Determination of Iodide in Seawater and Other Saline Matrices Using a Reagent-Free Ion Chromatography System with Suppressed Conductivity and UV Detections

Significance of Topic

The determination of iodide in seawater and saline samples is critical for nutrition studies, environmental monitoring and quality control of iodized products. High chloride, carbonate and sulfate levels in marine matrices pose analytical challenges that require selective and sensitive techniques.

Objectives and Overview

This study presents a reagent-free ion chromatography method using an IonPac AS20 column with suppressed conductivity and UV detection to quantify iodide in seawater, synthetic sea salt and iodized table salt without sample pretreatment. Linearity, detection limits, precision and accuracy were evaluated.

Used Instrumentation

• Dionex ICS-3000 RFIC-EG system with SP pump or DP pump, EG eluent generator and DC detector module
• AS autosampler and ICS-3000 VWD UV-vis detector with semi-micro PEEK flow cell
• EluGen EGC II KOH cartridge with CR-ATC II trap column
• IonPac AG20 guard column and AS20 analytical column (2 mm)
• Chromeleon 6.8 chromatography data system

Methodology and Procedures

An electrolytically generated KOH eluent (13–45 mM gradient) was delivered at 0.25 mL/min and the column maintained at 30 °C. A 10 µL injection volume was split between suppressed conductivity detection (ASRS 300 in external water mode) and UV absorbance at 223 nm. Simulated seawater, commercial sea salt and iodized salt samples were prepared by dissolution, filtration and spiking with known iodide concentrations. Calibration standards ranged from 10 to 250 µg/L iodide.

Main Results and Discussion

The AS20 column provided high capacity and resolution of iodide from high-matrix anions with retention near 19.4 min. UV detection selectively measured iodide without interference from major anions, whereas conductivity detection suffered peak overlap. Calibration was linear (r2>0.996), with limits of detection ~15 µg/L and quantitation ~50 µg/L. Precision was <1.7% RSD for peak areas. Recoveries in diverse saline matrices ranged from 94% to 103%.

Benefits and Practical Applications

This method allows direct analysis of saline samples without dilution or pretreatment, reduces reagent handling through on-line eluent generation, and employs UV detection for improved selectivity. The use of 2 mm columns minimizes waste and operational cost, making it suitable for routine environmental and quality control laboratories.

Future Trends and Potential Uses

Advances may include coupling with mass spectrometry for speciation of iodine species, integration into automated monitoring systems for coastal studies, and adapting the approach for other trace anions in high-salt matrices. Emerging suppressor technologies and microflow chromatography could further enhance sensitivity and throughput.

Conclusion

The reagent-free ion chromatography method using the IonPac AS20 column with suppressed conductivity and UV detection provides a robust, accurate and efficient solution for iodide determination in saline matrices. It delivers high selectivity, low detection limits and simplified operation for diverse analytical applications.

References

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