Sum Peaks in a Total Reflection X‐Ray Fluorescence Spectrum of the Dry Residue of a Solution Sample Containing Ca

ABSTRACT In this study, sum peaks related to the Ca Kα line (3.69 keV) were observed in total reflection X‐ray fluorescence spectra of dry residues of a solution sample containing a large amount of Ca, which were measured with a silicon drift detector. When dry residues containing 1 μg of Ca were measured, a peak that would be the sum peak of the Si Kα line (1.74 keV) originating from sample holders and the Ca Kα line appeared at around 5.4 keV in each spectrum. Net intensities of the sum peak, which can overlap with the Cr Kα line (5.41 keV), were comparable to that of the Cr Kα line from the dry residue containing 200 pg of Cr. The sum peak can be misinterpreted as the Cr Kα line, and this misinterpretation leads to a false decision that a trace amount of Cr is contained in the dry residue of a water sample that does not actually contain Cr.