WCPS: Determination of Iodine-129 in Aqueous Environmental Samples by ICP-MS with High Energy Oxygen Collision/Reaction Cell Technique. (PC-330)

Importance of the Topic

Iodine-129 is a long-lived radionuclide released by nuclear activities and requires sensitive analysis for environmental monitoring. Conventional ICP-MS faces challenges from low sensitivity and interferences by 129Xe and polyatomic ions. The development of an oxygen collision/reaction cell technique enables direct ultratrace determination of 129I in aqueous samples.

Objectives and Study Overview

• Achieve a measurable 129I/127I isotope ratio down to 1×10-7 in aqueous media.
• Establish detection limits near 0.01 µg/L for 129I.
• Validate the method using NIST SRM 3231 Level I and II reference materials and laboratory-spiked standards.

Methodology and Instrumentation

• Instrument: Agilent 7700x ICP-MS equipped with the third-generation Octopole Reaction System (ORS3).
• Collision/reaction cell gas: oxygen optimized at 90% of maximum flow (~1.0 mL/min) to remove 129Xe+ via charge transfer (Xe+ + O2 → XeO2+).
• Additional helium gas (4 mL/min) used for kinetic energy discrimination and abundance sensitivity improvement.
• Sample introduction: Micromist concentric nebulizer and double-pass quartz spray chamber cooled to 2 °C.
• Calibration standards: NIST SRM 3231 Level I (129I/127I = 0.981×10-6) and Level II (0.982×10-8), and an intermediate laboratory-prepared standard (1×10-7 ratio) in 0.5% TMAH alkaline solution.

Main Results and Discussion

• Background equivalent concentrations (BEC): 0.65 µg/L for 127I and 1.9 ng/L for 129I at optimized O2 flow.
• Detection limits (3σ, n=10): 0.14 µg/L for 127I and 1.1 ng/L for 129I.
• Calibration curves exhibited excellent linearity for both isotopes across four concentration levels.
• Measured 129I/127I ratios:
  • NIST Level I: 0.981×10-6 (certified value) with RSD <8%.
  • Laboratory-modified 1×10-7 standard: 1.03×10-7 with RSD ~6–13%.
  • NIST Level II: 0.996×10-8 with RSD <8%.
• Mass spectra comparison confirmed significant reduction of 129Xe+ background under high-energy oxygen mode.

Benefits and Practical Applications

• Direct, simple, and rapid analysis of 127I and 129I without complex sample preparation.
• Applicable for routine environmental monitoring of iodine radionuclides in water.
• High throughput potential due to external calibration and minimal blank subtraction.

Future Trends and Applications

• Integration with separation techniques for complex matrices (soil, biota, aerosols).
• Further sensitivity enhancements via advanced reaction gases or tandem mass spectrometry.
• Miniaturized and field-deployable ICP-MS systems for on-site monitoring.
• Application to other radionuclides facing similar interference challenges.

Conclusion

The high-energy oxygen CRC ICP-MS method enables precise determination of ultratrace 129I in aqueous samples with a detection limit near 0.01 µg/L and isotope ratio capability down to 1×10-7. The approach shows reliable performance against certified reference materials and offers a streamlined workflow for environmental surveillance.

References

• Nakano K., Shikamori Y., Sugiyama N., Kakuta S. Determination of Iodine-129 in Aqueous Environmental Samples by ICP-MS with High Energy Oxygen Collision/Reaction Cell Technique. Agilent Technologies Inc., 2011.
• Agilent Technologies. 7700x ICP-MS Operator’s Manual.
• NIST Standard Reference Material 3231, Iodine-129 Isotopic Standard.