Agilent ICP-MS Journal (March 2006 – Issue 26)

Importance of the Topic

Accurate and traceable measurement of elemental concentrations and chemical species is critical for regulatory enforcement, international trade, environmental protection and clinical diagnostics. Establishing chemical metrology and robust speciation analysis ensures data comparability between laboratories worldwide and underpins reliable decision making.

Objectives and Overview

• Develop and validate reference methods based on ICP-MS and isotope dilution mass spectrometry (IDMS) to achieve traceable chemical measurements and support the Mutual Recognition Arrangement (MRA).
• Apply approximate matching and double IDMS protocols to minimize bias and uncertainty for challenging analytes such as tributyltin (TBT) in sediments and selenium in biological matrices.
• Establish a dedicated ICP-MS facility at LCABIE for advanced speciation analysis across environmental, food and clinical disciplines, including capillary and nano-LC, GC coupling and laser ablation techniques.

Methodology and Instrumentation

The reference methods employ species-specific IDMS with enriched isotopic spikes, accelerated solvent extraction (ASE) for sediment samples, and chromatographic separation by HPLC or GC prior to measurement on Agilent 7500 series ICP-MS platforms equipped with collision/reaction cell technology. Key parameters include optimized CRC gas flows to remove polyatomic interferences, double IDMS calibration against natural standards, and sheathless interfaces for capillary and nano-LC with total sample uptake below 500 nanoliters per minute. Laser ablation-ICP-MS is used for in-gel localization of metalloproteins.

Main Results and Discussion

• In CCQM key comparisons, the LGC TBT reference value of 1.046 nmol/g in sediment and selenium value of 7.04 mmol/kg in salmon showed excellent agreement with global NMIs, with expanded uncertainties (k=2) of 0.093 nmol/g and 0.034 mmol/kg respectively.
• Collision/reaction cell optimization reduced argon dimer interferences for selenium, achieving detection limits as low as 4–6 ng/L in aqueous solutions.
• LCABIE implementations yielded absolute detection limits for selenium as low as 25 fg using nano-HPLC interfaces and enabled reliable speciation of arsenic, mercury and tin species in complex matrices.

Benefits and Practical Applications

Traceable ICP-MS methods with isotope dilution deliver minimal bias and low uncertainty, critical for certification of reference materials, proficiency testing, quality assurance and regulatory compliance. Speciation data provide insights into bioavailability, toxicity and environmental fate of trace elements and organometallic compounds.

Future Trends and Possibilities

• Further miniaturization of separation techniques for single-cell and limited-sample analyses.
• Development of advanced collision and reaction chemistries to address emerging isobaric interferences.
• Expansion of key comparisons and global networks for harmonized certified reference materials.
• Integration of hyphenated ICP-MS with lab-on-chip and multidimensional chromatography for comprehensive speciation profiling.

Conclusion

The combination of ICP-MS with isotope dilution and tailored hyphenated interfaces provides a powerful foundation for chemical metrology and speciation analysis. Ongoing collaboration through CCQM and continuous methodological advances ensure reliable, globally comparable data for diverse applications.

Used Instrumentation

• Agilent 7500a, 7500i, 7500c, 7500ce and 7500cs ICP-MS systems with collision/reaction cell
• Agilent 1100 HPLC with C18 and specialized stationary phases
• GC-ICP-MS interfaces and accelerated solvent extraction equipment
• Sheathless capillary and nano-HPLC nebulizers and transfer lines
• Laser ablation modules coupled to ICP-MS

References

1. Sargent M Traceability in chemical analysis In Encyclopaedia of Analytical Science Ed P Worsfold Academic Press 2005 477–485
2. CIPM CCQM Collaborative programme for chemical metrology Metrologia 1993
3. Sargent M The UK Chemical Calibration Facility The VAM Bulletin 2002 27 18–22
4. Sargent M Metrology in chemistry J Anal At Spectrom 2005 20 1017–1018
5. Sargent M Harte R Harrington C Guidelines for achieving high accuracy in IDMS RSC 2002
6. Wahlen R Wolff-Briche C Comparison of GC-ICP-MS and HPLC-ICP-MS for TBT analysis Anal Bioanal Chem 2003 377 140–148
7. Bueno M Pannier F Trace element speciation using ICP-MS collision cell techniques Anal Chem 2005 20 88–94
8. Anonymous Gel electrophoresis LA-ICP-MS mapping of selenoproteins Unpublished LCABIE results
9. Anonymous Isotopic dilution for volatile organometal quantification by GC-ICP-MS Anal Chem 2006 78 965–971