The stability constants of the Th(lV) complexes containing Alizarin Maroon (AZM) and as a secondary ligand (L) salicylic acid (SA), 5-sulphosalicylic acid (SSA), 5-nitrosalicylic acid (NSA), 2,2'-bipyridyl (bipy) or 1,lO-phenanthroline (phen) were determined potentiometrically at 25 "C with an ionic strength (1) of 0.1 M (NaC104), and in a 20% WV aqueous ethanol medium.All of these mixed-ligand complexes are more stable than one would expect. The stability of the ternary complexes is discussed in relation to the natures of the secondary ligands involved. The solution spectrum of the complex is characterised by an absorption band with h, , , .at 580 nm within the pH range 4.6-5.5. The ternary system obeys Beer's law between 2.3 and 22.5 yg ml-1 of thorium with a molar absorptivity of 1.1 x 104 I mol-1 cm-1. Finally, a sensitive method has been developed for the micro-determination of thorium based on the formation of the Th -AZM -SSA ternary complex.
Ascorbic acid in pharmaceutical preparations can be determined by either spectrophotometric or titrimetric methods by its reaction with ferricinium trichloroacetate at pH 3. The latter is quantitatively reduced to ferrocene. This is extracted by chloroform and its concentration calculated from the absorbance at 440 nm. Alternatively, an aqueous solution of ascorbic acid is titrated with that of the blue ferricinium salt which acts as an indicator. Vitamins, minerals, hormones, dextrose and coloured additives do not interfere with the reaction. Both methods are simple, rapid and sensitive.
Nickel(II) and Copper(II) chelates of 4-(-thiazolylazo)resorcinol (TAR) were reported. 2T he dissociation constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically and spectrophotometrically at 25 • C, in 50% (v/v) ethanol and 0.1 M ionic strength. The effects of an acid or a base on the visible absorption behaviour of the ligand and complexes has been investigated. Nickel and copper react with 4-(-2t hiazolylazo)resorcinol (TAR) to form a binary complexes. The equilibria occurring in solution were established and the basic characteristics of the complexes formed were determined. The complexation reaction in the systems investigated were demonstrated and characterized using graphical logarithmic analysis of the absorbance versus pH graph. The composition of the formed complexes with the reagent have been determined. The molar absorptivity of the binary system is investigated. The binary systems obeyed beer's law up to 0.23 and 0.25 µg/ml for Ni 2+ and Cu 2+ respectively. A simple and highly sensitive procedure for spectrophotometric determination of Ni 2+ and Cu 2+ has been developed. A method for the simultaneous determination of nickel and copper in mixtures by first-derivative spectrophotometry is described. Zero-crossing measurement technique is found suitable for the simultaneous determination of the metal ions. The method has been applied to direct determination of copper and nickel in dome synthetic mixtures without any separation.
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