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 from nuclear activities and poses environmental and health concerns. Accurate, sensitive measurement of 129I/127I ratios in aqueous samples is essential for monitoring nuclear emissions, assessing contamination pathways and supporting regulatory compliance.

Objectives and Study Overview

The study aimed to develop and validate a rapid, direct ICP-MS method employing a high-energy oxygen collision/reaction cell (CRC) to quantify ultratrace levels of iodine-129 and achieve a measurable 129I/127I ratio down to 1×10-7 in aqueous matrices without additional sample preparation. Calibration and performance were assessed using NIST SRM 3231 materials at levels I (1×10-6), laboratory-modified intermediate (1×10-7) and level II (1×10-8).

Methodology and Instrumentation

• ICP-MS platform: Agilent 7700x equipped with 3rd generation Octopole Reaction System (ORS3).
• CRC gas scheme: Oxygen cell gas for charge-transfer removal of 129Xe+ background and helium for kinetic energy discrimination and thermalizing I+ ions.
• Optimization: Oxygen flow varied up to 1.12 mL/min; optimum at 90 % flow (≈1.0 mL/min) to minimize background equivalent concentration (BEC) for 129I (0.6 ng/L).
• Calibration: External calibration using NIST SRM dilutions in 0.5 % TMAH alkaline solution, covering 127I and 129I linear ranges.
• Interferences addressed: Reduction of 129Xe+, suppression of 127IH2+ polyatomics; subtraction of residual 127IH2+ when necessary.

Instrumental Setup

• RF power 1550 W; sampling depth 8 mm; carrier gas 1.05 L/min.
• Spray introduction: Micromist concentric glass nebulizer; Scott double-pass quartz chamber at 2 °C.
• ORS3 conditions: Cell entrance –130 V; exit –140 V; He flow 4 mL/min; O2 at 90 % of max; kinetic energy discrimination mode.

Results and Discussion

• Calibration curves for 127I and 129I exhibited excellent linearity; BECs were 0.65 µg/L (127I) and 1.9 ng/L (129I).
• Detection limits (3σ, n=10): 0.14 µg/L for 127I; 1.1 ng/L for 129I.
• NIST SRM Level I (certified 0.981×10-6): measured ratio matched within certificate uncertainty after blank subtraction.
• Lab-modified intermediate (expected 1×10-7): average ratios around 1.03×10-7 with RSD ~5–15 % across replicates.
• NIST SRM Level II (0.982×10-8): achieved reliable measurement at c.a.1×10-8 with RSD <10 %.

Practical Benefits and Applications

The developed method allows fast, direct quantification of both stable and radioactive iodine isotopes in water. Its simplicity and sensitivity make it suitable for routine environmental monitoring around nuclear facilities, QA/QC in radiochemical workflows and emergency response sampling.

Future Trends and Opportunities

• Integration with online sample introduction systems for real-time monitoring of iodine isotopes in effluents.
• Exploration of alternative reactive gases or mixed-gas CRC modes to further reduce background and enhance sensitivity.
• Extension to speciation analysis coupling chromatographic separation with high-energy cell techniques.
• Application to solid or biological matrices adopting micro-digestion or laser ablation approaches.

Conclusion

The high-energy oxygen CRC ICP-MS method meets the objective of measuring 129I/127I down to 1×10-7 in aqueous samples with detection limits at the sub-nanogram per liter level. The approach is robust, accurate and readily adoptable for routine ultratrace iodine isotope analysis.

Reference

• 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, PC-330; 2011.