Agilent ICP-MS Journal (April 2008 – Issue 34)

Importance of the Topic

The analysis of samples with high total dissolved solids (TDS), such as aqua regia soil digests or high-purity metal solutions, presents major challenges for conventional ICP-MS methods. Excessive dilution adds time, risk of contamination and cost, while aggressive acid matrices can damage interfaces and suppress signals. The High Matrix Introduction (HMI) accessory for the Agilent 7500cx ICP-MS addresses these issues by providing aerosol dilution in the plasma, enabling direct introduction of solutions with TDS >1% and high acid content. This capability streamlines workflows, maintains sensitivity and supports regulatory compliance in environmental, industrial and high-tech laboratories.

Objectives and Overview

This work had two primary aims:

• Evaluate the performance of the Agilent 7500cx ICP-MS fitted with HMI for direct analysis of undiluted aqua regia soil digests in compliance with Dutch regulation AS3000.
• Demonstrate improved method detection limits (MDLs) and practical benefits when analyzing high-matrix environmental samples and trace contaminants in high-purity metals without prior dilution.

Studies included calculation of MDLs, long-term robustness testing over a 23-hour sequence, continuing calibration verification, and recovery of certified reference materials in aluminum and copper.

Methodology

Soil samples (1 g) were digested with 8 mL aqua regia in a microwave system and brought to 50 mL with ultrapure water (4% HNO₃, 12% HCl). MDLs were determined as three times the standard deviation of low-level spikes (10 replicates same day and 10 replicates over 30 days). A 23-hour, 235-sample sequence (plus calibrations and CCVs) assessed drift and calibration stability. High-purity metal CRMs (JSAC 0121 Al and NIST 3982 Cu) were dissolved in 20% aqua regia or 10% HNO₃ and analyzed directly. MDLs and recoveries were compared to conventional 1:10 dilutions where applicable.

Instrumentation

• Agilent 7500cx Octopole Reaction System ICP-MS equipped with High Matrix Introduction (HMI) accessory
• Burgener MiraMist PFA nebulizer
• ORS collision/reaction cell: He collision gas for most analytes; H₂ reaction gas for Se
• Agilent ICP-MS ChemStation software rev. B.03.07 with HMI interface controls and 21 CFR Part 11 user access options
• Microwave digester for soil aqua regia extraction

Major Results and Discussion

MDLs for regulated elements in soil digests were typically an order of magnitude lower than Dutch AS3000 limits (e.g., Cr: 2.3 mg/kg MDL vs. 15 mg/kg requirement). Over 23 hours, internal standard drift was about 20%, fully corrected by online internal standards. Continuing calibration check samples remained within ±10% limits throughout 235 soil analyses. Average per-sample analysis time including He and H₂ mode acquisitions was 5.9 minutes, matching conventional methods but without dilution overhead. In comparative tests on spiked soils, HMI yielded equal or slightly improved MDLs versus a 1/10 dilution approach and maintained precision and accuracy in LCS/MS/MSD QC samples. For high-purity metals, recoveries of CRM values ranged from 97% to 114%, demonstrating accurate trace contaminant determination in 10–20% acid matrices.

Benefits and Practical Applications

• Speed: eliminates manual or online dilution steps; compatible with intelligent rinse functions;
• Productivity: same sample-to-sample time as conventional runs, with total run-time savings from omitted prep;
• Robustness: stable operation over extended sequences without cone deterioration or sensitivity loss;
• Cost savings: reduced reagent use, consumable wear and labor; consolidation of multiple instruments into a single ICP-MS platform;
• Regulatory compliance: meets environmental method requirements (EPA 6020A, AS3000) and supports QA/QC standards.

Future Trends and Potential Uses

Adoption of HMI is expected to expand to clinical, forensic and life-science applications, including direct analysis of biological digests and tissue ablation aerosols. Integration with GC/LC ChemStation and Enterprise Content Management systems will streamline hyphenated analyses and 21 CFR 11 compliance. Advances in collision/reaction cell technology, real-time aerosol dilution control and software automation will further enhance matrix tolerance, lower detection limits and support imaging or speciation studies. The ongoing development of reference material databases will aid method validation across diverse sample types.

Conclusion

The Agilent 7500cx ICP-MS equipped with the High Matrix Introduction accessory provides a robust, sensitive and user-friendly solution for direct analysis of high-TDS and high-acid samples. By eliminating dilution steps, the HMI dramatically improves throughput, reduces contamination risk and lowers operating costs, while maintaining or enhancing method detection limits and regulatory compliance.

References

• Agilent Application Note: Direct Analysis of Undiluted Soil Digests Using the Agilent High Matrix Introduction Accessory with the 7500cx ICP-MS, 5989-7929EN
• Agilent Application Note: Using the Agilent 7500cx ICP-MS with High Matrix Introduction Accessory for Analysis of Metals in High Tech Manufacturing, 5989-8095EN
• Agilent Application Note: Agilent ICP-MS ChemStation – Complying with 21 CFR Part 11, 5989-4850EN
• International Atomic Energy Agency: Database of Natural Matrix Reference Materials (IAEA NMRM)