An Automatic X-Ray Analytical Instrument for the Chemical Laboratory

Abstract

Although isotope excited non-dispersive X-ray analysis has shown considerable promise for use in portable instruments and in on-line control applications, its use as a general analytical tool in the chemical laboratory has not developed as well as expected. Much of this is thought to be due to lack of flexibility in the instruments available and to difficulties with their use by unskilled operators. Wide element coverage is essential and many analytical problems arise at the light element end of the periodic table. While developing on-line techniques for light elements it was found that a measuring head using a very compact source-sample-detector geometry was well suited to a number of routine analytical laboratory problems, and enabled high precision to be obtained with minimum sample preparation for rapid single element analysis. Sensitivities in a light matrix from 100 p.p.m. for silicon to 10 p.p.m. for heavy elements were attainable. An instrument specifically for chemical laboratory use was therefore designed to accept solid, liquid and powder samples for single element analysis of silicon and all heavier elements. The instrument can give direct numerical readout of concentration and achieves high stability and precision. In its basic form it is equipped with a range of isotope excitation sources but will also accept a small X-ray tube which has been specially developed for it to provide higher sensitivity and precision. The measuring head may be removed for remote use, and multiple sample changing facilities with printout of results can be added, permitting unattended automatic routine analysis.