XRFS and PIXE: Are they complementary or competitive techniques?: A critical comparison

Abstract

The advantages and disadvantages of X-ray fluorescence spectrometry (XRFS) as a modern, routine instrumental technique for major, minor and trace element analysis of a wide variety of sample types are discussed. The instrumentation used in the technique is considered and recent developments and improvements summarized. Major differences between XRFS and PIXE (proton excitation only), such as excitation characteristics, background distribution, analytical volume, lower limits of detection and types of sample analysed, are critically examined and compared. It is concluded that XRFS is the better technique for the determination of elements with low energy lines, especially in the range 1–4 keV (Na through Ca) and when bulk or thick samples must be analysed. PIXE is best applied to the analysis of thin samples when limited amounts of sample are available, when analysis of only the surface layers is required and when low detection limits are necessary for elements with atomic numbers close to 40 and 80. One of the major problems facing PIXE analysis of thick samples is the extremely small analytical volume. Very careful sample preparation and homogenization is essential if the sampling error is not to be the limiting factor on the accuracy of the analysis. Total reflection XRFS is certain to become a strong competitor to PIXE analysis for the determination of trace elements in biological samples, solutions and natural waters. XRFS data for a number of trace elements in coals and rocks are compared and shown to be in good agreement with instrumental neutron activation and mass spectrometric isotope dilution data on the same samples.