A. General Information
The analyzer is an instrument designed for the simultaneous determination of total nitrogen and carbon in a wide range of organic and inorganic samples. A few examples of possible samples are; plant tissues, soils, fertilizers, paper products, feed and some metals.
Please note that this instrument, due to the need to replace spent columns, will have down times that are for the most part unpredictable. Therefore, before signing up on the calendar, please contact Doug to determine the current state of the EA.
B. Theory of Elemental Analysis
The original 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. The resulting combustion gases pass through a reduction furnace and are swept into the chromatographic column by the carrier gas which is helium. The 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 results are comparable to those obtained by traditional methods, such as Kjeldahl and Dumas, but it offers faster analysis time with greater reproducibility and accuracy. An extra benefit of the flash combustion method is that no hazardous waste is created other than the spent columns that can be used for hundreds of samples.
C. Theory of Operation
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 melt and the tin promotes a violent reaction in a temporarily enriched atmsophere of oxygen. Under these conditions even thermally resistant substances are completely oxidized.The mixture of combustion products pass first through an oxidation catalyst of chromium trioxide in the reaction/combustion tube. The combustion products, those of interest being CO2, N2 and NOx, along with some water, then pass through a second tube known as the reduction reactor. It contains metallic copper kept at 650C. The excess of oxygen is removed and at this temperature the nitrogen oxides are reduced to elemental nitrogen, which together with CO2 and water pass to the magnesium perchlorate tube which removes the water. The helium stream then flows through a chromatographic column separating the nitrogen and carbon. From there the gases flow through the thermal conductivity detector which generates an electrical signal proportioal 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.
