Determination of Nitrogen in Fertilizer

Importance of the Topic

Accurate determination of nitrogen content in fertilizers is essential for optimizing crop yield, ensuring proper plant nutrition and maintaining soil health. Nitrogen is a critical macronutrient that influences enzyme and protein synthesis, directly affecting plant vigor and productivity. Consistent and precise nitrogen measurement supports fertilizer blending, quality assurance and regulatory compliance in agricultural production.

Objectives and Study Overview

This application note presents a robust analytical protocol for total nitrogen determination in various fertilizer types using the LECO CN928/FP928 macro combustion analyzer. The study aims to demonstrate method performance, describe optimal instrument settings and sample preparation procedures, and illustrate typical results across multiple fertilizer matrices.

Instrumentation Used

The method employs the LECO CN928/FP928 dual carbon and nitrogen/protein determinator featuring:

• Pure oxygen horizontal ceramic combustion furnace operating at 1350 °C
• Thermoelectric cooler for moisture removal from combustion gases
• Ballast reservoir and gas handling system with selectable 10 cm3 or 3 cm3 aliquot loops
• Thermal conductivity detector for N2 measurement using helium or argon carrier gas
• Accessories including ceramic combustion boats, nickel liners, crucible tongs and spatula

Methodology and Instrumentation

Sample preparation and analysis follow AOAC Official Method 993.13:

• Solid fertilizers: Grind to uniform consistency, weigh ~0.10 g, mix with ~0.4 g sucrose, load into ceramic boat
• Liquid fertilizers: Weigh 0.1–2.0 g sample into nickel boat liner within ceramic boat, no sucrose required
• Blank determination and multi-point calibration using NIST 913b Uric Acid or LECO Urea CRM
• Carrier gas selection: Helium for highest sensitivity, argon for alternative operation
• Instrument parameters: Furnace at 1350 °C, multiple purge and baseline cycles, selectable aliquot volumes

Main Results and Discussion

Typical performance data demonstrate excellent accuracy and precision across nitrogen concentrations:

• Urea, ammonium sulfate and potassium nitrate analyses yield recoveries within ±0.3% of theoretical N values
• Relative standard deviations (RSD) typically below 0.1% with helium and below 0.2% with argon
• Helium carrier gas provides superior sensitivity at low N levels compared to argon
• The 3 cm3 aliquot loop reduces reagent consumption by three-fold while maintaining comparable precision to the 10 cm3 loop

Benefits and Practical Applications

• High throughput and low cost per analysis for routine fertilizer quality control
• Wide dynamic range supports trace to high-level nitrogen determinations
• Simplified calibration and drift correction procedures enhance operational efficiency
• Compliance with regulatory standards and support for commercial fertilizer certification

Future Trends and Possibilities

Emerging developments may further enhance fertilizer nitrogen analysis:

• Automation of sample handling and data processing for increased laboratory throughput
• Integration of multi-element detection (C, N, S, O) for comprehensive nutrient profiling
• Adoption of greener carrier gas alternatives and advanced detector technologies
• Implementation of remote monitoring and AI-driven analytics for real-time process control

Conclusion

The LECO CN928/FP928 macro combustion method delivers accurate, precise and cost-effective total nitrogen analysis in diverse fertilizer matrices. The flexibility of carrier gas choice and aliquot volume, combined with streamlined calibration procedures, makes this approach ideal for quality assurance, regulatory compliance and research applications in agricultural chemistry.

Reference

• AOAC Official Method 993.13 Total Nitrogen in Fertilizers by Combustion
• LECO CN928/FP928 Operator's Instruction Manual
• NIST 913b Uric Acid and LECO Certified Reference Materials (LCRM, LRM)