Abstract
Chloride, bromide or iodide ions react with solid silver iodate to liberate iodate ions with the precipitation of silver halide. Triiodide ions are formed by adding potassium iodide and acetic acid to the solution of iodate ion. The present paper deals with a spectrophotometric method for the determination of halide ion based on the measurement of the absorbance of triiodide ions thus formed. The analytical procedure is as follows: Five milliliters of a sample solution containing (0.23.0) × 10-4 M halide ion, 1 ml of 1 M acetic acid and 5 ml of ethanol are added to a centrifuge tube with a stopper, and mixed. After the tube has been allowed to stand in a water bath at 20 °C for about 10 min, 20 mg of silver iodate is added. The mixture is shaken for 3 min and then centrifuged for 3 min at about 3000 rpm. One milliliter of the supernatant solution is transferred to a glass tube with a glass stopper. Then, 7 ml of water, 1 ml of 1 M potassium iodide and 1 ml of 1 M acetic acid are added to the supernatant solution. The absorbance is measured within 10 min at 350 nm with a 10 mm quartz cell against water. For the individual determination in the presence of other halide ions, a suitable separation procedure has been required before this method is applied. The chloride ion in natural waters can be satisfactorily determined by this method, because bromide or iodide ions are not usually present in these samples in such concentrations as would give a serious error. The coefficient of variation of the determination was found to be 1.9 % from 10 repeated measurements with 5.5 × 10-4 M of chloride ion in a town water sample.
