Double-Plate Sample Carrier for a Simple Total Reflection X-Ray Fluorescence Analyser

Abstract

A simple total reflection x-ray fluorescence (TXRF) analyser was constructed using an original double-plate sample carrier. The carrier consists of two glass microscope slides, one 25 mm longer than the other, which function simultaneously as both the collimator and the sample holder. Total reflection conditions are achieved in the space between the two plates, completely eliminating the need for precise sample positioning. Because the instrument consists of simple mechanical parts, it can be made in most laboratories using traditional XRF components (x-ray generator and energy-dispersive x-ray spectrometer) which are readily available. Despite the simplicity of the design, the instrument has essentially all of the capabilities of conventional TXRF machines: multi-element analysis (Cl to U), low limits of detection (pg) and a requirement for only very small volumes (μl) of sample. The detection limits which can be achieved using 50 μl samples depend on the quality of the plate surface. For example, using glass microscope slides for plates, the absolute detection limit for first series transition metals (Sc to Zn), Pb and Sr are of the order of 200 pg; this is adequate for a wide range of geological and environmental samples. The detection limits could be further improved by either (1) placing the sample carrier and detector head in a vacuum chamber, (2) by using monoenergetic excitation, because of the high efficiency of the double-plate collimator, or (3) by using highly polished quartz plates instead of glass for the sample carrier.