X-rays released by the sample are used to determine which elements are present and their concentrations. This XRF can measure all the elements in the periodic table from Oxygen upwards and is the preferred method for measuring major elements. Detection limits range from one part per million for heavy elements to 1000 ppm for Oxygen. This technique is usually applied to solid samples, although it is possible to measure powders or even liquids.
High precision analyses requires careful calibration and sample preparation.
A semi-quantitative scan can be used to measure all the elements in the sample. Using this scan, analyses can be obtained in the absence of any calibration standards, or with samples which are too small, or not powdered, although the latter must fit into the 50 mm diameter sample holders. Analyses times are of the order of minutes, and 17 minutes for the semi-quantitative scan. The main advantages of XRF are relatively simple sample preparation, rapid analyses, the ability to re-analyses samples many times, and with uniform predictable sensitivity. The XRF used by the Geology department is a Philips machine, model number 2404.