DIRECT MAJOR (C, O, N) AND MINOR ELEMENT ANALYSIS OF MACERALS BY ELECTRON-MICROPROBE

Recent advances in electron microprobe technology together with the de velopment of synthetic crystals has enabled development of techniques for direct light element (C, O, N) analysis of coal macerals. The anal ytical results are both accurate compared to ASTM methods and highly p recise, providing an opportunity to assess variation in maceral chemis try without the necessity of physical concentration. Utilizing a nicke l-carbon pseudocrystal (d = 9.5 nm) as an analyzing crystal, a 10 kV a ccelerating voltage and a 10 nA beam current yields the most reliable data and results in minimum sample damage. We used vitrinite isolated from an anthracite as the carbon standard, BN as the nitrogen standard , MgCO3 as the oxygen standard, and BaSO4 as the sulphur standard. Pro be-determined carbon and oxygen contents agree closely with those repo rted from ASTM analyses; some minor deviations are attributed to heter ogeneity of the vitrinite on the micrometer scale. The microprobe-dete rmined nitrogen content of our samples suggests that nitrogen is distr ibuted heterogeneously even within pure vitrinite. We cite examples of microprobe-determined chemical analysis of macerals contained within high-, medium-, and low-volatile bituminous coals to illustrate the ut ility of the method. These results demonstrate that the electron micro probe provides a rapid, accurate, and relatively inexpensive method fo r obtaining compositional data for both minor and major elements in co al without the necessity of and inherent problems associated with mech anical separation of macerals.