The analyzer is an instrument designed for the simultaneous determination of total nitrogen and carbon in a wide range of organic and inorganic solid samples. A few examples of possible samples are: plant tissues, soils, fertilizers, paper products, feed, and some metals.
The analysis method is based on the complete and instantaneous oxidation of the sample by "flash combustion" which converts all organic and inorganic substances into combustion products (CO2 and NOx). The resulting combustion gases pass through a reduction furnace where the NOx compounds are converted to N2 gas, and are carried into the chromatographic column by helium carrier gas. The analyte gases are separated in the column and detected by the thermal conductivity detector which gives an output signal proportional to the concentration of the individual components of the mixture.
The sample to be analyzed is weighed into a tin container and loaded into the autosampler. The sample is then deposited into the combustion reactor which is maintained at 1020 degrees C. The sample and container are combusted in a temporarily enriched atmsophere of oxygen. Under these conditions even thermally resistant substances are completely oxidized. The mixture of combustion products (CO2, NOx, and H2O vapor) pass first through an oxidation catalyst (Pt and CuO) and then through a reduction reactor containing metallic copper at 650C. The excess of oxygen is removed and the nitrogen oxides are reduced to dinitrogen gas. The gasses then pass through a the magnesium perchlorate trap, which removes the water vapor. The helium stream then flows through a chromatographic column which separates the nitrogen and carbon. From there the gases flow through a thermal conductivity detector which generates an electrical signal proportional to the concentrations. Analyzing a standard of known composition under the same conditions makes it possible to calibrate the instrument and quantify the content of nitrogen and carbon in a unknown sample.
