DETERMINATION OF ORGANIC-CARBON AND NITROGEN IN MARINE-SEDIMENTS USING THE CARLO-ERBA-NA-1500 ANALYZER

A technique is described for the determination of organic carbon and nitrogen in small samples (5 mg) of marine sediments that optimizes the analytical capabilities of the Carlo Erba NA-1500 Elemental Analyzer. This instrument analyses total carbon, nitrogen and sulfur in solid samples by flash combustion. Organic and inorganic forms of carbon are differentiated by sample manipulation prior to analysis without loss of nitrogen. Organic carbon is determined after removing carbonate carbon by acidification with sulfurous acid in situ within aluminum sample cups, thus eliminating loss of acid-soluble organic carbon during carbonate dissolution, or the necessity of determining organic carbon by "difference-on-combustion". Excess acid is volatized as SO2 and H2O upon drying, eliminating the dual problems of retention of waters-of-hydration of calcium salts and "excess" acid. The procedure provides rapid and rouitine analyses of marine sediments, yielding a relative precision of ±0.3% of the measured value for organic carbon and ±1.6% for nitrogen, and blank levels 0.31 ± 0.085 μg-carbon and 0 μg-nitrogen. Conservatively estimated absolute and relative detection limits are 0.62 μg-carbon (2 times mean blank value) and 0.01% carbon, respectively. © 1990.