Method for the determination of broad concentration range of iodide in drinking water by spectrophotometry with alkaline potassium permanganate oxidation

Objective To establish a simple photometric method for the determination of broad concentration range of iodide in drinking water. Methods Iodide in water was oxidized with potassium permanganate in alkaline medium to generate iodate. After excessive oxidant was eliminated with nitrite sodium in acidic medium condition and excessive nitrite was eliminated with a mixture of aminosulfonic acid and urea, iodate was used to react with potassium iodide reagent to form I_2 which further reacted with amylum to form color complex. The absorbance was determined by photometry. In determination reagent system suitable amount of iodide that acted as background and sodium chloride were added to solve the problem of the chromogenic sensitivity, i.e., when iodine concentration was < 100 μg/L in water sample the degree of iodine-starch complex color change could not be in linear proportion to the concentration of iodine in water. Results The linear range of the calibration curve of the new method for iodine was 0-1200 μg/L and the linear correlative coefficient was 0.9998. The detection limit for iodine was 4 μg/L. Results of 6 times repeated determination of water samples with iodine concentration of 76.6, 207.8, 560.4 μg/L showed that the relative standard deviations(RSD) were all under 1%. The recovery of standard addition for iodine added in 8 water samples of different iodide concentration levels was 97.0% (485.2/500.0) - 102.5% (102.5/100.0). Interference of hexavalent chromium(Cr~(6+)) in water was eliminated when treated with ferrous reagent. Interference of bromate (BrO_3~-) in water was eliminated when treated with potassium bromide and nitrite sodium reagent. Zero point two mg/L Cr~(6+), 0.1 mg/L BrO_3~- in water were noninterference. Conclusion This method can be easily performed with good precision and accuracy and has broad detection concentration range, which is suitable for measuring iodide in drinking water. Key words: Iodides;  Water;  Spectrophotometry