Determination of Trace Elements by Solid-phase Spectrophotometry after Collection on a membrane filter

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1.Determination of uranium(VI)in seawaterUranium(VI) was collected on a membrane filter as a complex with 3-[4-(5-bromo-2- pyridylazo)-3-hydroxy-N-propylanilino]propanesufonate(5-Br-PAPS), together with the ion-pair precipitate formed between Zephiramine and perchlorate ions, and determined by solid-state spectrophotometry. The selectivity of the method could be improved with the use of trans-cyclohexane-1,2-diaminetetraacetic acid and an ethylenediamine buffer solution of pH 7. Except for carbonate ion, other trace elements and the major constituents of seawater did not affect the determination of uranium. The interference from the carbonate ion was eliminated by the removal of the ion as carbon dioxide from the acidified seawater sample with ultrasonic agitation. The concentration of uranium in a seawater sample was found to be 3.26 mugLAMBDA with a relative standard deviation of 2.2% (n=21) for 30-50 ml of seawater.2.Determination of cobalt(II) in white wineCobalt(II) was made to react with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(5-Br- PADAP) at pH 5 in the presence of hydrogen peroxide and a ligand buffer solution composed of ethylenediaminetetraacetic acid and an excess of zinc(II). The reaction mixture was then acidified to pH 1.8 by the addition of perchloric acid and the cobalt(III)-5- Br-PADAP was collected on a membrane filter. The complex on the filter was determined by solid-phase spectrophotometry. Inorganic trace elements and major constituents of white wine did not affect the determination of cobalt(II). The effect of alcohol could be eliminated by 1:1 dilution of wine samples with water. The concentration of cobalt in 10 different wine samples was in the range 2.4-5.6 mugLAMBDA.