In the X-ray fluorescence analysis of homogeneous specimens, the correlation between the characteristic line intensity of an analyte element and the concentration of that element, is typically non-linear over wide concentration ranges, due to interelement effects between the analyte element and other elements making up the specimen matrix. Although in many cases limiting the analyte concentration range may allow the use of linear calibration curves based on type-standardisation, it is usually more desirable to work with general purpose calibration schemes which are applicable to a variety of matrix types over wide concentration ranges.