Ultra-Trace ICP-MS Analysis of Metals in Mineral Reference Materials

Significance of the topic

The accurate measurement of trace and major elements in geological samples is critical for mineral exploration, quality control in mining operations and environmental monitoring. Traditional workflows often require separate analyses for high-concentration elements (using ICP-OES) and trace elements (using ICP-MS), increasing cost and turnaround time. A unified approach that can handle both concentration extremes in a single run can significantly enhance laboratory productivity and reduce per-sample expenses.

Objectives and overview of the study

This study evaluated the performance of the Agilent 7900 ICP-MS equipped with Integrated Sample Introduction System for Discrete Sampling (ISIS-DS), Ultra High Matrix Introduction (UHMI) and the fourth-generation Octopole Reaction System (ORS4) in helium collision mode. The aim was to demonstrate that a single ICP-MS method can quantify 45 analyte elements plus three internal standards across a wide concentration range in acid-digested geological reference materials, maintaining low detection limits, high accuracy and long-term stability.

Methodology and instrumentation

Sample preparation:

• Six certified mineral reference materials (OREAS and ALS CRMs) were digested in 20 mL of 75% aquaregia at 160–210 °C for 60–90 min.
• After cooling, samples were diluted to 50 g in auto-sampler tubes and spiked online with 1% butanol plus Rh and Ir internal standard solution.
• Each batch included four replicates per CRM and two preparation blanks.

Collision cell mode and rinse:

• He collision mode was applied to control polyatomic interferences and extend the upper dynamic range of low-mass elements.
• A 3% HCl/2% HNO₃ rinse containing 20 mM thiourea minimized carryover of “sticky” elements like Au, Sb and W.

Instrumentation used

• Agilent 7900 ICP-MS with nickel cones, MicroMist nebulizer and UHMI system in robust mode.
• Integrated Sample Introduction System (ISIS-DS) for discrete sample uptake and rapid rinse.
• ORS4 collision cell operating in helium mode to suppress interferences.

Main results and discussion

Calibration and detection limits:

• Calibration was linear over element-specific ranges up to 5000 ppb (e.g., Ca, Fe in He mode) with method detection limits in the low µg/L range, corresponding to ppb levels in rock samples.
• Continuing calibration verification recoveries remained within ±20% over a six-hour sequence of 240 analyses.

Accuracy and precision:

• Recoveries for major and trace elements in OGGeo08 and MRGeo08 CRMs were generally between 75% and 110% of certified values.
• Replicate precision (%RSD, n=37) was typically better than 5% across the mass range.

Benefits and practical applications of the method

This unified ICP-MS approach allows simultaneous quantification of major and trace elements in a single 90 s run per sample. Key advantages include:

• Reduced analysis time and cost by eliminating parallel ICP-OES runs.
• Improved interference control and lower detection limits through He collision mode.
• High matrix tolerance up to 25% TDS with UHMI and minimal drift with ISIS-DS.

Future trends and potential uses

Further developments may include automation of sample digestion, integration with high-throughput robotics and expanded collision/reaction cell gas chemistries for even more challenging matrices. The methodology could be adapted to environmental, industrial and metallurgical applications requiring rapid multi-element analysis.

Conclusion

The Agilent 7900 ICP-MS with UHMI, ISIS-DS and He mode demonstrated reliable, accurate, and fast analysis of 48 elements in acid-digested geological samples. It offers a practical solution for laboratories seeking to streamline workflows and lower analytical costs while maintaining high data quality.

References

1. Performance of the Agilent 7900 ICP-MS with UHMI for high salt matrix analysis, Agilent Technologies, publication 2014, 5991-4257EN.