Determination of iodine-containing species in seaweed using IC-ICP-MS

Significance of the topic

Iodine is essential for thyroid hormone synthesis and normal development. Seaweeds accumulate high levels of iodine and can pose risks of excessive intake. Speciation of iodine forms in seaweeds helps assess nutritional value, potential hazards, and informs strategies for reducing total iodine content in food products.

Objectives and study overview

This study aimed to develop and validate a hyphenated ion chromatography–inductively coupled plasma mass spectrometry (IC-ICP-MS) method to quantify inorganic (iodide + iodate) and organic iodine species (3-iodo-l-tyrosine and 3,5-diiodo-l-tyrosine) extracted from various seaweed samples. Four representative matrices were analyzed to evaluate analytical performance and extraction efficiency.

Methodology and instrumentation

Sample preparation employed enzymatic extraction with pancreatin in KH2PO4/NaOH buffer (pH 8), followed by 12 h ultrasonic incubation at 50 °C, cooling, centrifugation, and filtration. Instrumentation included:

• Dionex ICS-6000 ion chromatography with IonPac AG20 and AS20 columns and auto eluent generation (100 mM KOH + 5% MeOH)
• Thermo Scientific iCAP TQ ICP-MS operating in single-quadrupole KED mode with helium collision gas
• ChromControl and Qtegra software for system control and quantification

Key results and discussion

• Optimal separation of IO3−, MIT, I−, and DIT achieved with 100 mM KOH eluent (13 min run time) and 5% methanol for enhanced sensitivity.
• Limits of detection (0.013–0.040 ng mL−1) and quantification (0.043–0.135 ng mL−1) demonstrated high analytical sensitivity.
• Calibration was linear (r² ≥ 0.999) for 0.1–100 ng mL−1 (0.5 ng mL−1 lower bound for DIT).
• Repeatability RSDs were ≤2% for most species; elevated variation (up to 8.3%) observed at low concentrations.
• Spike recoveries ranged from 74% to 121%, confirming method accuracy across different matrices.
• Speciation analysis of four seaweed samples revealed variable extraction recoveries (41–94%), with iodide predominating except in nori, where organoiodine (MIT) constituted a larger fraction.

Benefits and practical applications

This IC-ICP-MS method enables reliable quantification of both inorganic and organic iodine species in complex marine matrices, supporting quality control in food analysis, risk assessment of dietary iodine, and development of processing techniques to modulate iodine levels in seaweed-derived products.

Future trends and applications

Further developments may include optimized multi-enzyme extraction for complete speciation, broader screening of organoiodine compounds, certified reference materials for validated speciation, and application of triple-quadrupole ICP-MS modes to extend analysis to radioactive iodine isotopes and minimize interferences.

Conclusion

The validated IC-ICP-MS workflow provides rapid, sensitive, and accurate determination of key iodine species in seaweed. The approach demonstrates robust performance across diverse samples, offering a valuable tool for nutritional studies, regulatory monitoring, and product standardization.

References

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