Complexation of lanthanum(III) and terbium(III) with 5-Br-PAAP in the presence of surfactants

The complexation of lanthanum(III) and terbium(III) with 2-(5-bromo-2-pyrid ylazo)-5-diethylaminophenol (5-Br-PAAP) in the presence of surfactants was studied by spectrophotometry. Optimal conditions of interaction and chemica l and analytical characteristics of the resulting complexes were determined . Molar absorptivities are 7.8 x 10(4) (La) and 8.7 x 10(4) (Tb). The effec t of the ionic strength of the solution and concentration of the organic so lvent on the conditions of complexation in the presence of surfactants was considered. Correlation equations relating all chromaticity characteristics to the concentration of lanthanum, terbium, and erbium in the range 5-25 m ug per 25 mL were deduced. it was demonstrated tar the use of the most sens itive chromaticity functions (yellowness, chromaticity coordinates, color s aturation, etc.) increases the sensitivity of the determination by a factor of 25-100 in comparison with the photometric method.