Analysis of Sulfamic Acid in Fertilizers Using LC/MS (LCMS-2020)

Importance of the Topic

The accurate determination of sulfamic acid in fertilizers is critical because excessive levels can inhibit plant growth. Regulatory limits, such as those under the Japanese Fertilizers Regulation Act, require reliable analytical methods. Traditional ion chromatography can struggle with complex fertilizer matrices rich in organic matter, leading to poor peak separation and potential quantification errors.

Objectives and Study Overview

This study aimed to develop and validate a liquid chromatography–mass spectrometry (LC/MS) method capable of selectively detecting and quantifying sulfamic acid in fertilizers, including byproduct compound fertilizers with high organic content. The goal was to achieve sensitive, accurate results while minimizing sample pretreatment and matrix interferences.

Methodology and Used Instrumentation

Sample preparation followed standard fertilizer testing procedures: 1 g of fertilizer was extracted with 100 mL water, diluted 100-fold, and filtered. Spike and recovery tests used 0.5 mL of 100 mg/L standard to reach a measurement concentration of 0.005 mg/L.

• Instrument: Shimadzu LCMS-2020 single quadrupole mass spectrometer (ESI negative mode)
• Column: Phenomenex Luna HILIC (100 mm × 2.0 mm I.D., 5 μm)
• Mobile phase: Acetonitrile / 100 mmol/L ammonium formate + formic acid (pH 3.2) = 90:10 (v/v)
• Flow rate: 0.2 mL/min; Column temperature: 40 °C; Injection volume: 1 μL
• MS conditions: Probe voltage –3.5 kV; DL temp 250 °C; Block heater temp 400 °C; Nebulizing gas 1.5 L/min; Drying gas 15 L/min
• Detection: Selected ion monitoring (SIM) at m/z 95.9 (deprotonated sulfamic acid)

Main Results and Discussion

Calibration over 0.001–0.1 mg/L showed excellent linearity (R² > 0.999). At 0.001 mg/L, area reproducibility was 2.72% RSD. Retention time averaged 4.228 min (0.336% RSD). In byproduct fertilizer samples, no interfering peaks were observed at the sulfamic acid retention time. Spike recovery averaged 101% over five replicates, demonstrating high accuracy and precision.

Benefits and Practical Applications

The LC/MS approach offers superior selectivity and sensitivity compared to conventional ion chromatography, especially in complex matrices. The simplified workflow—water extraction, dilution, and filtration—reduces sample preparation time and minimizes potential losses. This method supports routine quality control and regulatory compliance in fertilizer production and inspection laboratories.

Future Trends and Applications

• Integration of high-resolution mass spectrometry for even greater specificity and identification of related impurities.
• Automation and on-line sample preparation to increase throughput in industrial settings.
• Miniaturization and portable LC/MS systems for field-based fertilizer analysis.
• Application of this approach to other analytes of regulatory interest in agricultural products.

Conclusion

The developed LC/MS method provides a robust, selective, and precise tool for quantifying sulfamic acid in fertilizers, overcoming limitations of ion chromatography in high-organic matrices. Its strong performance in calibration and spike recovery tests supports its adoption for regulatory and quality-control purposes.

References

1. Notification Regarding Determination of the Official Standard for Ordinary Fertilizer Based on the Fertilizers Regulation Act, Japan’s Ministry of Agriculture, Forestry and Fisheries Notification No. 284, Final Revision, December 5, 2013.
2. Food and Agricultural Materials Inspection Center (FAMIC): Testing Methods for Fertilizers (2013).
3. Hiroi T., Shirai Y.: Simultaneous Determination of Sulfamic Acid and Ammonium Thiocyanate in Ammonium Sulfate by Nonsuppressed Ion Chromatography, Research Report of Fertilizer, 5, 1–12 (2012).