Flow-injection determination of mixtures of amines immobilized in the flow cell of a photometric diode-array detector

A method for the determination of 2,4-dinitrophenylhydrazine and 2- and 4-nitrophenylhydrazine in mixtures based on their different spectral features is proposed. The sample containing the amines is injected into an FIA manifold and passed through the flow cell of a diode-array spectrophotometer where a support (C₁₈ bonded silica) retains the analytes. The amines are concentrated in situ, thereby achieving a determination limit of 5 × 10^?7 M. The carrier (phosphate buffer-methanol) rapidly elutes the retained compounds, so a sampling frequency of 40 h^?1 could be obtained. The resolution of mixtures of these amines can be carried out with acceptable low errors.