COMPLEXING PROPERTIES OF URANIUM AND LANTHANOIDS WITH 4-(2-THIAZOLYLAZO)-6-CHLORORESORCINOL

4-(2-Thiazolylazo)-6-chlororesorcinol(TAR-Cl) reacts sensitively with uranyl(II) and lanthanoids(III), and forms: reddish-brown 1:1 and 1:2 complexes. The complexing behaviors were examined spectrophotometrical ly. The absorption maxima of the complexes are focused near 553 nm and the optimum pH for complexation lies between 6.5-8.8. Beer's law hold s up to about 2 x 10(-5) mol l(-1), with a molar absorptivity of 3.00 X 10(4) l mol(-1) for uranium and 6 X 10(4) l mol(-1) cm level for eac h lanthanoid. The absorptivities are increased with the atomic number, especially in light lanthanoids, that are correlative both to the lan thanoid contraction and the basicity of ortho hydroxyl group in the re sorcinol ring, but such effects are not clearly recognized in heavy la nthanoids. Effect of masking agents was also examined, and uranium cou ld be determined selectively in the presence of lanthanoid mixtures by the addition of CyDTA.