General Description

Our instruments determine organic carbon, hydrogen, and nitrogen by means of high-temperature (1000C) combustion (Dumas method) of microgram to milligram size samples in an oxygen-enriched helium atmosphere. The combustion products CO2, NOX (reduced to N2), and H2O  are separated by means of sequential, selective chemical traps, and measured with three pairs of high-precision thermal conductivity detectors. Interfering gases of sulfur, halogens, and phosphorus are removed in the combustion reactor using the appropriate solid reagents. Samples, which have been precisely weighed into small tin capsules, placed in protective nickel sleeves for the analysis. Analysis results are reported in weight percent of the element.

In addition to solid sample materials, particulate organic matter trapped on glass fiber filters can be analyzed. Filters are not weighed, but are placed directly into nickel sleeves for analysis. (A nickel sleeve can accommodate a filter of up to 25mm diameter.) Results are reported in absolute micrograms of the element on the filter.

The control software for the instruments is capable of having the autosampler deposit two sample capsules on the ladle for a single analysis. In this mode, called 'double-drop,' larger total sample weights (for low organic-content materials) and larger diameter glass fiber filters (up to 47mm) can be analyzed.