The Carlo-Erba NA 1500 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.
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.
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.
