<p>Monitoring iodine speciation in marine environments holds immense significance due to its profound implications for human health, atmospheric chemistry, and climate regulation. However, conventional methods for determining trace iodine species in seawater are often constrained by complex pretreatment procedures and the challenges posed by the high ionic strength of seawater matrices. In this study, a novel, automated approach that integrates iodine derivatization with headspace solid-phase microextraction (HS-SPME), and is further coupled with gas chromatography-mass spectrometry (GC–MS), for the efficient enrichment and detection of trace iodide and iodate is presented. This method allows for the simultaneous detection of iodide and iodate with a detection limit of 6.4 ng L^− 1 and a quantification range of 0.020–200&#xa0;µg L^− 1. For speciation analysis, iodate is selectively reduced to iodide prior to the derivatization step. The practical viability of this approach was demonstrated through the successful quantification of iodide and iodate in seawater samples collected from the South China Sea. Given its high sensitivity and efficiency, this method presents substantial promise for the ongoing monitoring of iodine in marine environments.</p>