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A method for the spectrophotometric determination of cobalt, based on the formation of a coloured chelate (Amax. 480 nm, emax, 2.83 x lo4 1 mol-l cm-l and colour contrast 134 nm) with benzyl 2-pyridyl ketone 2-pyridylhydrazone, is described. Under the optimum conditions, colour development is instantaneous and the colour is stable for several weeks. Under appropriate working conditions, the method is applicable to the determination of cobalt in manufactured paints and environmental samples of paint. The fundamental solution chemistry of the reagcnt and a. brief description of its more interesting colour reactions are also reported.Keywords ; Benzyl 2 -p y ~i d y l ketone 2-pyridyllaydvazone reagent ; cobalt determination ; paint analysis ; spectvophotonzetry Many methods have been developed for the spectrophotometric determination of cohalt,l but these 1iaL.c not been applicable to paints. Cobalt compounds are reported to be t o x i ~, ~-~ cau4ng health disorders through ingestion, inhalation and skin contact ; some threshold limit \ d u e s (TLJ7s) for environmental cohaltj are 0.1 mg m-3 (USA), 0.5 mg m-3 (Germany) and 0 . 1 mg ni-3 (Sweden). As the prescnce of paint mists in industrial workroom environments often causes thcse TLI's t o be exceedcd, cobalt levels must be checked periodically; therefore, ~netliods for its determination in paint are needed. Benzyl 2-pyridyl ketone 2-pyridylliydrazone (BPKPH) has been reported recently as being a highly scnsitil-e reagent for the fluorinietric determination of galliumj6 zinc7 and cadmium.* In this paper the fundamental solution cliernistry of the BPKPH and a superficial description of its more interesting colour reactions, reported in detail el~ewliere,~ are given. The results sliow that BPKPH is a promising reagent for the spectrophotometric determination of metal ions. A rapid, simple and selective spectrophotometric method for the determination of cobalt in paints and environmental samples of paint is described here. The method demonstrates the reliability and versatility of the reagent for such purposes and presents an alternative to atomic-absorption spectrometry,1° having a similar sensitivity. Experimental ReagentsThe synthesis of BPKPH has been reported previously.6 Solutions (1 x 10-3 11) were prepared weekly by dissolving 0.028 8 g of BPKPH in 100 ml of absolute ethanol (Merck, analytical-reagent grade).A stock solution containing 6.904 g 1-1 of cobalt, complexometrically contrasted, was prepared from cobalt (I I) nitrate hexahydrate (UCB, analytical-reagent grade). \Vorking solutions were prepared by appropriate dilution of the stock solution.Bemy1 2-pyridyl ketone 2-pyridyllzydrazone. CobnZt solzition.Acetate b u f e r solzition, p H 4.0, 0.5 31. Jlnskiirg solzition. A solution 1 M in sodium thiosulphate, 0.13 31 in sodium citrate and 1.5 JI in ammonium fluoride was prepared in de-ionised, distilled water from analyticalreagent grade reagents. ApparatusThe following apparatus was used: a Beckman Acta I11 spectrophotometer; a Beckman, ~I o d c l IIRGT, ...

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The synthesis, characteristics and analytical applications of pyridine-2aldehyde 2-furoylhydrazone (PAFH) are described. This compound has been examined to evaluate its usefulness as a selective and sensitive spectrofluorimetric reagent for gallium. The method is applied in 0.8% ethanolic solution a t p H 4.5. Under these conditions the fluorescent species have excitation and emission maxima at 380 and 445 nm, respectively. The detection limit is 0.8 ng ml-1 and the range of application is between 1 and 50 ng ml-l. The method has been employed to determine gallium in synthetic mixtures and its recovery from human urine samples.