Analysis of Soil and Sediments by ICP-MS with Advanced Sample Introduction Tools

Significance of the topic

The analysis of soils and sediments for inorganic contaminants is fundamental for environmental monitoring, regulatory compliance and risk assessment. Robust, high-sensitivity multi-element methods that tolerate complex matrices and reduce sample preparation time are essential for high-throughput environmental laboratories. This study demonstrates how advanced sample introduction accessories combined with a triple quadrupole ICP-MS platform can streamline workflows while maintaining the detection limits and accuracy required by EPA Method 6020B.

Objectives and study overview

The primary aim was to evaluate the analytical performance and practical benefits of combining the Agilent 9500 ICP-QQQ (with Dual-Cell System and UHMI) with two advanced sample-introduction tools: the Mira Mist nebulizer and an in-line particle filter (120 µm). Key goals included: demonstrating LODs and accuracy for trace and major elements, assessing washout and long-term stability without pre-filtration of digests, and verifying compliance with EPA 6020B criteria using certified reference materials (CRMs) and a real sediment sample.

Methodology

Samples and standards

• All standards, blanks and samples prepared in 2% HNO3 + 1% HCl (HCl added to stabilize Sb and Hg).
• Calibration: multi-point calibrations covering trace to major element ranges (examples: 0.05–1000 ppb for some elements; 100–100,000 ppb for major mineral elements).
• Internal standards: Sc, Ge, Rh, In, Tb, Lu added online via AVS MS seventh port.

Sample digestion and handling

• CRMs supplied as predigested solutions (NIST 1643f, River Sediment A/B, Soil A/B).
• Real estuarine sediment: microwave digestion (0.25 g sample; 9 mL HNO3 + 3 mL HCl), two-step temperature program (ramp to 180 °C, hold; then lower ramp to dissolve precipitates), final volume to 200 mL giving ~4.5% HNO3 and 1.5% HCl. No HF used (partial extraction, not full SiO2 decomposition).
• Spike experiments performed pre- or post-digestion at 50 µg/L in 50 mL digests for recovery checks.

Analytical strategy and QC

• All analytes measured predominantly in Advanced Helium Mode (AHM) using the Dual-Cell System; selected analytes (K, Ca, As, Se) also measured in Air cell mode to leverage O2 reaction chemistry where beneficial.
• Instrument autotune and EPA 6020B preset method used for method setup. ICV and CCV used for in-run QC; periodic CCV inserted after every 10 samples.

Instrumention used

• Agilent 9500 ICP-QQQ with Dual-Cell System (DCS) and Ultra High Matrix Introduction (UHMI).
• Optional AVS MS discrete-sampling valve system with high-speed piston pump and SPS autosampler integration.
• Mira Mist nebulizer (PEEK, larger internal diameter) to improve resistance to acids, solvents and particulates.
• In-line particle filter (Glass Expansion Guardian style) with ~120 µm element installed between autosampler probe and sample introduction line.
• Nickel interface cones and u-lens extraction/omega lens assembly.

Main results and discussion

Limits of detection and sensitivity

• Most trace analyte LODs were in the low ng/L (ppt) range, demonstrating the high sensitivity of the 9500 ICP-QQQ with AHM and Air cell modes.
• Mira Mist provided similar sensitivity and comparable LODs to the standard MicroMist despite slightly higher RSD due to its larger id; overall analytical performance remained excellent.

Washout and memory effects

• Washout tests for elements prone to memory effects (As, Se, Sb, Hg) showed equivalent washout efficiency with and without the in-line filter for most elements across multiple rinse cycles.
• Small transient difference for Sb on the first rinse was negligible in practical terms (residual memory far below levels that would affect soil analyses) and disappeared by the second rinse.

Long-term stability and robustness

• An extended sequence of 180 samples plus 38 QC samples (~8 hours continuous operation) demonstrated stable internal standard recoveries (>70% and no mass-dependent drift), consistent CCV performance, and minimal matrix deposition thanks to UHMI and matrix-tolerant plasma behavior.
• Sample-to-sample timing and AVS MS method parameters were unaffected by the presence of the small-volume in-line filter, enabling unchanged throughput whether the filter was installed or not.

Accuracy and recoveries

• Analysis of five CRMs (n=9 each) across major and trace elements yielded recoveries generally within ±10% of certified values, covering concentrations from sub-ppb to hundreds of ppm.
• Matrix spike recoveries (Soil A and real sediment spikes) were within ±10% for the majority of elements, confirming method accuracy for partial digests without HF.
• Where sample concentrations greatly exceeded spike levels, spike recovery interpretation was marked as compromised; otherwise recoveries supported method validity under EPA 6020B expectations.

Practical benefits and method advantages

• Reduced sample preparation: the Mira Mist nebulizer combined with the in-line filter allowed many sediment digests to be analyzed without a dedicated filtration step, saving time and consumables.
• Lower operational risk: improved resistance to clogging minimized downtime and maintenance related to blocked nebulizers or sample lines.
• Cost and workflow efficiency: Air cell mode uses ambient air as an O2 source via an integrated air filter, removing the need for O2 cylinders and simplifying gas handling while improving interference removal for oxygen-reactive species.
• High throughput: AVS MS integration and unchanged sample timing with the filter installed support robust laboratory productivity for environmental testing programs.

Future trends and potential applications

• Further adoption of matrix-tolerant nebulizers and in-line filtration will reduce pre-analysis steps for other challenging matrices (e.g., sludges, mine tailings), increasing laboratory efficiency.
• Advances in collision/reaction cell designs and gas strategies (e.g., dual-cell modes and ambient-air reaction gases) will continue to simplify interference control and reduce operating costs.
• Integration of automated sample handling and real-time QC monitoring (software-driven) will augment long-run stability and laboratory compliance for high-throughput monitoring programs.
• Expansion of partial-extraction workflows (no-HF) coupled with improved plasma robustness will support routine surveillance and screening where total SiO2 decomposition is not essential.

Conclusion

The combination of the Agilent 9500 ICP-QQQ (with UHMI and Dual-Cell System), the Mira Mist nebulizer and an in-line 120 µm particle filter provides a robust, high-sensitivity approach for multi-element analysis of soil and sediment digests following EPA 6020B principles. The configuration delivered low ppt-level LODs, equivalent washout behavior to standard setups, sustained stability over long runs, and reliable recoveries for CRMs and spiked samples—all while reducing the need for pre-analysis filtration and lowering the risk of sample-introduction blockages. This approach supports increased laboratory throughput and operational resilience for environmental testing laboratories.

Reference

1. U.S. EPA. 2014. Method 6020B (SW-846): Inductively Coupled Plasma-Mass Spectrometry, Revision 2.
2. Kubota, T. Fast and Reliable Analysis of Soil and Sediments using ICP-MS with an Innovative Cell. Agilent publication, 5994-9128EN.
3. Dual-Cell System (DCS) and Advanced Helium Mode (AHM). Agilent publication, 5994-8985EN.
4. Air Cell Mode of Agilent 9500 ICP-QQQ with Dual-Cell System. Agilent publication, 5994-8987EN.
5. Sugiyama, N. Solving Doubly Charged Ion Interferences using an Agilent 8900 ICP-QQQ. Agilent publication, 5994-1155EN.