ENHANCED HELIUM MODE CELL PERFORMANCE FOR IMPROVED INTERFERENCE REMOVAL IN ICP-MS

Significance of the Topic

The accurate quantification of trace elements by ICP-MS is often compromised by polyatomic interferences. Helium collision mode with kinetic energy discrimination (KED) offers a robust, universal approach to suppress multiple interferences simultaneously, even in complex or variable sample matrices. This technique is particularly valuable in environmental, clinical and industrial analyses where unknown or fluctuating matrices challenge conventional interference removal methods.

Objectives and Study Overview

This study evaluates the enhanced performance of helium collision mode in the fourth-generation Octopole Reaction System (ORS4) on the Agilent 7800 ICP-MS. The goal is to demonstrate how instrument modifications improve collision-induced dissociation (CID) and kinetic energy discrimination, leading to lower backgrounds and detection limits for key analytes such as selenium, sulfur, phosphorus and iron.

Methodology and Instrumentation

Analyses were performed on an Agilent 7800 Quadrupole ICP-MS equipped with the ORS4 collision/reaction cell. Key enhancements include:

• Longer, higher-frequency octopole for increased collision rates.
• Higher helium cell gas flow to boost cell pressure.
• New ion lens design providing greater cell bias voltage for elevated collision energies.
• Advanced gas control unit for rapid gas switching.

Helium mode at 100 eV ion energy was compared to conventional 20 eV operation to assess improvements in CID and interference suppression.

Main Results and Discussion

The ORS4 delivers a center-of-mass collision energy of approximately 4.9 eV, exceeding the 1.33 eV bond energy of Ar2. This results in effective dissociation of Ar2 interferences and enhanced separation between residual kinetic energies of analyte and interfering ions. Experimental data show:

• Significant reduction of the background equivalent concentration (BEC) for 78Se to ~2 ppt.
• Improvement of Se detection limits from ~150 ppt (ORS2) to <5 ppt (ORS4).
• Enhanced detection limits and interference removal for S, P and Fe, often eliminating the need for reactive cell gases.

These findings illustrate that higher collision energy and optimized cell conditions in the ORS4 yield superior interference removal and sensitivity.

Benefits and Practical Applications

The enhanced helium mode in ORS4 enables:

• Simplified method development by relying solely on inert collision gas.
• Lower detection limits in ppt range for challenging analytes.
• Increased robustness when analyzing complex or unknown matrices.
• Reduced reliance on reactive gases, cutting operational costs and complexity.

This makes the technique highly attractive for environmental monitoring, food safety testing, clinical assays and quality control in industrial workflows.

Future Trends and Applications

Ongoing developments are likely to focus on further increasing collision cell energy, refining ion optics and expanding collision gas chemistries. Integration with high-throughput automation and coupling with separation techniques (HPLC, GC) will broaden application scope. Advances in data processing and machine learning could enable real-time optimization of cell conditions for dynamic matrix adaptation.

Conclusion

The ORS4 helium collision mode on the Agilent 7800 ICP-MS demonstrates marked improvements in interference removal and detection limits. Higher collision energies enable both effective dissociation of polyatomics and enhanced kinetic separation, delivering reliable ppt-level quantification without reactive gases. This advancement streamlines trace element analysis across diverse fields, ensuring robust performance in complex sample matrices.