Rapid determination of gold in geological samples using the Agilent 4210 MP-AES

Importance of the Topic

Accurate and rapid gold determination in geological samples is essential for mining operations, exploration, and quality control laboratories.
The choice of analytical technique affects safety, operating costs and throughput.
Traditional flame AAS relies on flammable gases, whereas MP-AES uses nitrogen, offering a safer and more economical alternative.

Objectives and Study Overview

This study evaluates the Agilent 4210 MP-AES equipped with the AVS 4 valve system for gold analysis in samples prepared by fire assay.
Key aims were to assess detection limits, linear dynamic range, sample throughput, long-term stability and comparison with flame AAS performance.

Methods and Instrumentation

The instrument configuration included:

• Agilent 4210 MP-AES with built-in AVS 4 four-port switching valve controlled by MP Expert software
• SPS 4 autosampler with humidifier accessory
• Meinhard nebulizer, single-pass glass cyclonic spray chamber and easy-fit torch
• Dual peristaltic pump tubing (“rapid flow” concept) to double uptake flow and reduce sample uptake time by 40%

Analytical parameters:

• Wavelength: Au 267.595 nm
• Read time: 1 s, replicates: 3
• Pump speed: 15 rpm (normal), 80 rpm (uptake/rinse)
• Nebulizer flow: 0.85 L/min
• AVS delays: uptake 9 s, switch 7 s, rinse 5 s, stabilization 5 s

Sample preparation:

• Six geological digests and three reference materials (SL76, OxP116, BP-13) prepared by fire assay
• Final matrix: 30% aqua regia in ultrapure water
• Calibration standards: 2.5–100 mg/L Au in 30% aqua regia

Main Results and Discussion

Calibration and sensitivity:

• Linear calibration from 1 ppm to 100 ppm with R² > 0.999
• Method detection limit (MDL): 7.2 µg/L (Au 267.595 nm)

Accuracy and precision:

• Certified reference material recoveries within ±10%
• Comparison with flame AAS showed <10% difference for all samples
• Sample-to-sample time under 30 seconds
• Long-term stability over 3 hours: RSD <2%

The AVS 4 valve effectively diverts high-matrix solution during uptake and rinse, reducing wear on consumables and extending maintenance intervals.

Benefits and Practical Applications

• Eliminates use of flammable and costly gases
• Higher plasma temperature (5 000 K) yields improved matrix tolerance and lower detection limits compared to FAAS
• Wide dynamic range minimizes sample re-dilution
• Faster throughput suitable for high-volume geochemical labs
• Reduced consumable replacement lowers operating costs

Future Trends and Opportunities

Potential developments include:

• Extension to multi-element analysis of other precious and base metals
• Integration with automated sample preparation and robotics
• Coupling with separation techniques (e.g., flow injection) for speciation studies
• Implementation of data analytics and machine learning for method optimization

Conclusion

The Agilent 4210 MP-AES with AVS 4 switching valve provides a robust, safe and cost-effective alternative to flame AAS for gold determination in geological samples.
It delivers rapid analysis, low detection limits, excellent stability and reduced operational expenses.

References

• US Environmental Protection Agency, 40 CFR Appendix B to Part 136: Definition and Procedure for the Determination of the Method Detection Limit (Revision 1.11, July 2011)