ASTM D6069 Test Method for Trace Nitrogen in Aromatic Hydrocarbons
ASTM D6069 Standard Test Method for Trace Nitrogen in Aromatic Hydrocarbons by Oxidative Combustion and Reduced Pressure Chemiluminescence Detection
4. Summary of Test Method
4.1 A specimen is introduced into a gas stream, at a controlled rate, and carried into a high temperature furnace (>900°C) where an excess of oxygen is added. Pyrolysis converts organic material in the specimen to carbon dioxide and water. Organic nitrogen and inorganic nitrogen compounds, present in the specimen, are converted to nitric oxide (NO). Nitric oxide reacts with ozone in the detector producing nitrogen dioxide molecules in an excited state. As the excited nitrogen dioxide molecules relax to ground state, light is emitted. This light is detected by a photomultiplier tube with the resulting signal proportional to the concentration of nitrogen in the sample. Operating the detector at a reduced pressure, lowers the probability of the excited nitrogen dioxide molecules colliding with other molecules before they undergo chemiluminescence. Thus, reduced pressure provides improved sensitivity and lower noise.
5. Significance and Use
5.1 This method has been prepared to detect and quantitate nitrogen-containing compounds such as N-formylmorpholine (4-formylmorpholine, Chemical Abstract Service numbers (CAS) No. 250-37-6) or 1-methyl-2-pyrrolidinone (NMP) (CAS) No. 872-50-42 at a concentration of 1.0 mgN/kg or less in aromatic hydrocarbons used or produced in manufacturing processes. These nitrogen-containing compounds are undesirable in the finished aromatic products and may be the result of the aromatic extraction process. This test method may be used in setting specifications for determining the total nitrogen content in aromatic hydrocarbons.
NOTE 1 - Virtually all organic and inorganic nitrogen compounds will be detected by this technique.
5.2 This technique will not detect diatomic nitrogen and it will produce an attenuated response when analyzing compounds (that is, s-triazine and azo compounds, etc.) that form nitrogen gas (N2) when decomposed.
5.3 This test method requires the use of reduced pressure at the detector. Loss of vacuum or pressure fluctuations impact the sensitivity of the detector and the ability to determine nitrogen concentrations less than 1 mg/kg.
6. Interferences
6.1 Chlorides, bromides, and iodides can interfere if any one or all of these elements are present in a sample in concentrations greater than 10 % by total weight of halogen in the sample.
6.2 Moisture produced during the combustion step can interfere if not removed prior to the detector cell.
