of individual ana lysis results will be outlined. This includes a discussion on the manner in which a number of the sources of instability that occur during synchrotron mu-XRF experiments can be eliminated. The procedure is employed to measure the degree of micro-heterogeneity of several existing reference materials and to evaluate their suitability for calibration of trace-level micro-anal ytical methods. After analyzing the micro-heterogeneity of elements in thes e different reference materials, a minimum sampling mass for homogeneous me asurements is calculated. (C) 2000 Elsevier Science B.V. All rights reserve d.