Direct determination of fluorine in high-purity water samples using vacuum sample chamber total reflection X-ray fluorescence spectrometry

Abstract

A simple total reflection X-ray fluorescence (TXRF) method for the direct determination of trace F levels in water samples has been developed. This method involves the deposition of 5 μL aliquots of samples and calibration solutions on Si-wafer supports and measurement of their TXRF spectra using a vacuum chamber TXRF spectrometer with ultrathin window detector. The small size of the deposited sample fixed at the center of the Si-wafer support provided reproducible geometry that ensured the measured F Kα intensity was the same for different specimens containing the same amount of F and varied in proportion to the amount of F. This approach resulted in a calibration plot of F Kα intensity against the amount of F on TXRF specimens prepared using the same aliquot volumes containing different F concentrations. Fluorine in sample solutions was determined using this calibration plot. This approach avoided use of an internal standard and, thereby, F loss due to the acidic nature of internal standards while preparing the TXRF specimens by drying sample solutions on TXRF supports. This approach allowed determination of the F amount in synthetic samples and simulated water samples with an average deviation in the TXRF results of 4.1% from expected values and an RSD of 5.1% (1σ) for the F amount at ppm and sub-ppm levels. The use of Si-wafer supports helped to prepare small sample spots on TXRF supports with reproducible geometry and better detection limits. This also avoided interference from the O Kα peak of quartz supports with the F Kα peak.