Accurate measurement of elemental impurities in metals and metal alloys using triple quadrupole ICP-MS

Significance of the Topic

Understanding and controlling trace elemental impurities in high-performance metals and alloys is critical for industries such as aerospace and nuclear energy. Impurities like selenium in nickel alloys or cadmium in zirconium can degrade mechanical properties or compromise safety by altering neutron absorption. Accurate, interference-free quantification at sub-µg·L⁻¹ levels is therefore essential for material qualification and regulatory compliance.

Objectives and Study Overview

This work evaluates triple quadrupole ICP-MS (TQ-ICP-MS) strategies for measuring trace selenium in nickel matrices and arsenic/cadmium in zirconium alloys. The aim is to demonstrate how TQ mass shift and on-mass modes overcome spectral interferences that limit single quadrupole ICP-MS, and to compare detection limits and background equivalent concentrations under different reactive gas conditions.

Methodology

Metal and alloy samples were acid-dissolved and spiked with target analytes. Calibration standards (100–1 000 ng·L⁻¹) were matrix-matched to 100 mg·L⁻¹ nickel or zirconium (plus 1 mg·L⁻¹ tin for cadmium analysis). No internal standards were used due to matrix-matched calibration. Analyses compared single quadrupole ICP-MS with KED versus TQ-ICP-MS using oxygen or hydrogen in the collision/reaction cell.

Used Instrumentation

• Thermo Scientific iCAP TQ ICP-MS system
• Qtegra ISDS Software with Reaction Finder module
• Single element standard solutions and high-purity HCl digestion
• O₂ and H₂ reactive gases for mass shift and on-mass modes

Main Results and Discussion

Selenium in Nickel Alloys

• Single quadrupole ICP-MS with KED could not fully remove NiO⁺ and water-cluster interferences on 78Se⁺/80Se⁺.
• TQ mass shift mode (O₂ reaction to form SeO⁺) eliminated NiO⁺ and NiO·H₂O⁺ interferences by pre-filtering in Q1 and post-filtering in Q3.
• Using H₂ achieved higher sensitivity (9 700 cps·L·µg⁻¹ for 80Se⁺) but O₂ provided lower background equivalent concentrations (13.2 ng·L⁻¹) and limits of detection (5.1 ng·L⁻¹).

Arsenic and Cadmium in Zirconium Alloys

• Arsenic measurement at m/z 75 with helium KED removed ArCl⁺ interferences but suffered from ZrO⁺ formation when using O₂.
• TQ-O₂ mass shift mode converted As⁺ to AsO⁺, measured at m/z 91, yielding ~2× higher sensitivity and LOD ≈7 ng·L⁻¹ versus 17 ng·L⁻¹ by SQ-KED.
• Cadmium at m/z 111 was obscured by 94ZrO¹H⁺ and other ZrOₓ clusters in SQ mode.
• TQ on-mass mode with O₂ fully oxidized ZrO⁺ to ZrO₂⁺, removing the interference and resulting in BEC ≈10.6 ng·L⁻¹ and LOD 1.7 ng·L⁻¹ for 111Cd⁺.

Benefits and Practical Applications

TQ-ICP-MS dramatically improves accuracy and sensitivity for trace elements in complex metal matrices. It delivers robust interference removal without high-resolution mass analyzers and simplifies routine workflows. Industries benefit from reliable impurity profiling in turbine alloys, nuclear cladding materials and other critical components.

Future Trends and Opportunities

Advances may include automated reaction gas optimization via machine learning, expansion to additional challenging isotopes, integration with laser ablation for spatially resolved analysis and higher throughput protocols. Coupling TQ-ICP-MS with real-time data analytics will further enhance material qualification and process monitoring.

Conclusion

Triple quadrupole ICP-MS using both mass shift and on-mass modes effectively eliminates complex polyatomic interferences in metal and alloy matrices. The Qtegra Reaction Finder streamlines method development, making TQ-ICP-MS a powerful tool for routine trace element analysis in demanding industrial and research environments.

Reference

Marcus Manecki, Daniel Kutscher, Shona McSheehy Ducos; Thermo Fisher Scientific, Bremen, Germany; Application Note 43404; 2020.