DEVELOPMENT OF A STANDARD OPERATING PROCEDURE FOR QUANTITATIVE ANALYSIS USING CENTRAL WASHINGTON UNIVERSITY'S RIGAKU MINIFLEX 600 BENCHTOP X-RAY DIFFRACTOMETER

X-ray diffraction can be used to collect and analyze data to determine the phases present (qualitative analysis) and their abundance (quantitative analysis) in a multiphase sample. The goal of our project is to develop a standard operating procedure for sample preparation, data collection, and analysis to achieve results that are optimized for quantitative analysis of multiphase samples using the Rigaku MiniFlex 600 benchtop X-ray diffractometer (XRD). First, we determined the milling time necessary to reduce mineral samples’ particle size to a fine powder (~10-20 µm) without larger fragments that can cause incorrect quantitative results due to domination of the diffraction pattern. We used the Retch Mixer Mill MM 400 instrument for milling. We have found that the milling duration needed for 10 g of a sample, at a frequency of 30 Hz, varies considerably depending on mineral type. Biotite and muscovite took the shortest amount of time at 35 minutes. The plagioclase minerals took the longest at 70 minutes or more, with the longest duration being 110 minutes. The next part of the project is to determine the XRD operating conditions required to collect publishable results for quantitative XRD analysis. The main parameter tested is the duration of analysis. The measurement duration starts at 8 minutes (the speed is 10 degrees/minute) and increases to 3 hours and 20 minutes (0.4 degrees/minute). The peak-to-background ratio of the data varied within a small range (12.2-12.8), but increased for the last two measurement duration intervals (13.3 and 14.0). Comparing the anorthoclase spectra qualitatively: the peaks and background become smoother with increased measurement time. Smaller peaks also become more pronounced and more easily distinguishable from the background level with increased analysis time. While we have so far focused on individual mineral samples, these conditions will be evaluated further using both synthetic rock mixtures and real rocks. These multiphase samples will be used to determine the optimized analysis routine for XRD quantification.