Elemental C, H and N microanalysis of crushed rock and soil samples

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Abstract
A sensitive and reproducible method for elemental analysis of rock and soil samples has been developed using a modified Hewlett‐Packard 185 CHN analyzer. Samples are combusted in an inert He atmosphere (with and without catalyst) with a carefully controlled combustion time and temperature. Absolute mass calibration is available on samples of from 1–500 µg total CHN content. Analysis of chromatograms is made by both manual and computer techniques. Finely crushed rock (or dust) samples of from 50–100 mg may be analyzed for most forms of carbon content and for N and H with a high degree of technical reproducibility. Step‐wise calcination at 150 C and 550 C allows evaluation of adsorbed CO2, potential organic and amorphous carbon content. Although carbide carbon is partially recovered, essentially quantitative recovery of finely divided graphitic (and diamond) as well as amorphous, carbonate and all organic carbon may be obtained.