Potentiometric/flow-injection determination of trace hydrazine and its application to boiler water

A simple and rapid potentiometric FIA method for the determination of trace hydrazine is developed, using a combination of a Ce(IV)-Ce(III) potential buffer solution and a flow-through type redox detector. The method is based on the measurement of the transient potential change from the equilibrium potential governed by the Ce(IV)/Ce(III) couple in the potential buffer to the lower potential governed by the N₂H₅⁺/N₂ couple, which was estimated by spectrophotometric and potentiometric batch experiments. In the present method, the sample (200 μl) is injected into a water carrier stream and merged with the potential buffer stream consisting of acidic Ce(IV)-Ce(III). The concentration of hydrazine is determined by measuring the potential change with the potentiometric detector constructed with a Pt-electrode and an Ag/AgCl reference electrode. Hydrazine in a wide range from 10^-7 M to 10^-3 M can be determined by selecting the concentration of potential buffer solution from 10^-4 M to 10^-2 M. The linear relationship between peak heights and concentrations of hydrazine from 5 × 10^-7M to 5 × 10^-6 M and the lower detection limit of 1 × 10^-7M (3.2 ppb) were obtained when a 2 × 10^-4M Ce(IV)-Ce(III) buffer was used. The relative standard deviation was 0.9% (n=6) for analysis of 5 × 10^-6M hydrazine at sampling rates of 40h^-1. The present method was applied to the determination of hydrazine in real boiler water, and was found to provide a good recovery for boiler water containing hydrazine at the 10 ppb level.