ORS4 AND HELIUM MODE FOR MORE EFFECTIVE INTERFERENCE REMOVAL IN COMPLEX SAMPLES

Importance of the topic

Modern elemental analysis in complex samples demands reliable interference removal to achieve accurate, low-level determinations. Collision/reaction cells (CRCs) in inductively coupled plasma mass spectrometry (ICP-MS) address polyatomic overlaps that arise from sample matrices. Using inert gases such as helium in collision mode simplifies method development, prevents new interferences, and preserves sensitivity, making it highly relevant for environmental, clinical, and industrial laboratories.

Objectives and study overview

This application note from Agilent Technologies evaluates the performance of the 4th generation Octopole Reaction System (ORS4) in the 7800 Quadrupole ICP-MS using helium collision mode. The aim is to compare helium mode with no-gas and hydrogen reaction mode for removing multiple polyatomic interferences in a challenging mixed acid matrix. Method simplicity, interference removal efficiency, and retention of analyte sensitivity are key focus points.

Methodology and instrumentation

The study employs the Agilent 7800 ICP-MS equipped with the ORS4 cell and ShieldTorch ion source. Three cell conditions are tested:

• No gas (standard vacuum mode)
• Hydrogen reaction mode (reactive gas)
• Helium collision mode (inert gas with kinetic energy discrimination)

The test matrix is a blank containing 5% HNO3, 5% HCl, 1% H2SO4 and 1% isopropanol. A 10 ppb multi-element spike is used to assess sensitivity under helium mode. Spectra of first-row transition elements are recorded on a uniform intensity scale for direct comparison.

Main results and discussion

No-gas measurements reveal extensive molecular interferences from the mixed matrix, obscuring analyte signals. In hydrogen reaction mode, some targeted interferences are reduced but unreactive overlaps remain and new reaction products emerge, complicating analysis. In contrast, helium collision mode leverages kinetic energy discrimination (KED) to collide larger polyatomic ions more frequently, dissipate their energy, and exclude them from the mass analyzer. This approach effectively removes all observed interferences without generating new ones and maintains high analyte signal, as demonstrated by the clear detection of a 10 ppb spike.

Practical benefits and applications

Helium collision mode on the ORS4 cell offers:

• Broad-spectrum removal of polyatomic interferences across multiple masses
• Stable performance regardless of unknown or variable sample matrices
• No formation of secondary interferences
• Preservation of analyte sensitivity and low detection limits
• Simplified method development without prior matrix identification

This makes it ideal for multi-element analysis in environmental monitoring, food safety, geochemistry, clinical research and QA/QC in manufacturing.

Future trends and potential applications

As complex sample matrices become more common, helium collision mode will likely be integrated into routine workflows. Advances may include:

• Automated optimization of KED voltages for different sample types
• Combination with high-resolution mass analyzers for even greater interference avoidance
• Miniaturized or benchtop ICP-MS systems leveraging helium collision for field-based testing
• Software-driven diagnostics to predict and flag potential interferences in real time

Such developments will further streamline elemental analysis and expand its accessibility.

Conclusion

Helium collision mode in the Agilent 7800 ICP-MS with ORS4 offers a robust, broadly applicable solution for interference removal in complex matrices. By eliminating polyatomic overlaps without forming new interferences or sacrificing sensitivity, it simplifies multi-element quantitation and supports high-throughput, accurate analysis across diverse application areas.

Reference

Agilent Technologies, 7800 Quadrupole ICP-MS with ORS4 and Helium Mode Application Note, Publication 5990-7574EN, June 2015