Accurate determination of 129I in environmental samples using triple quadrupole ICP-MS

Significance of the Topic

Accurate measurement of iodine-129 at ultratrace levels is essential for assessing long-term environmental impacts of nuclear reprocessing, weapons testing and reactor accidents. This radionuclide poses health risks due to its long half-life and bioaccumulation in the human thyroid. Enhanced analytical speed and selectivity are required to support regulatory monitoring and rapid response.

Objectives and Overview of the Study

This work evaluates triple quadrupole ICP-MS with oxygen reaction gas for quantifying 129I in aqueous samples. Key goals include removal of isobaric 129Xe and polyatomic interferences from Mo, Sn and natural iodine fragments, comparison with single quadrupole modes, and demonstration of system detection limits and accuracy in simulated environmental matrices.

Methodology

Sample preparation was performed in 0.5% v/v TMAH to minimize memory effects. Calibration standards, blanks and spiked samples contained a matrix of Ca, Mg, Na (20 mg/L), Al, Fe, Mn, Cu (5 mg/L) and potential interferents Mo, Sn (1 mg/L). Oxygen reaction mode was optimized using Reaction Finder and autotune. Single quadrupole (SQ-STD, SQ-KED, SQ-O2) and triple quadrupole (TQ-O2) operational modes were compared. Blank equivalent concentrations (BEC), detection limits (IDL) and spike recoveries were determined.

Used Instrumentation

Thermo Scientific iCAP TQ ICP-MS equipped with Qtegra ISDS software. Daily tuning with mixed standard solution. Typical settings:

• RF power: 1550 W
• Nebulizer gas flow: 1.12 L/min
• Interface: high sensitivity
• QCell O2 gas flow: 0.6 mL/min
• Reaction cell biases: CR -7.2 V; Q3 -12 V
• Intelligent Mass Selection for Q1 optimization

Main Results and Discussion

Oxygen reaction in single quadrupole failed to suppress 127IH2+, MoO2+ and SnO+ interferences, yielding high BEC (2.2 ng/L) and elevated IDL (0.2 ng/L). In TQ mode prefiltering of Mo and Sn eliminated forming product ions, and O2 charge exchange removed 129Xe, reducing BEC to 0.13 ng/L and IDL to 0.001 ng/L.

Interference attenuation factors with TQ-O2:

• 127I spike: signal reduced from 45 to 0.09 ng/L (500× improvement)
• Mo spike: 560 to 0.07 ng/L (8000×)
• Sn spike: 30 to 0.07 ng/L (430×)

Calibration was linear up to 100 ng/L with high correlation. Spike recoveries in simulated matrix ranged from 97% to 105%.

Benefits and Practical Applications

Triple quadrupole ICP-MS in O2 mode delivers rapid, sensitive and selective 129I analysis, reducing reliance on lengthy radiometric methods. The approach is well-suited for environmental monitoring, emergency response, and quality control in nuclear industries.

Future Trends and Opportunities

Potential developments include automated sample handling, coupling with chromatographic separation for speciation, application to other radionuclides and portable TQ-ICP-MS systems for field deployment. Enhanced software for reaction pathway prediction will further streamline method development.

Conclusion

The triple quadrupole ICP-MS approach effectively removes critical interferences and achieves ultralow detection limits for 129I in complex sample matrices. The methodology provides accurate quantification, high throughput and robust performance for environmental and nuclear safety applications.