Unmatched Removal of Spectral Interferences in ICP-MS Using the Agilent Octopole Reaction System with Helium Collision Mode

Importance of the Topic

Inductively coupled plasma mass spectrometry (ICP-MS) is a cornerstone technique for multi-element trace analysis across environmental, biological and industrial matrices. However, its performance is often compromised by spectral interferences arising from plasma- and matrix-derived polyatomic ions. The introduction of a helium collision mode within the Agilent Octopole Reaction System (ORS) addresses this challenge by employing kinetic energy discrimination (KED) to separate analyte ions from larger polyatomics, enabling robust interference removal without complex method development.

Study Objectives and Overview

This study evaluates the capability of the Agilent 7500ce ICP-MS, equipped with the ORS and operated in a single set of He collision gas conditions, to remove a broad spectrum of polyatomic interferences in a highly complex synthetic sample matrix. Key aims include demonstrating universal interference attenuation, preserving analyte sensitivity and confirming accurate multi-element quantification at trace levels.

Methodology and Instrumentation

A synthetic matrix containing 1 % HNO₃, 1 % HCl, 1 % H₂SO₄, 1 % butan-1-ol and 100 mg/L each of Na and Ca was prepared to generate extensive plasma- and matrix-based interferences across m/z 50–80. An Agilent 7500ce ICP-MS was used under standard high-matrix tuning (CeO/Ce ≈ 0.8 %), with no parameter adjustment for specific interferences. The ORS cell was pressurized with 5.5 mL/min He gas, leveraging the ShieldTorch interface for tight ion energy control and the octopole cell for enhanced collision frequency and focusing efficiency.

Main Results and Discussion

Comparative spectra acquired in no-gas mode and He collision mode on identical intensity scales revealed:

• Complete removal of high-intensity interferences such as 40Ar₁₆O⁺, 40Ar₂⁺, 40Ar¹²C⁺ and matrix-derived polyatomics (S₂⁺, ClO⁺) under He mode.
• Reduction of low-intensity, variable interferences to negligible levels, ensuring stable backgrounds independent of matrix composition.
• Successful recovery of a 5 ppb multi-element spike (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, As, Se) in the challenging matrix, with clear isotopic pattern matches and minimal residual ArOH and Ar₂ signals.

These results confirm that a single He collision mode setting universally attenuates both plasma- and matrix-derived interferences, enabling accurate isotopic measurements at trace levels without mathematical corrections.

Benefits and Practical Applications

The He collision mode on the 7500ce ORS offers several advantages:

• Universal interference removal for all polyatomic species under fixed conditions, simplifying multi-element workflows.
• No reactive gas consumption or analyte reaction, preserving sensitivity and internal standard integrity.
• Elimination of method development for individual interferences, reducing setup time and operator expertise requirements.
• Freedom to select optimal sample digestion media (nitric, hydrochloric or sulfuric acid) without generating new interferences.
• Applicability to transient signals from chromatography or laser ablation, supporting hyphenated techniques and semiquantitative screening.

Future Trends and Potential Applications

Expansion of He collision mode use is anticipated in high-throughput QA/QC laboratories, environmental monitoring and biomedical trace metal analysis. Potential developments include:

• Integration with advanced sample introduction systems (e.g., laser ablation, HPLC-ICP-MS) for speciation studies.
• Exploration of alternative inert collision gases or mixed gas modes to further enhance selectivity.
• Automated diagnostics and self-optimizing software to monitor cell conditions and maintain performance across diverse matrices.

Conclusion

The Agilent ORS in He collision mode enables truly universal polyatomic interference removal for ICP-MS, combining simple operation with high analytical performance. By decoupling interference management from analyte reactivity and matrix composition, it delivers accurate, multi-element quantification in complex samples without method development, expanding the versatility and reliability of routine and research applications.

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