Differential Determination of Hydrazine and Hydroxylamine in Mixtures by Amperometric Titration Utilizing the Difference in Reaction Rates

Abstract

An amperometric titration measuring the reduction current of iodate ions for the differential determination of H₂N4.2 HCl and NH₂OHCl in mixtures has been studied with a rotating platinum electrode (2000 rpm) at the potential of +O.6 V vs. SCE. The method is based on the difference in their reaction rates with potassium iodate in the presence of hydrochloric acid and sodium chloride. N2H4.2 HCl in the mixture was titrated with potassium iodate prior to NH₂OHCl, while the latter was titrated after the addition of potassium bromide.
A series of mixtures containing between 0.2, umol to 200, umol of N21-14HCl and 2pmol to 200, umol of NH₂OHCl was determined by the following two methods. The recommended procedures were as follows.
( 1 ) Successive determination: An equimolar mixture (ca.20 pmol each) containing N2H4.2HCl and NH₂OHCl was introduced into the titration cell, and hydrochloric acid (6molg, 8 m1) and water were added to make the total volume up to 30m1. After the solution was saturated with sodium chloride (18g) at 45° C, N2H4.2HCl was titrated with 0.05m1 portions of 0.01 molf/ potassium iodate at intervals of 5sec (O.05 m//5sec). Then NH₂OHCl was suc- cessively titrated with O.01 mol/l potassium iodate (O.05 ml/20 sec) at 45° C after potassium bromide (4 mol//, 4.5m1) and water (25m1) were added. Mixtures containing N2-4..2 HCl and NH₂OHHCl, of which molar ratios were 1: 1 (20 pmol each) to 1: 8 (5, umol of N2H4.2HCl: 40pmol of NH₂OHCl), were analysed with the relative error less than O.3%. Time required for titration was about 15 minutes.
( 2 ) Differential determination: An equimolar mixture (ca.20, umol each) containing N21-142HCl and NH₂OHCl was analysed by using two aliquots. One aliquot was used to titrate N2H4.2HCl with 0.01 mol// potassium iodate (0.05 ml/5sec) at room temperature after the addi- tion of hydrochloric acid (6 mol//, 20m1), sodium chloride (18g) and water to make the total volume up to 50m1. Another aliquot was used to titrate the sum of N2H4.2HCl and NH₂OH. HCl with O.01 mol/l potassium iodate (0.05 ml/20 sec) at 45° C after the addition of hydrochloric acid (6 mol//, 7m1), potassium bromide (4 mol//, 4m1), sodium chloride (18g) and water to make the total volume up to 50m1. The amount of NH₂OHCl was estimated from the difference in the two titrations. Mixtures containing N2H4.2HCl and NH₂OHCl, from 5: 1 (20, umol of N2H4.2HCl: 4 pmol of NH₂OHCl) to 1: 8 (5, urnol of N2H4.2HCl 40, umol of NH₂OH HCl), were analysed with the relative error less than 1%. A mixture of 0.2, umol of N2H4 2HCl and 38pmol of NH₂OHCl was analysed with the relative error of about 2.5%. Total titration time was about 25 minutes. The effects of concomitant compounds were examined.