Determination of Vanadium with Square Wave Polarograph

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It has been a usual method in the polarographic determination of vanadium to utilize the anodic wave produced by the oxidation of vanadyl ion (IV) to vanadate ion (V) in a supproting electrolyte composed of 1 M sodium hydroxide and 0.08 M sodium sulphite.1) Recently, Musha and Takao studied on the simultaneous determination of titanium and vanadium using a base solution of 0.1 M EDTA and 0.02 M sodium citrate.2) However, these supporting electrolytes can not be applied to the high sensitive determination with square wave polaroglaph, since the reactions of vanadium ions in these supporting solutions appear to proceed irreversibly, or to be accompanied by a chemical reaction. Only an available reversible reaction for this purpose in the consecutive reduction processes of vanadium ions is a reaction between vanadic (III) and vanadous (II). As the half wave potential of this reaction in 1 N sulphuric acid is -0.508±0.002 V. res. S.C.E. and that of the reaction between vanadyl (IV) and vanadous (II) in 0.1 N sulphuric acid is -0.85 V. res. S.C.E., it is impossible to reduce vanadyl (IV) ion direct-ly to vanadic (III) ion. Thus, for the high sensitive determination of total vanadium with square wave polarograph it is necessary to convert aII vanadium ions into the state of either vanadic (III) or vanadous (II). It is accepted in general that when a oxidation-reduction reaction invoIVes a process of formation or breaking of covalent metal-oxygen bond, the reversibility of the redox reaction becomes very poor. The irreversibility of the reaction between vanadyl (IV) and vanadous (II) may be caused from the formation of a metal-oxygen bond VO++ which is invoIVed in the reaction process between vanadyl (IV) and vanadic (III). Therefore, it is expected that the reversibility of the reaction between vanadyl ion (IV) and vanadous ion (II) may be increased by preventing the formation of VO++ ion, using a much higher concentrated sulphuric acid as a supportinng electrolyte, in which VO++ ion is scarcely formed. The aim of the present study was to obtain informations for the determination of vanadium with square wave polarograph, utilising the reaction between vanadyl (IV) and vanadous (II) in a highly concentrated sulphuric acid on the basis of the abovementioned expectation.
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Determination of Vanadium with Square Wave Polarograph

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