Spectrophotometric and analogue derivative spectrophotometric determination of rhodium(III) with 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulphopropylamino)phenol

Abstract

A sensitive spectrophotometric method for the determination of rhodium(III) has been established by reacting rhodium(III) with 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulphopropylamino)phenol (5-Br-PAPS). 5-Br-PAPS reacts with rhodium(III) to form a water-soluble 1 : 2 (metal : ligand) complex on heating at 95 °C. The rhodium(III)-5-Br-PAPS complex has two absorption maxima at 557 and 600 nm in the pH range 4.0–9.2. The molar absorptivity is 1.09 × 10⁵ l mol^–1 cm^–1 at 600 nm. The favourable selectivity of the method is obtained by the addition of EDTA as a masking agent after formation of the rhodium(III)-5-Br-PAPS complex. The sensitivity of the method can be increased about ten times by employing analogue derivative spectrophotometry.