Air Cell Mode of the Agilent 9500 ICP-QQQ with Dual-Cell System

Significance of the topic

Interference control is a critical challenge in inductively coupled plasma mass spectrometry (ICP-MS), particularly when measuring trace elements in complex matrices such as soils, seawater, and foods. Reliable suppression of polyatomic and multiply charged interferences directly improves limits of detection, quantification accuracy, and method robustness. The Agilent 9500 ICP-QQQ introduces an operational mode that uses ambient laboratory air as a reaction gas in its Dual-Cell System (DCS), offering a simple, low-maintenance approach to interference reduction without the need for external gas cylinders.

Objectives and overview of the study

This technical overview explains the principles and practical performance of the Air cell mode available on the Agilent 9500 triple quadrupole ICP-MS (ICP-QQQ). It compares Air cell mode with Advanced Helium Mode (AHM) and demonstrates how the combination of these modes—implemented in a standard multitune method—handles a broad range of spectral interferences. The note presents experimental examples showing improved background equivalent concentrations (BECs), better detection limits, and increased analytical selectivity for a variety of elements and challenging matrices.

Methodology

The 9500 ICP-QQQ operates in MS/MS mode with Q1 and Q2 as mass filters and a collision/reaction cell (CRC) between them (the DCS). Two principal interference reduction strategies are available:

• Advanced Helium Mode (AHM): a collision-KED approach using helium to exploit differences in collisional cross-sections, effective for many polyatomic interferents but limited against doubly charged ions (M2+).
• Air cell mode: uses filtered ambient air (chiefly O2 and N2) as a reactive cell gas to promote selective ion–molecule reactions, converting analyte or interfering ions to oxide or higher-oxide product ions and enabling MS/MS mass-shift or on-mass strategies.

Key operational features of Air cell mode:

• Ambient air supplies O2 for reactive chemistry and N2 for thermal damping; laboratory atmospheric pressure suffices so no compressor or cylinder is required.
• An integrated air-cell gas filter removes moisture and hydrocarbons to prevent uncontrolled side reactions; an automatic control valve minimizes air exposure and extends filter life.
• Air cell chemistry is compatible with MS/MS mass-shift workflows: Q1 restricts precursor m/z entering the cell and Q2 selects product m/z, enabling separation of analyte product ions from interferences.

Used Instrumentation

Equipment described and used in the presented examples:

• Agilent 9500 ICP-QQQ (triple quadrupole ICP-MS) with Dual-Cell System (DCS).
• Onboard Air cell gas filter and automatic control valve for ambient air supply.
• Agilent OpenLab ICP-MS software with a standard multitune method combining AHM and Air cell modes.

Main results and discussion

Experimental comparisons demonstrate that Air cell mode extends interference control beyond what AHM alone can achieve:

• Suppression of doubly charged REE interferences on As and Se: AHM reduces polyatomic interferences (e.g., ArCl+, CaCl+) but fails against REE2+. Air cell mode converts As and Se to oxide product ions (AsO+, SeO+), shifting analyte signals away from REE2+ isobars and reducing both interference types.
• Improved analysis of S, P, and Si: elements prone to O2+, NO+, and N2+ interferences show lower BECs and detection limits in Air cell mode relative to AHM, with enhanced sensitivity from the mass-shift approach.
• Germanium and gadolinium in light-REE matrices: Ge suffers from Nd2+/Sm2+ overlaps and Gd from LaO+/PrO+. AHM cannot mitigate M2+ on Ge; Air cell mass-shift to GeO+ achieves low-level detection and substantially lower BECs. For Gd, Air cell mode detects GdO+, further improving BECs beyond AHM.
• Gold in tantalum-containing samples: Au+ is largely unreactive with O2 so mass-shift is ineffective. However, the interfering TaO+ reacts further in air to form TaOO+, allowing on-mass detection of Au at m/z 197 with reduced interference—Air cell mode outperforms AHM in this case.
• Mo/W oxide interferences on Cd and Hg: MoO+ and WO+ convert to higher oxides (MoOO+, WOO+) in air while Cd and Hg remain largely unreactive, enabling selective quantification of Cd and Hg in samples containing Mo or W.

Overall, combining AHM and Air cell mode in a multitune method provides complementary suppression of polyatomic and multiply charged interferences, yielding lower BECs and better limits of detection across diverse sample types.

Benefits and practical applications

Practical advantages of Air cell mode include:

• No need for external reactive gas cylinders (O2, N2O) for many routine analyses—laboratory air is sufficient, simplifying setup and reducing running costs and cylinder management.
• Effective suppression of both polyatomic and doubly charged interferences, improving accuracy for elements that are otherwise difficult by single-quadrupole ICP-MS.
• Integrated filtering and valve control reduce contamination and extend service intervals, enhancing stability and reproducibility.
• Flexibility to use external high-purity O2 or N2O when maximum sensitivity or lowest BECs are required for specific elements.

Target applications include environmental monitoring, food safety, soil and sediment analysis, seawater analysis, and industrial quality control where complex matrices contain REEs, high-Mo/W levels, or matrix-derived polyatomic species.

Future trends and potential uses

Expected directions and opportunities:

• Expanded MS/MS tuning strategies that exploit ambient-air chemistry to tailor product-ion formation for additional difficult analytes.
• Further optimization of inline air filtration and automated gas-path controls to reduce maintenance and improve long-term reproducibility.
• Wider adoption of multitune, cylinder-free workflows in regulated laboratories to streamline method deployment across networks of instruments.
• Integration of data-driven methods (software presets, AI-assisted tuning) to automatically select AHM vs Air cell or combined modes based on matrix and analyte lists.

Conclusion

Air cell mode on the Agilent 9500 ICP-QQQ provides a simple, robust, and effective interference-reduction strategy by using filtered laboratory air as a reactive cell gas. When combined with AHM in MS/MS workflows, it addresses a broad class of interferences—polyatomic and doubly charged—improving BECs, detection limits, and analytical confidence without the operational overhead of external gas cylinders. The approach is particularly valuable for laboratories that require routine, interference-free multi-element analysis across challenging matrices.

References

1. Agilent Technologies. Dual-Cell System (DCS) and Advanced Helium Mode (AHM), publication 5994-8985EN.
2. Kubota T. Fast and Reliable Analysis of Soil and Sediments using ICP-MS with an Innovative Cell. Agilent publication 5994-9128EN.
3. Zou A.; Yamanaka M.; Sugiyama N. Direct Analysis of Seawater using ICP-QQQ and Integrated Advanced Valve System. Agilent publication 5994-8988EN.
4. Santhosh S. Automated Analysis of Foods by ICP-QQQ with Discrete Sampling and Autodilution. Agilent publication 5994-9095EN.
5. Sugiyama N.; Nakano K. Reaction data for 70 elements using O2, NH3, and H2 gases with the Agilent 8800 Triple Quadrupole ICP-MS. Agilent publication 5991-4585EN.