Abstract: A new, simple and rapid spectophotometric FI technique for accurate determination of I- has been developed. The method was based on the decrease of absorbance intensity of rhodamine B due to the complexation with [I2Br]-, which I- could be selectively oxidated to form I2 by Ce(Ⅳ) in acidic medium where I2 reacted with Br- to form [I2Br]-. Which I- could be selectively oxidated to form I2 by Ce(IV) in acdic medium where I2 reacted with Br- to form [I2Br]-. At this moment, some changes of the solution’s color took place. It was found useful for sensitivity test in CTMAB media. The absorption peak of the complexation increased linearly by addition of I-, occured at 585nm. Optimization of chemical and FI variables has been made. Under the optimized conditions, the calibration curve obtained was linear over the range 50～1000μg/L, while the detection limit was lower than 20 μg/L, and the precision level ( RSD=0.85%, n=10 ) was found quite satisfactory. This method showed good sensitivity and selectivity. Proper amount of inorganic acid radical ions, metal ions and other halide ions would not interfere the determination. Application of the method to the analysis of I- in kelp, laver, common salt or sea salt would result a good agreement between the expected and found values.

Key words: flow injection, I-, rhodamine B, spectophotometry, kelp, laver