Automated in situ preparation of Azomethine-H and the subsequent determination of boron in fertilizer process and water effluent streams with sequential injection analysis

Abstract

A sequential injection system for the automated in situ preparation of Azomethine-H and the on-line monitoring of boron in water effluents and fertilizer process streams is described. Azomethine-H, a condensation product of salicylaldehyde and H-acid (8-amino-1-naphthol-3,6-disulfonic acid) is used as the chromogenic reagent. The Azomethine-H is prepared in situ by mixing salicylaldehyde and H-acid in the presence of boron. A single bead string reactor is used to promote the mixing process. In solution the chromogenic reagent exists as its two constituents. When boron is added to the solution, Azomethine-H is formed and measured at 420 nm. The proposed system is fully computerised and is able to monitor boron at a rate of 30 samples per hour with a relative standard deviation of <1.4%. The calibration graph is linear up to 100 mg l⁻¹. The system has a detection limit of 0.61 mg l⁻¹.