A new and sharp ternary indicator system for argentometric titration of microamounts of iodide

A ternary indicator system, Cadion 1B-silver ion-emulsifier octylphenyl pol yglycol ether, for visual and direct titration of iodide ion with silver ni trate (as the titrant) is described. The advantages of the method are as fo llows: (1) when the titration reaches the equivalence point, the color of t he resulting solution sharply changes from pure yellow to orange and the so lution remains transparent rather than turbid; (2) the method is sensitive (the detection limit is 2 x 10(-4) mol/L iodide) and accurate (the recoveri es of standard addition are 99.60%-100.8%); (3) the results of titrating io dide by the method agree with those obtained by eosin B as an indicator for iodide; (4) the endpoint is much sharper than that obtained by eosin B as indicator for iodide ion; (5) the method has been successfully applied to d etermination of iodide in the tincture of iodine and tetrapropyl ammonium i odide samples with satisfactory results; (6) a vast amount of iodate, sulph ate and fluoride ions does not interfere; (7) the method also may be automa ted if necessary.