Combustion of organic samples by infrared furnace for carbon isotope analysis
Abstract:
An apparatus for converting organic samples to carbon dioxide is described. It is especially designed to determine stable carbon isotope ratio of field samples. Unlike previous apparatus of similar configuration, a "Craig-line," it is free from the deposition of charred carbon on the line that results from an incomplete conversion. It includes an infrared furnace that heats both a CuO column and a sample tube. A removable, stainless-steel tube is present around the heated area, and this particular configuration makes it possible to begin every combustion procedure from room temperature, and consequently, to achieve a complete evacuation of air from the line even for heat-labile samples. The apparatus also includes a column that eliminates contaminating oxides such as nitrous oxide. The time necessary to process a sample is less than 30 min, and the precision of the carbon isotope measurement is comparable with that of "Craig-line." The coefficient of variation of carbon content determinations was no more than a few percents for most samples examined. An incidental finding was made that an isotopic fractionation of uric acid occurred during its preparation from penguin excreta by a high-performance liquid chromatography.
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