Faster Measurement of Minerals in Milk Powders: Comparison of a High Power Wavelength Dispersive XRF System with ICP-AES and Potentiometry Reference Methods

A simple and quick (less than 5 min/pellet) method for the quantification of a series of macroelements (Na, Mg, P, Cl, K, and Ca) and trace elements (Fe, Cu and Zn) by wavelength dispersive X-ray fluorescence (WDXRF) has been established and validated for fortified milk powders, from a single production site. The calibration set of 23 samples was selected to uniformly cover the concentration ranges of each element. The validation set was composed of 32 samples. By using a high power WDXRF instrument, a counting time as short as 20 s for most of the analytes can be used to considerably decrease analysis time. Reference values obtained by inductively coupled plasma-atomic emission spectroscopy and by potentiometry for chloride were used to calibrate the WDXRF system. Subsequently, the WDXRF results were evaluated against those obtained from the reference methods. The results show good performance of the WDXRF method for routine analysis of milk powders including copper at low levels (<10 mg/kg). All the calibrations gave R2 > 0.98, while all validation work has been done using three replicates of each sample; the results have additionally been reassessed to check that only two replicates per sample would not lead to significant differences in terms of quality of data and could be considered for routine analysis to further decrease analysis time.