SPECTROPHOTOMETRIC DETERMINATION OF NEODYMIUM IN HIGH-SENSITIVITY CONDITIONS IN ROCKS WITH OMO-2-PYRIDYLAZO)-5-DIETHYLAMINOPHENOL(5-BR-PADAP)

A selective and highly sensitive procedure for spectrophotometric dete rmination of neodymium(III) in rocks has been developed. At pH 10.2 ne odymium(III) reacts with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in a water-ethanol-Triton X-100 medium to form a red-vio let complex which has one absorption maximum, at 580 nm. The molar abs orptivity at 580 nm is 1.64x10(5) l mol(-1) cm(-1). Beer's law is obey ed over a range of 0.044-1.100 mg l(-1) of neodymium. In order to over come the difficulties caused by other ions, an ion exchange chromatogr aphic and liquid-liquid extraction techniques were used. The method ha s been successfully applied to the analysis of synthetic samples and r ock reference materials.