On-line isotope dilution analysis with the 7700 Series ICP-MS: Analysis of trace elements in high matrix samples

Significance of the Topic

The reliable determination of trace elements in high-matrix samples (such as seawater, wastewater, urine, and sludge) is critical for environmental monitoring, food safety, and quality control. Complex matrices and high dissolved solids often lead to polyatomic interferences, signal drift, and frequent recalibrations, undermining data accuracy and throughput.

Study Objectives and Overview

This application note presents a streamlined on-line isotope dilution analysis (OIDA) method coupled with an Agilent 7700x ICP-MS operating in helium collision mode and equipped with High Matrix Introduction (HMI). The goals are to:

• Eliminate time-consuming external calibrations and sample preparations.
• Correct for matrix suppression and signal drift automatically.
• Extend dynamic range and improve accuracy and precision across a wide concentration span.

Methodology and Instrumentation

The analytical setup comprises an Agilent 7700x ICP-MS with a third-generation Octopole Reaction System (ORS3) in helium collision mode for interference removal, and HMI for direct analysis of samples up to several percent total dissolved solids. Key components include:

• MicroMist nebulizer and cooled double-pass spray chamber.
• Quartz torch with 2.5 mm injector.
• On-line internal standard addition kit to deliver a multielement isotopically-enriched spike (IES-WAK) via dual-channel peristaltic pump.
• Synthetic and certified reference materials (NASS-5, SPS-WW1, NIST 2670a, BCR-146R) used to validate accuracy.

Main Results and Discussion

The OIDA method achieved a quantification range spanning over four orders of magnitude (0.1–1000 µg/L) with limits as low as 0.1 µg/L. Recoveries for spiked seawater fell between 90 % and 104 % across regulated elements, while certified reference materials yielded results within their stated uncertainties. The approach effectively corrected matrix effects and drift without reagent-based calibration, maintaining precision (RSD < 5 %) and reducing analysis time to approximately 2.5 minutes per sample.

Benefits and Practical Applications

This methodology offers:

• Absolute quantification traceable to primary isotopic standards.
• Automated on-line spiking, eliminating manual dilution and calibration.
• Robust interference removal for both primary and confirmatory isotopes.
• High sample throughput with minimal downtime.
• Applicability to regulatory testing, environmental monitoring, and industrial QA/QC.

Future Trends and Potential Applications

Emerging directions include:

• Development of tailored multielement isotopic spikes for specialized matrices.
• Integration with automated sample preparation systems.
• Expansion of on-line dilution strategies for even higher matrix loads.
• Application to emerging contaminants and high-throughput screening in pharmaceutical and food industries.

Conclusion

The combination of OIDA with ORS-ICP-MS in helium collision mode and HMI delivers a robust, accurate, and high-throughput solution for trace element analysis in challenging high-matrix samples. The method simplifies workflow, enhances data quality, and reduces operational costs, making it ideal for both routine and research laboratories.

References

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2. J. Vogel and W. Pritzkow, J. Metrol. Soc. India, 25(3) (2010) 135.
3. G. Centineo and J.A. Rodríguez Castrillón, On-line Isotope Dilution Analysis ICP-MS: Technical Overview, ISC-Science (2011).
4. S. Wilbur and C. Jones, Agilent application note 5990-5514EN (2009).
5. J.I. García Alonso, Anal. Chim. Acta, 312 (1995) 57.