Three-dimensional elemental imaging by means of synchrotron radiation micro-XRF: developments and applications in environmental chemistry

Abstract

The most brilliant sources of hard X-rays available for scientists today are provided by synchrotron radiation (SR) sources within electron or positron storage rings. These storage rings, or particle accelerators, were originally built for high-energy particle physics experiments, and the emission of synchrotron radiation, generated by the acceleration of relativistic charged particles in strong magnetic fields, was considered as an undesirable sideeffect. The unique characteristics of SR (extremely high brightness/intensity, natural collimation, polarization, energy tunability, and pulsed time structure), however, were quickly recognized to be very attractive for a large number of scientific disciplines, including X-ray spectroscopic applications with unsurpassed sensitivity and spatial resolution. The original use of synchrotron radiation in the socalled parasitic mode in the case of first-generation synchrotrons, initiated a rapid evolution towards secondand third-generation SR sources which have been optimized specifically for the production of synchrotron radiation of exceptional brilliance. Owing to the rapid development of synchrotron sources, associated microfocusing optical elements and the increasing availability of sophisticated X-ray detectors, scanning micro X-ray fluorescence (micro-XRF) techniques have become extremely powerful tools for twoand three-dimensional (2D/3D), non-destructive elemental analysis with exceptional sensitivity. A variety of scanning XRF techniques are currently available, such as conventional or dynamic microXRF scanning (2D), micro-XRF computed tomography (2D/ 3D), and confocal micro-XRF (2D/3D) [1]. When using synchrotron sources to produce the exciting microbeam, taking advantage of the high intensity, potential monochromaticity/tunability, and high degree of linear polarisation in the storage ring plane, these techniques offer the possibility to obtain quantitative information on the elemental distributions within the sample volume with trace level detection limits and on a (sub-)microscopic scale [2, 3]. X-ray microprobes installed at the most advanced third-generation SR sources, such as the European Synchrotron Radiation Facility (ESRF) in Grenoble, offer absolute detection limits (DLs) below 10 ag for the most efficiently excited transition elements with a potential lateral resolution level better than 50 nm [4, 5]. An exciting direction in the development of nondestructive elemental imaging methods is represented by the combination of synchrotron-based scanning microAnal Bioanal Chem (2008) 390:267–271 DOI 10.1007/s00216-007-1694-0