Fast and Reliable Analysis of Soil and Sediments using ICP-MS with an Innovative Cell

Importance of the topic

The reliable, high-throughput measurement of trace and major elements in soils and sediments is essential for environmental monitoring, regulatory compliance, and contamination assessment. Inductively coupled plasma mass spectrometry (ICP-MS) is widely adopted for these tasks because of its high sensitivity and multi-element capability. Improvements that simplify interference control, increase matrix tolerance, and raise sample throughput directly benefit routine environmental laboratories by reducing per-sample cost, turnaround time, and method complexity.

Objectives and overview of the study

This application note evaluates the analytical performance and productivity of the Agilent 9500 triple-quadrupole ICP-MS (ICP-QQQ) equipped with a Dual-Cell System (DCS) and optional AVS MS discrete sampler for soil and sediment analysis. The method was developed to be compliant with EPA Method 6020B and to demonstrate: high sensitivity and low detection limits, robust interference control (including polyatomic and doubly charged M2+ interferences), long-term stability during extended sequences, and high sample throughput for routine environmental workflows.

Methodology

The study used a preset EPA 6020B method and UHMI-4 plasma conditions to standardize setup. Certified reference materials (CRMs) representing aqueous and predigested solid matrices were analyzed (NIST 1643f, River Sediment A/B, Soil A/B). Key methodological choices included:

• Use of Agilent 9500 ICP-QQQ with Dual-Cell System (DCS) and Ultra-High Matrix Introduction (UHMI).
• Operation primarily in Advanced Helium Mode (AHM) to replace multiple conventional gas modes, with Air cell mode (ambient O2) used selectively for oxygen-reactive analytes and M2+ removal.
• Acid matrix: 1% HNO3 + 0.5% HCl for blanks, standards, and diluted CRMs; internal standard mix (Sc, Ge, Rh, In, Tb, Lu) added online via the AVS MS seventh port.
• Six-point calibrations spanning trace and major element ranges; periodic QC with ICV and CCV blocks inserted every 10 samples.
• Short integration times and an AVS MS sample cycle optimized for rapid sample-to-sample analysis (~122 s per sample under the conditions used).

Used instrumentation

The principal instrumentation and relevant options reported in the study:

• Agilent 9500 ICP-QQQ with Dual-Cell System (DCS).
• Ultra High Matrix Introduction (UHMI) sample introduction to improve matrix tolerance.
• AVS MS discrete sampler (high-speed piston pump) integrated with SPS autosamplers for reduced sample exposure and improved throughput.
• Standard interface hardware: nickel sampler/skimmer cones, extraction/omega lens assembly and MicroMist nebulizer.

Main results and discussion

Analytical performance highlights from the study include:

• Limits of detection (LODs): Most trace analytes achieved low ng/L (ppt) LODs. AHM delivered excellent LODs for low-mass elements (e.g., Li, Be) traditionally measured in no-gas mode.
• Air cell mode markedly improved some LODs by using ambient O2 for mass-shift reactions: example, K LOD improved from ~0.97 µg/L (AHM) to ~0.029 µg/L (Air).
• Se LOD improved by about an order of magnitude in AHM compared with conventional He mode, even with shorter integration times.
• Interference control: AHM simplified workflow by replacing no gas, conventional He collision, and high-energy He modes with a single effective mode. Air mode used an O2 mass-shift to remove M2+ and polyatomic interferences (e.g., Sr2+ on 44Ca, REE2+ interferences on As and Se), restoring accurate quantification when M2+ species were present.
• Accuracy and precision: Recoveries for certified values in five CRMs and matrix spike samples were generally within ±10% of certified or spiked values. ICV and CCV recoveries met EPA Method 6020B limits (±10%).
• Long-term stability and robustness: The instrument analyzed 180 samples plus 38 QC solutions over ~8 hours with stable internal standard recoveries (>70% acceptance) and minimal drift, demonstrating high matrix tolerance and low matrix deposition during extended sequences.
• Matrix spike performance: MS/MSD RPDs were low (<3.5%) and spike recoveries were generally within ±10%, confirming method accuracy in high-matrix soils after dilution.

Benefits and practical applications

The approach combining the 9500 ICP-QQQ DCS with UHMI and AVS MS offers several practical benefits for environmental laboratories:

• Simplified gas-mode strategy: AHM reduces operational complexity by consolidating multiple collision/reaction modes into one, lowering method setup time and the risk of operator error.
• Improved sensitivity and lower LODs for problematic analytes (e.g., Se, low-mass elements) while maintaining interference control.
• Effective M2+ and polyatomic interference removal via Air cell mass-shift using ambient oxygen eliminates or reduces the need for O2 cylinders, reducing operating costs and logistics.
• High throughput: optimized sampling cycle and reduced integration times yield faster per-sample analysis suitable for routine high-volume labs.
• Robustness for high-matrix samples: UHMI and the DCS provide stable signals over long sequences, minimizing re-calibrations and downtime.

Future trends and possible uses

Key directions emerging from the work and likely future opportunities:

• Broader adoption of unified gas modes (like AHM) in routine environmental ICP-MS workflows to simplify method libraries and training.
• Expanded use of ambient-air-based reaction modes to reduce cylinder gases and lower operating costs, provided reaction chemistry remains well characterized for new analyte sets.
• Integration of high-speed discrete samplers and automated sample handling to further increase daily sample throughput and reduce carryover for demanding monitoring programs.
• Application of DCS-style cell strategies to increasingly complex matrices (e.g., sludges, digests with very high dissolved solids) and coupling with enhanced sample-introduction dilution strategies for extreme matrix loads.
• Continued validation against regulatory performance-based methods (e.g., EPA 6020 series) to support method harmonization in contract and regulatory laboratories.

Conclusion

The Agilent 9500 ICP-QQQ with Dual-Cell System and optional AVS MS sampler provides a robust, high-throughput solution for multi-element analysis of soil and sediment matrices in compliance with EPA Method 6020B. The combination of Advanced Helium Mode and Air cell mass-shift enables simplified interference management, low detection limits (often in the low ng/L range), and accurate recoveries across a broad concentration range. The platform demonstrated excellent long-run stability and accuracy for multiple CRMs and matrix spikes, supporting routine deployment in environmental testing laboratories seeking both performance and productivity gains.

References

1. U.S. EPA. 2014. Method 6020B (SW-846): Inductively Coupled Plasma–Mass Spectrometry, Revision 2.
2. Agilent Technologies. Dual-Cell System (DCS) and Advanced Helium Mode (AHM), publication 5994-8985EN.
3. Agilent Technologies. Air Cell Mode of the Agilent 9500 ICP-QQQ with Dual-Cell System, publication 5994-8987EN.
4. Sugiyama, N. Solving Doubly Charged Ion Interferences using an Agilent 8900 ICP-QQQ, Agilent publication 5994-1155EN.