Electron Probe Microanalysis of Bromine in Minerals and Glasses with Correction for Spectral Interference from Aluminium, and Comparison with Microbeam Synchrotron X-Ray Fluorescence Spectrometry

摘要

The strong spectral interference between Br- and Al-induced X-ray lines hampers the utilisation of electron probe microanalysis (EPMA) for measuring Br mass fractions in Al-bearing minerals and glasses. Through measuring Br-free Al-bearing materials, we established an EPMA method to quantify the overlap from AlK alpha on BrL beta, which can be expressed as a linear function of the Al2O3 content. The count rate of the BrL beta peak signal was enhanced by high beam currents and long measurement times. Application of this EPMA method to Al- and Br-bearing materials, such as sodalite and scapolite, and to five experimental glasses yielded Br mass fractions (in the range of 250-4000 mu g g(-1)) that are consistent with those measured by microbeam synchrotron X-ray fluorescence (mu-SXRF) spectrometry. The EPMA method has an estimated detection limit of similar to 100-300 mu g g(-1). We propose that this method is useful for measuring Br mass fractions (hundreds to thousands of mu g g(-1)) in Al-bearing minerals and glasses, including those produced in Br-doped experiments. In addition, the natural marialitic scapolite (ON70) from Mpwapwa (Tanzania) containing homogeneously distributed high mass fractions of Br (2058 +/- 56 mu g g(-1)) and Cl (1.98 +/- 0.03% m/m) is an ideal reference material for future insitu analyses.