WPC: High throughput and robust analysis of fertilizers using ICP-OES

Importance of the Topic

The accurate and rapid determination of both major and trace elements in fertilizers underpins regulatory compliance, product quality control, and environmental safety. Laboratories processing large numbers of fertilizer samples demand methods that combine high throughput, robustness to complex matrices, and minimal downtime.

Objectives and Study Overview

This work presents a case study for analyzing solid and liquid fertilizers using an advanced ICP-OES configuration. The goal was to develop a fast, robust method capable of quantifying regulated elements at low levels, with sample runtimes under one minute and minimal calibration drift over extended sequences.

Used Instrumentation

• ICP-OES: Thermo Scientific iCAP PRO XP Duo
• Autosampler: Thermo Scientific iSC-65 with “Step Ahead” feature
• Spray chamber: Glass cyclonic
• Nebulizer: Glass concentric
• Center tube: 2.0 mm quartz
• Torch: EMT glass
• Pump tubing: Tygon variants for sample, internal standard, and drain

Methodology

Samples were digested by microwave in HNO₃/HCl and diluted to 50 mL. A 100-fold dilution was applied to match EU Regulation 2019/1009 levels. Gold (200 µg/L) was added as a mercury stabilizer. The iCAP PRO XP operated in radial Intelligent Full Range (iFR) mode across 167–852 nm, with 5 s exposures and three replicates per element. The iSC-65’s Step Ahead feature overlapped rinse with data acquisition, achieving a total cycle time of 36 s per sample. Scandium at 10 mg/kg served as the internal standard for matrix correction.

Main Results and Discussion

Instrument detection limits ranged from 0.06 µg/kg (Co) to 8.64 µg/kg (K) at a 100× dilution. Calibration curves showed R² values >0.998 for all analytes. A 5-hour sequence including over 500 unknowns exhibited stable internal standard recoveries and no significant drift. Analysis of NIST SRM-695 and spiked samples yielded recoveries between 86.7 % and 101.4 %, demonstrating accuracy for both major nutrients (K, P, Ca, Mg) and trace contaminants (Cd, Pb, As).

Benefits and Practical Applications

• High throughput: 36 s per sample including uptake, analysis, and wash
• Robustness: minimal drift over >500 injections
• Regulatory compliance: LOQs meet EU 2019/1009 requirements
• Wide dynamic range: trace level to high-concentration elements in a single run

Future Trends and Potential Applications

Emerging demands for rapid soil and wastewater monitoring, battery material screening, and feed quality control can leverage this approach. Integration with ICP-MS could further enhance sensitivity for ultra-trace elements. Automation and multi-matrix calibration strategies are likely to extend the utility of high-speed ICP platforms.

Conclusion

A streamlined ICP-OES method using the iCAP PRO XP and iSC-65 autosampler delivers robust, high-throughput fertilizer analysis with quantification limits aligned to current regulations. Its broad applicability, speed, and reliability make it an attractive solution for diverse analytical laboratories.

References

1. Regulation (EU) 2019/1009 on the making available on the market of EU fertilizing products.