SPECTROPHOTOMETRIC DETERMINATION OF GALLIUM IN BIOLOGICAL-MATERIALS AT NANOGRAM LEVELS WITH THIOCARBOHYDRAZONE DERIVATIVES

Two spectrophotometric methods for the determination of micrograms of gallium in biological materials are described. Proposed chromogenic reagents are 1-(phenyl-2-pyridyl)carbylidene-5-resorcylidenethiocarbohydrazone (PPRT) and 1-(phenyl-2-pyridyl)carbylidene-5-salicylidene thiocarbohydrazone (PPST), which form yellow 1:2 (gallium: reagent) complexes. Reactions develop at pH 4.5 - 6.0 in a 52% (v/v) DMF solution for PPST and at pH 4.0 - 7.5 in a 48% (v/v) ethanol solution for PPRT. Optimum conditions for reactions are discussed for molar absorptivity values of 59000 and 65000 l.mol-1.cm-1 for PPST and PPRT, respectively. Detection limits are 8 ng/ml for PPST and 5 ng/ml for PPRT, and the range of application is 20-800 ng/ml of gallium. Advantages of the methods include simplicity, high sensitivity and relative selectivity, allowing their application in the determination of gallium in spiked biological samples, using a previous extraction step in n-butyl acetate to avoid interference from Fe(III) and Cu(II).