Determination of 21 Elements in Fertilizers using Autodilution with ICP-OES

Significance of the Topic

The accurate determination of macro-, secondary, and micronutrients in fertilizers is essential to support sustainable agriculture, optimize crop yields, and ensure regulatory compliance. In addition, monitoring potential contaminants like heavy metals safeguards soil and environmental health. Analytical challenges arise from the need to measure up to 21 elements across wide concentration ranges and diverse sample matrices. High-throughput, automated methods can improve data quality, reduce errors, and accelerate decision making in quality control laboratories.

Aims and Study Overview

This study presents a streamlined approach for quantifying 21 elements in multinutrient fertilizers using an Agilent 5800 Vertical Dual View (VDV) ICP-OES coupled with an ADS 2 autodilutor. Objectives included:

• Automating calibration and sample dilution workflows to minimize human intervention
• Demonstrating method accuracy and precision across broad concentration ranges
• Assessing method detection limits and long-term analytical stability

Methodology and Instrumentation

Samples of a NIST fertilizer SRM and three commercial fertilizers (liquid, granular, and powdered) were microwave-digested in reverse aqua regia. The ICP-OES was equipped with a SeaSpray nebulizer, double-pass cyclonic spray chamber, semi-demountable VDV torch, and SPS 4 autosampler. The ADS 2 performed autocalibration (0–10 mg/L from a single stock), prescriptive dilutions, and reactive dilutions for over-range analytes. Automated Fitted Background Correction and an internal standard (Y at 371.029 nm) corrected matrix effects and interferences.

Main Results and Discussion

Calibration curves for all 21 elements exhibited correlation coefficients ≥ 0.99988. Method detection limits in-sample were below 1 mg/kg for most analytes. Analysis of the SRM showed recoveries within 90–105% for undiluted and 10× diluted measurements. Spike recovery tests on liquid fertilizer yielded 94–108% recoveries across 21 elements. Comprehensive sample analyses confirmed accurate quantification of both trace and major constituents. A nine-hour stability test with 482 measurements demonstrated recoveries within 100 ± 5% and RSDs < 3.5%, indicating robust instrument and dilution performance.

Benefits and Practical Applications

• Automated calibration reduces preparation time and consumable waste
• Reactive dilution eliminates prescreening and manual re-runs for high-concentration samples
• Summary Row feature streamlines data review by selecting optimal measurements
• High sample throughput with consistent accuracy and precision supports QA/QC workflows

Future Trends and Potential Applications

Advances in real-time data analytics and machine learning could further optimize autodilution parameters and anomaly detection. Integration of robotic sample handlers and direct soil or plant extract interfaces may extend this approach beyond fertilizers to complex environmental and agronomic matrices. Coupling ICP-OES with spectral libraries and predictive models could enable rapid field-to-lab feedback loops for precision agriculture.

Conclusion

The combination of Agilent 5800 VDV ICP-OES and ADS 2 autodilutor offers a robust, high-throughput solution for multi-element fertilizer analysis. Automated calibration, prescriptive and reactive dilutions, and advanced software features deliver accurate, precise results over a wide dynamic range while minimizing manual effort and error risk. This method supports regulatory compliance, product quality assurance, and efficient laboratory workflows.

References

1. AOAC Official Method 2017.02. Arsenic, Cadmium, Calcium, Chromium, Cobalt, Copper, Iron, Lead, Magnesium, Manganese, Molybdenum, Nickel, Selenium, and Zinc in Fertilizers. AOAC International, 2017
2. Agilent Technologies. Capabilities and Operation of the Advanced Dilution System 2, Publication 5994-7211EN
3. Agilent Technologies. Fitted Background Correction (FBC): Fast, accurate and fully automated background correction, Publication 5991-4836EN