Determination of Nitrogen/Protein in Feeds, Grains, and Pet Food

Significance of the Topic

The accurate measurement of protein in animal feeds, grains, and pet food is critical for nutritional labeling, feed formulation, and economic value determination. A reliable analytical approach ensures product quality and compliance with regulatory standards.

Objectives and Study Overview

This application note details the use of the LECO FP828 nitrogen/protein determinator under Dumas combustion conditions. The study aims to evaluate method performance across various sample matrices, compare carrier gases, and validate compliance with AOAC 990.03.

Methodology and Instrumentation

The Dumas combustion technique employed a vertical quartz furnace under pure oxygen. Moisture removal was achieved via a thermoelectric cooler before gas equilibration in a ballast and analysis in a thermal conductivity detector (TCD). Both helium and argon were examined as carrier gases to assess sensitivity and precision. Key method parameters included a furnace temperature of 950 °C, afterburner at 850 °C, and a 3 cm3 dose loop.

Used Instrumentation

• Instrument model: LECO FP828 nitrogen/protein determinator
• Accessories: tin foil cups (502-397), spatula (501-614)
• Reference materials: LCRM®, LRM®, NIST standard reference materials

Main Results and Discussion

Analysis of standard reference materials and various feeds (dry cat food, hay, corn silage, distillers grains, feed mix, corn grain) yielded consistent nitrogen and protein values. Helium provided higher detector sensitivity at low nitrogen concentrations, though both gases yielded comparable average protein content (±0.1%). Moisture corrections applied using AOAC 930.15 ensured dry-basis reporting. Results demonstrated excellent reproducibility with standard deviations below 0.05% N for most matrices.

Benefits and Practical Applications

• Rapid, high-throughput protein analysis without hazardous chemicals
• Compliance with established AOAC methods
• Broad applicability to diverse feed matrices
• Cost-effective calibration using single-standard Dumas approach

Future Trends and Potential Applications

Advancements may include automated sample handling, integration with laboratory information management systems (LIMS), alternative gas carriers or detectors for enhanced sensitivity, and real-time in-line monitoring in feed production.

Conclusion

The LECO FP828 offers a robust Dumas combustion solution for precise nitrogen/protein determination in various animal feed and grain samples. Its performance meets regulatory requirements and supports efficient feed quality control.

References

• Association of Official Analytical Chemists (AOAC). (1990). AOAC 990.03 Protein (Crude) in Animal Feed, Combustion Method.
• United States Department of Agriculture. (1950). Circular No. 183, Protein Factors for Food Minerals and Feedstuffs.