Nitrogen/Protein in Feeds, Grains, and Oil Seeds (TruMac N)

Significance of the Topic

Accurate and precise protein measurement is essential for assessing the nutritional quality and economic value of feeds, grains, and oil seeds. Determining nitrogen as a proxy for protein underlies critical decisions in animal nutrition, feed formulation, and quality control in agricultural and food industries.

Objectives and Study Overview

The study presents the LECO TruMac® N macro combustion nitrogen/protein analyzer and evaluates its performance for feed, grain, and oil seed samples. Key goals include demonstrating macro sample capability (~1 g), rapid analysis, low cost per analysis, and comparison of carrier gases (helium vs. argon) and gas collection loops (3 cc vs. 10 cc).

Methodology and Instrumentation

Samples are ground to <0.5 mm for uniformity. Approximately 0.5–1 g is combusted in a ceramic horizontal furnace at 1100 °C under pure oxygen. A thermoelectric cooler removes moisture without reagents. Combustion gas is collected in either a 3 cc or 10 cc aliquot loop. Nitrogen oxides are scrubbed and converted to N₂ with minimal reagent use. A thermal conductivity detector measures N₂ relative to a carrier gas (helium or argon).

Instrumentation Used

• TruMac® N macro combustion nitrogen/protein analyzer
• Ceramic horizontal furnace (1100 °C) and pure oxygen environment
• Thermoelectric cooler (5 °C) for moisture removal
• Thermal conductivity detector with helium or argon carrier gas
• 3 cc and 10 cc combustion gas aliquot loops

Main Results and Discussion

Typical analyses of pet food and grain samples produced consistent nitrogen (%N) and protein values across gas loops and carrier gases. Helium/3 cc gave %N precision (s) ~0.02 and protein precision ~0.1; helium/10 cc and argon/10 cc showed similar averages with slightly higher variability (s up to 0.04 %N, 0.3 % protein). All configurations delivered reproducible results within 0.1–0.3 % protein. Helium offered higher sensitivity at low nitrogen levels, while argon provided comparable practical performance amid helium supply limitations.

Benefits and Practical Applications

• Macro sample capability (~1 g) ideal for heterogeneous feeds and seeds
• Rapid cycle times: 35 s (helium) to 55 s (argon) per analysis
• Reduced reagent consumption and low cost per analysis
• Flexibility to operate with helium or more accessible argon carrier gas
• Single-point calibration using EDTA simplifies routine QA/QC

Future Trends and Potential Applications

Advances may include coupling with automated sampling systems, alternative calibration strategies (multi-point or matrix-matched standards), integration into high-throughput QA/QC workflows, and exploration of novel carrier gases. Further miniaturization and software enhancements could improve data processing and traceability in certification laboratories.

Conclusion

The LECO TruMac N delivers accurate, precise, and high-throughput nitrogen/protein analysis for feeds, grains, and oil seeds. Its macro combustion approach, choice of carrier gas, and reduced reagent requirements make it a robust solution for research and routine industrial quality control.

Reference

• USDA Circular No. 183: Protein conversion factor (6.25)
• AOAC Official Method 990.03 and AOCS Ba 4f for sample preparation guidelines