Selecting Standards to Optimize Electron Microprobe Analysis

Abstract Quantitative analysis with the electron microprobe analyzer (EMPA) has yielded more accurate results over time as a result of improvements in ZAF and other correction routines, mass absorption coefficients, synthetic pseudocrystals for ultralight elements, computers, software programs, backscattered electron (BSE) and energy dispersive (EDS) X-ray detectors. Consequently, many geoscientists view EMPA as routine, and details of procedures, standards, and operating conditions are seldom provided in current publications. However, in overseeing a facility with many users, we have learned that acceptable analytical data are sometimes difficult to obtain even with established analytical procedures and a choice of several hundred standards. After novice users have mastered the routines of sample polishing, cleaning, coating, handling and machine focus, their choice of nonoptimal standards often prevents them from obtaining the most accurate results possible. Optimal analysis for geological problems requires choosing appropriate standards, selection of optimal operating conditions, as well as consideration of the possibility of omitted elements, peak and background overlaps, matrix absorption effects, beam damage and elemental migration, reintegration of heterogeneous materials, fluorescence effects, and variations in the oxidation state of iron.