Micro Determination of Iodates in the Presence of Periodates and Its Application to the Assay of Hydroxylamine by Amperometric Titration with Potassium lodide

An amperometric titration was developed for the micro determination of iodate in periodate and was applied to the determination of hydroxylamine. The oxidation current of potassium iodide (titrant) was measured at +0.65 V vs. SCE with a rotating platinum electrode (2000rpm) as an indicator current. iodates in the presence of periodates were titrated with potassium iodide at about 10°C after periodates were masked with ammonium molybdate in the presence of hydrochloric acid. Hydroxylamine could be titrated similarly as it reacted with an excess of the periodate to produce the iodate.<BR>The recommended procedures are as follows.<BR>( 1 ) Determination of iodates in the presence of periodates. Both 5 ml of 5 × 10^-4 mol/l potassium iodate and of 10^-2 mol/l periodic acid are introduced into an amber glass titration cell (100 ml), and water is added to make the total voliime up to 50 ml. After 1 ml of 10^-1 mol/lammonium molybdate and 3 ml of 5 mol/l hydrochloric acid are added, the resultant solution is titrated with 10^-2 mol/l potassium iodide at about 10°C. Iodates (4 × 10^-5∼2 ×10^-5mol/l)in the presence of periodates (8 × 10^-6∼5 × 10^-3 mol/l) are determined with relative errors less than 1.4% and coefficients of variation less than 0.2%.<BR>( 2 ) Determination of hydroxylamine hydrochloride. Ten milliliters of 10^-5 mol/l hydroxylamine hydrochloride are introduced into an amber glass titration cell (100 ml). After the pH of the solution are adjusted to 5∼6 with sulfuric acid or sodium hydroxide, 1 ml of 10^-1 mol/l periodate is added, and the solution is boiled gently for 3 minutes. Water is added to make the total volume up to 50 ml and then the reaction mixture is cooled rapidly to about 10°C. After the addition of 1 ml of 10^-1 mol/l ammonium molybdate and 3 ml of 5 mol/l hydrochloric acid, the resultant solution is titrated in the same manner as described in ( 1 ). A blank test is performed through the whole procedure. Hydroxylamine hydrochloride (3∼66, μg) is determined with a relative error and a coefficient of variation less than 0.2%. This method is rapid, simple. precise and especially suitable f or the determination of iodates with no interference of coexisting periodates. t Studies on Analytical Methods by Ampero metric Titration Using a Rotating Platinum Electrode. XLIV.