Investigation of the iodine species is important to better understand the sources and mobilization processes of high- iodine groundwater. A fast and sensitive method for the deter- mination of iodate (IO3–) and iodide (I–) in groundwater using an improved ion chromatogra- phy method coupled with induc- tively coupled plasma mass spectrometry (IC-ICP-MS) is described. To shorten the sepa- ration time of iodine species, a short anion-exchange column, Dionex AG-19, was examined as the analytical column. Isocratic elution using 30 mM KOH facili- tated the chromatographic sepa- ration of IO3– and I– within one minute, reducing the time in comparison to previous IC-ICP- MS methods with conventional long IC columns (i.e., Hamilton X-100 or Dionex AS-16) by 90%. Moreover, the low analytical sensitivity of iodine, due to its high ionization potential (10.08 eV), was improved five-fold by addition of small amounts of CH4 to the Ar plasma. The detection limit was 0.005 μg L–1 for IO3– and 0.006 μg L–1 for I–, while the relative standard deviation for five injections of 0.2 μg L–1 I– or IO3– was 1.2–3.3%. The analyti- cal results for three water stan- dard reference materials were in agreement with the certified values. The proposed method was successfully applied to the determination of I– and IO3– in seven shallow groundwater sam- ples collected from the Datong Basin, Northern China. The dis- tributions of the iodine species, differing from mountain front plains to flat alluvial plain regions, indicate that the mobi- lization process of iodine is asso- ciated with complex redox conditions.