Small amounts of chloride ion have been determined spectrophotometrically by means of iron(III) alum (NH4Fe(S04)2• 12H20) reagent solution in nitric acid and thiocyanate reagent solution in methanol. Previously developed methods using iron(III) alum and thiocyanate for determining chloride ion are not sensitive enough and/ or have non-linear calibration curves. Therefore, attempts to improve these methods were made in the present work. The results are as follows. Higher linearity and better

more »

... itivity of calibration curves were obtained with higher concentrations of iron-(III) alum (150 -300 g/dm3 in 6 M HN03, 2 ml) and mercury thiocyanate reagents (9 g/ dm3 in McOH, 2 ml, or 4 g/ dm3 in McOH, 4 ml) in the chloride ion concentration of up to 20 mg/ dm3. The influence of light on absorbance of the solution was very small, although the temperature dependence on absorbance was relatively great. Effects of nitric acid concentration and stirring conditions were also studied.