ASTM D4629: Detection of Total Nitrogen in Biodiesel

ASTM D4629 covers the determination of total Nitrogen in concentrations ranging from about 0.3 to 100 mg/kg in liquid petroleum products having a boiling point range of 50˚C to 400˚C and viscosities between 0.2 and 10 mm²/s at ambient temperature. The ASTM D4629 standard is the preferred method in many countries to detect and quantify total bounded nitrogen containing compounds in the various type of automotive fuels such as blended gasolines, diesel and synthetic oils. Nitrogen compounds can have detrimental effects on many environmental and industrial processes and are undesirable in finished products. This supports the need and importance to monitor trace level nitrogen concentration of various type of automotive fuels and related products. This application note shows the total bounded Nitrogen analysis performance of a set of liquid hydrocarbon samples, by the EST NEXIS Total Nitrogen analyzer. 

A liquid fuel sample is directly injected, automatically by the liquid auto sampler, AS/120 model, into a pre-heated injection port connected to a dual zone high temperature combustion tube where the nitrogen containing components are vaporized and combusted. The released nitrogen is oxidized to nitrogen oxide (NO) in an oxygen rich atmosphere.  A stream of inert gas (helium or argon) takes the reaction products, after removal of the produced water vapor by an effective membrane dryer, into the reaction chamber. The NO is swept to the detector, where it meets a stream of ozone to form NO2 in an excited electronic state: 

NO + O3 NO2* + O2…