ELECTROCHEMICAL AND SPECTROSCOPIC STUDIES OF PERTECHNETATE AND TECHNETIUM COMPOUNDS
Abstract
The fundamental electrochemistry of pertechnetate in acidic aqueous media was studied using cyclic voltammetry, thin-layer coulometry and secondary ion mass spectrometry. A three electron reduction was determined in perchlorate and acetate media; however, a two electron reduction was observed in a formate buffer. Working electrodes were fashioned out of graphite foil and an electrodeposition performed in each of the aqueous media studied. A similar (pH dependent) pattern was observed in the negative ion SIMS spectra from the acetate and perchlorate media. However, a distinctly different negative ion SIMS spectrum was observed in the case of the formate media. A complexing mechanism was postulated for the reduction of pertechnetate in formate buffer based on the coulometric and mass spectrometric results. This was further supported by the appearance of a red-violet species at extended electrolysis times. Using size-exclusion chromatography, fast atom bombardment mass spectrometry, electrophoresis and UV-Visible spectroscopy, the red-violet species was identified as TcO(,2)(O(,2)CH)(,2) ('-). Spectroelectrochemical and ligand-exchange studies were performed on the formate system. Using a specially designed spectroelectrochemical cell, the reduction of pertechnetate in formate media and subsequent complex formation were observed. Ligand-exchange experiments were performed on the isolated complex using a series of diphosphonate ligands (methylene- diphosphonate (MDP), hydroxymethylenediphosphonate (HMDP) and 1-hydroxyethylidenediphosphonate (HEDP)). The effect of steric hindrance was observed, with MDP exhibiting the highest rate of exchange. The feasibility of utilizing liquid scintillation counting as a detection method for liquid chromatographic analysis of technetium was evaluated. The chemical quenching of constituents commonly found in liquid chromatographic mobile phases was investigated and quench corrections presented. Quantitation of technetium was achieved over a concentration range of 10('-3)M to 10('-8)M on quiescent KTcO(,4) solutions. The fast atom bombardment mass spectrometry of pertechnetate was performed. Several series of complexes of the general formula; Tc(,n)O(,n+1)('-), ..., Tc(,n)O(,n+4)('-) (n = 1 to 5) were observed, with the species Tc(,n)O(,n+3)('-) being the most abundant. The formation of these complex anionic species in the gas phase suggests that care must be taken in the interpretation of mass spectra of unknown technetium compounds.
Degree
Ph.D.
Subject Area
Analytical chemistry
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