| Abstract |
RationaleGas chromatography-combustion-isotope ratio mass spectrometry (GC/C/IRMS) is widely used for compound-specific carbon isotopic analysis. However, current isotopic analysis systems utilize the GC IsoLink combustion reactor, and independent reduction furnaces are not implemented. Therefore, whether this limitation in furnace use affects the precision of compound-specific carbon isotopic analysis needs to be evaluated. MethodsWe attempted to add a separate reduction furnace to the GC IsoLink interface and compared the delta C-13 values of n-alkanes (including C and H elements), fatty acid methyl ester (including C, H, and O elements), caffeine (USGS61 and USGS62, including C, H, O, and N elements), and 9-ethylcarbazole (including C, H, and N elements) before and after the addition of the reduction furnace using the GC IsoLink combustion reactor. ResultsFor n-alkanes and fatty acid methyl esters, the delta C-13 differences between the measured values and their standard values were basically falling within 0.5 parts per thousand whether or not an independent reduction furnace was added. However, for the nitrogen-containing compounds (caffeine and 9-ethylcarbazole), the delta C-13 differences between the measured values and their standard values were much larger without an independent reduction furnace (1.0-3.71 parts per thousand for USGS61, 1.78-2.19 parts per thousand for USGS62, and 0.39-1.13 parts per thousand for 9-ethylcarbazole) than with a reduction furnace (-0.31-0.68 parts per thousand for USGS61, -0.44-0.06 parts per thousand for USGS62, and -0.04-0.25 parts per thousand for 9-ethylcarbazole). ConclusionsThe addition of an independent reduction furnace had no significant effect on the delta C-13 of n-alkanes and fatty acid methyl esters, but it had a significant effect on the delta C-13 of nitrogen-containing compounds. It is suggested that GC IsoLink needs an independent reduction furnace to effectively eliminate the interference of NOx on CO2 isotopic determination to improve the accuracy of delta C-13 for nitrogen-containing compounds. |
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