The organic carbon fraction in sediments is important because it serves as a binding site for contaminant metals. The abundance of organic carbon controls many diagenic processes. Normalising contaminant data by the percentage organic carbon allows for the distinction of specific anthropogenic sources.
Technical Note 230 describes how sediment samples are placed in acid to dissolve the inorganic material and then filtered. The filters are then analysed using an Exeter Analytical Model CE440 CHN elemental analyser. The optimised Model CE440 methodology uses a combustion method to convert the sample elements in the sediment samples to simple gases (CO2, H2O and N2). Elements such as halogens and sulphur are removed by scrubbing agents. The resultant gases are homogenised and controlled under exact pressure, temperature and volume conditions. The homogenised gases are then passed through a known sample volume. This volume of sample gas products is then passed through a series of steady state detectors with CO2 and H2O traps placed between first two detectors this enables accurate quantification of the three elements of interest (carbon, hydrogen and nitrogen).
The Model CE440 is a static combustion system, with a unique horizontal furnace design, which enables easy removal of filter and sample ash between each analysis. Consequently one combustion tube will analyse in excess of 1000 samples without the need for removal and cleaning. In addition the Model CE440 provides the capacity to process filters up to 47 mm in diameter in one analytical cycle. By comparison other elemental analysers, employing vertical furnace designs, need cleaning after as little as 20 samples and larger filters have to be sub sampled several times and then corrective calculations made to enable analysis.
Effectively eliminating troublesome residue build-up the gas flow characteristics of the Model CE440 analyser are superior to other elemental analysers thereby providing longer-term calibration stability as well as enhanced accuracy and precision for measured sample data.
As the Model CE440 also provides complete control over combustion parameters it is able to reproducibly achieve 100% combustion with the widest range of sediment samples.
For sediment samples with low levels of Nitrogen in the 0.1-0.2% range, new Nitrogen analysis software for the Model CE440 uniquely enables accurate measurement at these levels with a high degree of accuracy.
For further information on direct determination of organic carbon in sediment samples please contact Exeter Analytical.