Laser thermal lens spectrometric determination of rhodium by the new chromogenic reagent 5-bromo-(2-thiazolylazo)-5-diethylaminobenzoic acid

A highly sensitive method for determination of rhodium by laser thermal lens spectrometry based on the colour reaction between rhodium and the new chromogenic reagent 5-bromo-(2-thiazolylazo)-5-diethylaminobenzoic acid (5-Br-TADEB) has been developed. The experimental results show that in a acetic acid-sodium acetate buffer solution of pH 4.0-5.7 and in the presence of acetone, rhodium reacts with 5-Br-TADEB to form a 1:2 stable blue complex exhibiting an absorption maximum at 632 nm which is well-matched to the wavelength of the laser beam used (λ=632.8 nm). The detection limit and linear range of rhodium(III) are 0.004 μg mL^-1 and 0.01-0.08 μg mL^-1, respectively. The method has also been applied to determine rhodium in catalyst samples with satisfactory results.