Determination of Iodide in Groundwater by Suppressed Conductance-Ion Chromatography

In an environment without foreign iodine food, the iodine content of water is an important index to measure the iodine intake of the human body, so the accurate determination of iodide content in drinking water has a crucial role in human health. The detection limit of ion chromatography-amperometric detection method is generally lower than that of conductance detection method, and the sensitivity is higher. This method is suitable for the determination of trace iodide in water, but the apparent peak time is later than that of the conductance detection method. Under the same test conditions, for the ion chromatography-hydroxide eluent detection method for the determination of iodide in water, the peak time is obviously better than that of the carbonate body eluent detection method. Using carbonate eluent to analyze iodide requires adding toxic organic improvers, which is complicated, difficult to elute, has a long analysis time, high detection limit and low sensitivity.

IonPac AS23 column with alkanol-based quaternary ammonium functional group has strong hydrophilicity and can maintain high capacity in a wide pH range (0-14), which is suitable for hydroxide and carbonate leaching systems. Based on this, a method for the determination of iodide in groundwater by suppressed conduction-ion chromatography was developed.

IonPac AS23 (4mm×250mm) anion analysis column and IonPac AS23 anion protection column, Dionex AERS 500(4mm) anion inhibited conductivity detector, HPIC separation method, were used to detect iodide in groundwater with 50mmol/L KOH eluent (hydroxide eluent, the product after conductivity inhibition is zero conductivity water, providing an ideal conductivity baseline) at a flow rate of 1.2mL/min (the concentration and flow rate of the eluent increased, and the retention time was shortened) and a suppressive conductance detector current of 125mA (the current increased, the instrument detection sensitivity increased). The sample volume was 250μL, and the samples were filtered through a 0.45μm water microporous filter membrane. 10mL of initial filtrate was discarded, and about 10mL of subsequent filtrate was collected. After that the iodide in the groundwater samples was detected.

The chromatographic peak separation was good, peak shape was symmetrical, and no trailing extension. The iodide peak emerged in 8.980min, the detection limit of the method was 0.5μg/L, the correlation coefficient of the calibration curve was 0.9998, and the linear range was wide (0. 01-2mg/L).

This method has a lower detection limit than that of the existing standard method for the determination of iodide in water, shorter peak time, and the detection range is better than that of the existing ion chromatography method. The experimental results show that the peak time is faster than that reported by its predecessors. This method is used to determine iodide in groundwater and is not disturbed by seven inorganic anions (F^-, Cl^-, NO₃^-, NO₂^-, SO₄^2-, PO₄^3-, Br^-) in water. This method improves the accuracy of the determination of iodide in groundwater by alkanol-based quaternary ammonium functional group column AS23 under the hydroxide eluent system.