Determination of Nitrogen in Plastics

Importance of the topic

The determination of nitrogen content in plastics is critical for controlling product quality and material properties across packaging, automotive, medical devices and insulation sectors. Accurate nitrogen analysis supports compliance with performance specifications, helps optimize formulations and ensures material consistency during manufacturing processes.

Objectives and article overview

This application note presents an automated Dumas combustion method for rapid and precise determination of total nitrogen in plastic samples using the LECO FP928. It aims to replace time‐consuming Kjeldahl digestion with a five‐minute, reagent‐free analysis suited for routine quality control in the plastics industry.

Methodology

Sample masses of approximately 1.0 g are introduced into ceramic or nickel boats. After adding water to minimize sooting, samples undergo high‐temperature combustion (800 °C) in a pure oxygen atmosphere. Combustion gases are dried via a thermoelectric cooler, reduced in a copper‐packed tube to convert NOx to N₂, and a defined aliquot is carried by an inert gas (preferably helium) through a thermal conductivity detector. Calibration, blanking and drift correction procedures ensure accuracy at low ppm levels.

Used instrumentation

• LECO FP928 macro nitrogen determinator with horizontal ceramic furnace
• Ceramic combustion boats (528-203) and nickel liners (502-343 or 625-505-430)
• Pure oxygen supply for combustion and helium carrier gas
• Thermoelectric cooler for moisture removal
• Reduction tube packed with copper
• Automated autosampler and analytical balance

Main results and discussion

Typical analyses of polypropylene, high-density polyethylene and polyethylene terephthalate yielded average nitrogen contents of 0.019 %, 0.011 % and 0.014 %, respectively, with standard deviations below 0.004 %. The method demonstrates high sensitivity and precision, particularly when using a 10 cm³ aliquot loop and helium carrier gas. Careful control of sample mass, water addition and routine maintenance (filter tube replacement) minimizes sooting and ensures reliable long-term performance.

Benefits and practical applications

• Rapid analysis (~5 minutes) supports high sample throughput
• No hazardous chemicals or lengthy sample digestion required
• Low detection limits suitable for trace nitrogen in polymers
• Automated operation simplifies routine quality control
• Applicable to a wide range of plastic matrices

Future trends and possibilities

Advances in detector design and data processing may further enhance sensitivity and reduce maintenance. Integration with inline process analyzers could enable real-time monitoring of nitrogen levels in manufacturing lines. Potential extensions include adaptation to halogenated polymers, microplastic characterization and coupling with chemometric tools for formulation optimization.

Conclusion

The LECO FP928 Dumas combustion method offers a fast, accurate and solvent-free solution for total nitrogen determination in plastics. Its automation, low detection limits and minimal sample preparation make it an effective tool for routine quality control in a variety of polymer industries.

References

LECO Corporation, Application Note – Determination of Nitrogen in Plastics, Form No. 203-821-669, April 2023