Determination of Macro and Micronutrients in Fertilizers using MP-AES

Significance of the topic

Fertilizers are essential to agriculture, supplying macro- and micronutrients that regulate plant growth and crop yields. Precise quantification of these elements ensures product quality, compliance with international and regional regulations (e.g., EU Regulation EC 2003/2003, US EPA, China MOA), and environmental safety.

Objectives and study overview

This study evaluates the performance of Microwave Plasma-Atomic Emission Spectroscopy (MP-AES) for the rapid determination of six key nutrients (K, Ca, Mg, B, Mn, Mo) in mineral and organo-mineral fertilizers. It aims to demonstrate accuracy, linearity, and throughput compared to traditional techniques.

Methodology and instrumentation

Sample preparation:

• Inorganic fertilizers (samples A, B): Dilution 1:2000 in 1% HNO₃.
• Organo-mineral fertilizer (sample C): Microwave-assisted acid digestion using HNO₃/H₂O₂ in a PTFE vessel at 200 °C.

Instrumentation:

• Agilent 4200 MP-AES system with OneNeb inert nebulizer and double-pass cyclonic spray chamber.
• Nitrogen plasma generated from cylinder supply.
• MP Expert software for automatic background correction, nebulizer flow optimization, and method control.

Key operating parameters:

• Pump speed: 15 rpm; sample uptake delay: 15 s; stabilization time: 15 s; three replicates per measurement.
• Element-specific wavelengths and nebulizer flow rates were optimized (e.g., Mn 403.076 nm at 1.0 L/min; Ca 643.907 nm at 1.0 L/min).

Key results and discussion

Calibration and linearity:

• Three-point calibration over sub-ppm to tens of ppm ranges.
• Correlation coefficients ≥ 0.998 for all elements, indicating excellent linearity.

Accuracy and recovery:

• Spike-recovery tests in all matrices yielded recoveries within ± 10% of nominal values.

Performance advantages:

• Simultaneous analysis of macro- and micronutrients in a single run without matrix modifiers.
• Wide dynamic range minimizes the need for sample reanalysis.

Benefits and practical applications

MP-AES offers several advantages over conventional FAAS and ICP-AES:

• Elimination of flammable or toxic gases (e.g., acetylene), enhancing lab safety and enabling unsupervised operation.
• Lower operational costs using nitrogen plasma and reduced maintenance (no lamp changes for multiple elements).
• Improved throughput by analyzing multiple elements in one run.

This method is suitable for routine quality control in fertilizer production, regulatory compliance testing, and environmental monitoring.

Future trends and potential applications

Emerging directions include:

• Integration of MP-AES with automated sample preparation and robotic platforms.
• Development of portable or field-deployable plasma spectrometers for on-site soil and fertilizer analysis.
• Application of advanced chemometric and AI-driven models for real-time data interpretation and process control.

Conclusion

The Agilent 4200 MP-AES method delivers reliable, accurate, and efficient quantification of major and trace nutrients in fertilizers. It outperforms traditional FAAS in sensitivity, linearity, safety, and cost, making it an ideal tool for modern agricultural analytics.

References

• Regulation (EC) No 2003/2003 of the European Parliament and of the Council on fertilizers, Official Journal L 304, 2003.
• Fertilizer Regulations, Decreto Legislativo n.75/2010, Italy.
• US Environmental Protection Agency. Laws and regulations for agricultural operations.
• People's Republic of China, Implementation Regulations of the Food Safety Law, Ministry of Agriculture, 2017.