Analysis of noble metals at low levels in geological reference materials and ores

Importance of the Topic

Low-level detection of platinum group metals (PGMs) and gold in geological materials is critical to evaluate the economic potential of ore deposits, to ensure quality control in industrial catalysts and to support environmental monitoring. Accurate quantification at ultra-trace levels must overcome severe spectral interferences from matrix elements such as hafnium, tantalum, strontium and lead.

Aims and Study Overview

This application note demonstrates the capability of triple quadrupole ICP-MS (TQ-ICP-MS) to quantify ruthenium, rhodium, palladium, iridium, platinum and gold at ng·L⁻¹ levels in challenging matrices. Certified reference materials—a granodiorite (GSP 2, USGS) and a platinum ore (AMIS 0416)—were analyzed to verify interference removal, accuracy and precision.

Methodology and Instrumentation

Sample Preparation

• Acid digestion following a published protocol.
• Dilution in 3% HCl + 1% HNO₃.
• Spiking of GSP 2 with 10 and 25 ng·L⁻¹ for quality checks.

Instrument Configuration

• Thermo Scientific iCAP TQ ICP-MS with Teledyne CETAC ASX-560 autosampler.
• MicroMist quartz nebulizer (0.4 mL·min⁻¹), cooled cyclonic spray chamber at 2.7 °C.
• Quartz injector (2.5 mm), high-matrix Ni cones, RF power 1 550 W, nebulizer gas 1.11 L·min⁻¹.
• CRC reaction gases: He for SQ-KED, O₂ and NH₃ for TQ modes.
• QCell settings optimized for each gas: He 4.5 mL·min⁻¹, O₂ 0.7 mL·min⁻¹, NH₃ 0.37 mL·min⁻¹; cell biases adjusted accordingly.

Main Results and Discussion

Interference Removal

• TQ-O₂ and TQ-NH₃ modes achieved full suppression of HfO, HfOH, TaO and SrO interferences, compared with incomplete removal by He-KED.
• Blank equivalent concentration (BEC) improvements ranged from 7× to >200× for key isotopes.

Accuracy and Precision

• Spike recoveries in GSP 2 were 93–114% across PGMs and gold.
• Detection limits in TQ mode: Rh 0.04, Pd 0.23, Ir 0.09, Pt 0.08 and Au 0.12 ng·L⁻¹.
• Internal standard recoveries (115In, 209Bi) remained within ±30% over 11 h of analysis.

Reference Material Analysis

• AMIS 0416 results agreed with certified values for Rh, Pd, Ir and Pt (recoveries 89–108%).
• Gold recoveries were lower (52–66%), likely due to acid stabilization issues during sample preparation.

Benefits and Practical Applications

Triple quadrupole ICP-MS with reactive gases delivers robust interference removal, enabling reliable ultra-trace analysis of noble metals in complex geological and industrial matrices. This capability supports:

• Ore evaluation for mining decisions.
• Catalyst quality control in chemical and automotive industries.
• Environmental and forensic investigations.

Future Trends and Potential Applications

Advancements may include automated, high-throughput sample preparation workflows, expansion to other trace elements and isotopic systems, inline coupling with separation methods for speciation, portable or miniaturized TQ-ICP-MS systems and AI-driven tools for dynamic interference correction.

Conclusion

This study confirms that TQ-ICP-MS operated with oxygen or ammonia effectively eliminates isobaric and polyatomic interferences, achieving accurate, precise and low-level quantification of PGMs and gold in challenging sample matrices. A reliable sample preparation protocol remains essential to preserve analyte integrity.

Reference

Karandashev V.K., Khvostikov V.A., Nosenko S.V., Burmii Zh.P. Inorganic Materials 53 (2017) 1432–1441