Flow injection analysis for spectrophotometric determination of trace amounts of hydrazine in boiler feed water

Abstract

Trace amounts of hydrazine in boiler feed water were determined by a flow injectionspectrophotometric method with p-dimethylaminobenzaldehyde (DMBA). The DMBA solution for the color development was prepared by dissolving it in diluted hydrochloric acid without using any organic solvents such as alcohols. The reagent solution proposed in this work had several advantages, compared with the alcoholic solution usually used in the batchwise spectrophotometric method. The solution was easily prepared with hydrochloric acid and water, stable for longer times and did not evolve when the solution was mixed with sample solutions, and the waste treatment was easier than for the alcoholic solution. A carrier (H₂O)and the reagent solution were propelled at flow rates of 1.0 ml min^-1 and 0.6 ml min^-1, respectively. They were merged to flow into a reaction coil (0.6 mm i.d.×6 m) kept in a temperature-controlled air bath at 80°C.Samples were injected into the carrier stream, and the reaction product was measured at 458 nm. Metal ions and ammonia did not interfere with the determination of hydrazine. The calibration graph was linear up to 100 ppb of hydrazine, and the detection limit corresponding to a signal to noise ratio of 3 was 0.2 ppb.Relative standard deviations for seven replicates of 5, 50 and 100 ppb of hydrazine were 1.1, 0.9 and 0.4%, respectively. The proposed method was applied to the determination of hydrazine in boiler feed water samples.