Analytical Lab Development through
Undergraduate Chemical Education Research
ABOUT
HOW IT WORKS
Instrument - Total Nitrogen Analyzer
The instrument used for this lab is the TOC/TN analyzer made by Shimadzu; allowing for the analysis of Total Organic Carbon (TOC) as well as Total Nitrogen (TN). For these experiments, we wil just be focusing on the TN measures the total nitrogen present using a chemiluminescence detector. This is the only instrument that measures TN; others measure the individual species in the water.
The total nitrogen analyzer consists of four main parts: an injector, combustion tube, dehumidifier and chemiluminescence detector.
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Injector
A needle pierces the septa of the vial and draws up a pre-selected amount of sample.
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Combustion tube
The sample goes through the combustion tube that is at a temperature of 720°C, this high temperature allows for the total nitrogen in the sample to decomposed nitric oxide (NO).
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Dehumidifier
Once the total nitrogen is decomposed to nitric oxide, it must be then cooled and dehumidified to get rid of any excess water.
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Chemiluminescence detector
Like any detector the purpose is to detect the amount of compound that is present in a sample, a chemiluminescence detector does this as a result of a chemical reaction that produces an emission of light and this is what is detected and the instrument reads out. Ozone (O3) and NO chemically react and produce NO2 in the excited state (*), when NO2* reverts back to the ground state, light energy is produced and is detected by the instrument. The chemical reaction is below:
NO + O3 -> NO2* + O2 + hv