Environmental Solutions

ASTM D8083-16 for Total Nitrogen couples the Shimadzu TOC-L with a chemiluminescent nitrogen detector. The combustion tube is packed with a catalyst (platinum on an alumna support) and capped with a small amount of ceramic fiber. The combustion tube is assembled in a furnace and heated to 720°C. Zero carbon air is used as a carrier gas and as a supply of oxygen to the ozone generator of the nitrogen detector. The sample stream passes through a thermoelectric cooler immediately after exiting the combustion tube.

Sample nitrogen introduced into the combustion tube converts to nitrogen monoxide (reactions 1 and 2). Nitrogen gas in the carrier gas (air) does not interfere. The carrier gas containing the nitrogen monoxide (NO) is cooled and dehumidified in the thermoelectric cooler. The cooled gas then enters the chemiluminescence analyzer where the NO reacts with ozone (O3) and converts to a combination of nitrous oxide (NO2) and excited nitrous oxide (NO2*) (reactions 3 and 4). As the NO2* returns to the ground state it emits radiation, which is measured photo-electrically (reaction 5). The detector signal generates a peak that is proportional to the nitrogen concentration in the sample.