Residual analyte intensity exists in a spectrometer when, for example, the x-ray source is contaminated with the analyte. A blank specimen, identical to the sample but devoid of the analyte, may be used to determine this residual analyte intensity, and, thereby, allow quantification of that intensity due to analyte in the sample. It is generally considered that a single pure material could serve as a blank for many analytes in many matrices. In practice, at least for low average atomic number matrices such as glasses, the reflectivity of similar samples may differ substantially, rendering inaccurate this simple blank subtraction. In such cases a blank is needed for each sample, where the reflectivity of the blank is matched to that of the sample. In order to eliminate the need for generation of blanks to match each of the samples, a general method to quantify the net residual analyte intensity as a function of specimen reflectivity by measurement of two pure material blanks is proposed herein.