In-Vessel Headspace Liquid Phase Microextraction Coupled to Spectrophotometry for Iodate Determination

A new, highly sensitive and selective method for the spectrophotometric determination of iodate is developed based on the in-vessel mode of headspace liquid phase microextraction (IV-HS-LPME). The approach involves converting iodate to vapor iodine with excess of iodide and extracting it into a 50 μL of 1 % potassium iodide, which exposed to the headspace in a specially designed vessel. The extraction proceeds from 8 mL of aqueous solution containing 0.24 mmol L-1 of iodide and 0.5 mol L-1 of Na2SO4 after injection of 2 mL of 25 % H2SO4. The complete equilibrium is established after the aqueous solution stirred at 1200 rpm for 20 minutes. After that, the triiodide complex formed in the acceptor phase is withdrawn with a microsyringe and transferred to a 50 μL quartz micro cell with a 10 mm path length, where the absorbance is measured at 288 or 350 nm. The calibration graph is linear (r2 = 0.9998) in the range of 4 to 180 μg L-1 (as IO3-) with a detection limit of 1.5 μg L-1. The developed method has a high precision of 0.5 – 1.4 %. It was successfully applied to the determination of iodate in table salt, sea, and mineral water samples.