Determination of Multiple Elements in Fertilizers using the Agilent 4210 MP-AES

Importance of the Topic

Accurate determination of macro- and micronutrients alongside potentially toxic heavy metals in commercial fertilizers is critical to ensure agronomic effectiveness and environmental safety. Brazilian regulations mandate strict upper limits for contaminants such as Cd, Cr, Ni, and Pb to protect crop quality and prevent groundwater pollution.

Objectives and Study Overview

This study aimed to develop and validate a single-run analytical method for 17 elements in fertilizers using the Agilent 4210 Microwave Plasma-Atomic Emission Spectrometer (MP-AES). The approach was designed to meet Brazilian Ministry of Agriculture Ordinance n.27 (Normative Instruction n.7), assessing accuracy, sensitivity, precision, and long-term stability.

Methodology and Instrumentation

A closed-vessel microwave digestion protocol was applied to five commercially sourced fertilizer types (urea, foliage, organic, NPK, mineral) and a certified reference material (NIST 695). Key instrument and sample preparation details included:

• Instrumentation: Agilent 4210 MP-AES with nitrogen plasma (Agilent 4107 generator), double-pass cyclonic spray chamber, OneNeb Series 2 nebulizer.
• Operating Conditions: three replicates; read time 3 s (Cd 10 s, Pb 5 s); uptake 15 s; stabilization 15 s; nebulizer flow 0.5 L/min; pump speed 12 rpm.
• Digestion Program: three steps—ramp to 100 °C (10 min), to 150 °C (10 min), to 170 °C (10 min hold for 5 min).
• Calibration Standards: mixed single-element stocks in 10 % HCl; concentration ranges 0.2–50 mg/L depending on element.

Key Results and Discussion

• Linearity: correlation coefficients R>0.999 for all 17 elements across six-point calibrations.
• Limits of Quantitation: LOQs (calculated from 10× blank SD × 200× dilution) were below or meeting regulatory thresholds for all analytes.
• Accuracy: SRM recoveries ranged from 89 % to 116 % with RSD <10 % (n=3), demonstrating method validity.
• Precision and Stability: continuous measurement of SRM over 7 hours (~100 injections) yielded RSD <2.4 %, indicating robust long-term performance.
• Fertilizer Analysis: all heavy metal concentrations (Cd, Cr, Ni, Pb) were below the maximum permitted levels. Nutrient contents (K₂O, P₂O₅, B, Zn) generally matched or exceeded declared values; minor deviations likely reflect sample inhomogeneity.

Benefits and Practical Applications

The Agilent 4210 MP-AES method offers significant advantages over traditional FAAS and ICP-OES:

• No hazardous gases or hollow cathode lamps required; nitrogen generator runs on air.
• Simultaneous multi-element capability reduces analysis time and contamination risk from multiple dilutions.
• Lower cost-of-ownership, high throughput, and compatible with autosamplers and valve systems for automated workflows.

Future Trends and Potential Applications

• Integration with automated sample preparation and autosampler platforms to further increase throughput.
• Miniaturized and portable MP-AES systems for in-field fertilizer quality screening.
• Coupling with chemometric data analysis and digital reporting for real-time regulatory compliance.
• Extension to speciation studies and assessment of emerging contaminants in agriculture.

Conclusion

The developed MP-AES method enables reliable, sensitive, and efficient quantification of essential nutrients and trace contaminants in commercial fertilizers. It meets regulatory requirements, minimizes operational hazards, and supports quality control in fertilizer production and agronomical research.

References

1. Pelizzaro V., et al. Determination of Macro and Micronutrients in Fertilizers using MP-AES. Agilent Tech. 5994-0566EN.
2. Li W., et al. Talanta 112, 43–48 (2013).
3. Lima A.F., et al. Microchem J. 118, 40–44 (2014).
4. Lima A.F., et al. Applied Acoustics (in press).
5. Machado R.C., et al. J. Agric. Food Chem. 65, 4839–4842 (2017).
6. Brazilian Ministry of Agriculture Ordinance n.27 (2016).
7. NIST SRM 695 Certificate of Analysis.