Determination of Nitrogen in Fertilizer (FP828)

Significance of the Topic

Nitrogen plays a central role in enzyme and protein synthesis in plants, directly influencing crop yield and quality. Accurate quantification of total nitrogen in fertilizers ensures proper nutrient management, supports agricultural productivity, and underpins regulatory compliance.

Objectives and Study Overview

This application note evaluates the performance of the LECO FP828 combustion nitrogen analyzer following AOAC 993.13 for various fertilizer types. Key goals include assessing precision, accuracy, and operational parameters using helium or argon carrier gas and two aliquot loop volumes.

Applied Instrumentation

• LECO FP828 vertical quartz furnace with pure oxygen combustion
• Thermoelectric moisture removal unit and ballast gas collection system
• Thermal conductivity detector with helium or argon carrier gas
• Aliquot loops: 10 cm3 for low nitrogen levels, 3 cm3 for extended reagent life
• Sample handling accessories: tin foil cups and capsules

Methodology

Samples (powder, granular, or liquid fertilizers) are weighed (0.05–1 g) into tin cups or capsules, mixed with sucrose when needed, and introduced into the FP828. Combustion occurs at 950 °C followed by afterburning at 850 °C. Moisture is removed and gases equilibrate in the ballast before aliquots are carried in helium or argon to the thermal conductivity cell. Calibration and drift correction use certified reference materials (e.g., NIST 913b Uric Acid).

Main Results and Discussion

Typical results for urea, ammonium sulfate, and potassium nitrate showed averages within 0.1% of theoretical nitrogen values and standard deviations below 0.1% with helium and 0.1–0.5% with argon. The 10 cm3 loop provided optimal precision at low nitrogen concentrations, while the 3 cm3 loop extended reagent life with minimal trade-off in accuracy. Detection down to 0.01–0.10% N was demonstrated with appropriate loop selection.

Advantages and Practical Applications

The method delivers rapid, reproducible total nitrogen analysis across diverse fertilizer matrices. High throughput and minimal sample preparation streamline quality control and batch certification. Flexible carrier gas options balance sensitivity and operating costs.

Future Trends and Opportunities

Advances may include integration with automated sample handlers, alternative inert gases to reduce costs, and coupling with complementary detectors for multi-element analysis. Enhanced software algorithms could further improve drift compensation and data quality.

Conclusion

The LECO FP828 system offers robust, accurate nitrogen determination in fertilizers, supporting agricultural productivity and regulatory standards. Selection of carrier gas and aliquot volume allows tailored performance for specific concentration ranges.

References

1. AOAC 993.13, Total Nitrogen in Fertilizers by Combustion Method
2. LECO 828 Series Operator’s Instruction Manual
3. Certified Reference Materials: LCRM®, LRM®, NIST standards