Ultra-Trace Analysis of Metals in Mineral Reference Materials

Importance of the topic

The reliable quantification of trace and major metals in base metal ores is critical for the mining industry to assess resource value, optimize extraction, and ensure process control. Traditional methods like FAAS and ICP-OES involve flammable gases or high operational costs. A safer, lower-cost, and field-deployable alternative can deliver rapid feedback on ore composition, improving decision making at remote exploration sites.

Study objectives and overview

This study aimed to demonstrate the capability of Agilent 4200 Microwave Plasma Atomic Emission Spectroscopy (MP-AES) to:

• Accurately determine 12 elements (Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Ti, W, Zn) in mineral reference materials.
• Validate precision and accuracy across certified reference materials and a real chromite ore core.
• Evaluate operational benefits under remote, unattended conditions without flammable gases.

Instrumentation used

The core analytical platform featured:

• Agilent 4200 MP-AES with microwave-induced, nitrogen-based plasma.
• Glass concentric nebulizer, double-pass glass cyclonic spray chamber, easy-fit torch.
• Nitrogen supply via Dewar or 4107 nitrogen generator for field deployment.
• MP Expert software with continuous wavelength coverage to minimize spectral interferences.

Methodology

Ore samples (~0.2 g) and 12 certified reference materials were digested using infrared-assisted acid mixtures (aqua regia, reverse aqua regia, phosphoric or phosphoric/sulfuric acid) to 25 mL. Calibration standards (1, 5, 10 mg/L) were prepared in 1% HNO3. Key MP-AES parameters included a pump rate of 10 rpm, nebulizer flow of 0.7–1.0 L/min, 3 s read time, and auto background correction. Wavelengths were selected to avoid interelement overlap across the broad concentration range.

Main results and discussion

All elements exhibited linear calibration (R²>0.999). Recoveries for 12 metals in CRMs ranged from 94% to 105% with RSDs below 2.5%. Analysis of ten sub-samples from a chromite ore core yielded Cr and Fe recoveries of 98%–104% with RSD ≤1.5%, demonstrating excellent precision and repeatability in real samples.

Benefits and practical applications

The MP-AES method offers:

• Elimination of flammable and high-cost gases, enhancing safety and reducing operational expenses.
• Wide linear dynamic range and lower detection limits than FAAS, enabling simultaneous quantification of trace to major levels.
• Automated, unattended operation suitable for remote field laboratories.

Future trends and opportunities

Further developments may include integration of automated sample preparation, expansion to additional elements and isotopes, and coupling with online data analytics for real-time ore body characterization. Portable MP-AES systems could support on-site decision making, environmental monitoring, and exploration surveys.

Conclusion

The Agilent 4200 MP-AES provides a robust, accurate, and cost-effective approach for multi-element analysis of base metal ores. Its nitrogen-based plasma eliminates safety concerns associated with flammable gases, while delivering high precision across a broad concentration range, making it ideal for both laboratory and field applications.

References

• [1] Y. Wang, L.A. Baker, E. Helmeczi, I.D. Brindle, Rapid high-performance sample digestion of base metal ores using high-intensity infrared radiation with determination by nitrogen-based microwave plasma optical spectrometry, Analytical Chemistry Research, 2016, doi:10.1016/j.ancr.2016.02.002