MSTKACTThe preconcentration voltammetric behavior o f technetium at a carbon paste electrode modified with thenoyltrinuoroacet(~iie (TTA) has been investigated. It is demonstrated that enrichment of technetium on the electrode surface by complex formation with TTA is possible. Deposition of Tc(1V) takes place due t o a purely chemical reaction resulting probably Tc(TTA)+ Enhanced accumulation occurs if ; I reductive electrode potential of -0.4 V is applied, which presumal>ly causes fixation in the form of TC(TTA)~. In the subsequent voltammetric scan a characteristic peak at about -40 and +40 mV, respectively, is obtained. Tc(VI1) is not deposited, unless a reduction potential of at least -0.6 V is applied, with the pH o f the solution optimally chosen at 3.5. Therefore, it is possible t o discriminate between Tc(1V) and Tc(VI1). INTRODUCTIONTTA 1-(2-tlienoyl)-3,3,3-trifuoroacetote~ is known t o be well suited for solvent extraction of tri-and tetravalent metal ions with which complexes are fomied even in highly acidic solutions. TTA complexes have been reported also for technetium [ 1, 21, and in addition, TTA is a possible extracting agent for this radioelement in the tetravalent state [ 3 ] . These facts suggested that we try accumulation and stripping voltammetric determination o f Tc traces at an electrode chemically modified with TTA [ 4 ] .The carbon paste electrode (CPE) was chosen as the electrode most appropriate for modification with TTA [ 51. Theoretically, deposition of Tc(IV) on this electrode should proceed by a purely chemical reaction, resulting probably Tc('ITA)4. For accumulation as Tc(III), it would be necessary t o apply a reductive electrode potential in order to avoid admixtures of reducing chemicals. Tc(VI1) can also be measured provided that a sufficiently negative electrode potential is applied, generating a technetium species capable of complex formation; hence discrimination between Tc(VI1) and Tc( IV) is possible. EXPERIMENTAL;The poldrogrdph used was the Polarecord 506 in combination with the voltammetric measuring station 663 and die voltammetric controller Eb08. This equipment, as I To whom correspondence should be addressed 0 1989 VCH I'ublishcrs, Inc.well as the CPE, were supplied by Metrohni. The reference electrode was the Ag/AgCI ( 3 M KCI) electrode. A glassy carbon rod served as the auxiliary electrode. Dissolved oxygen was removed by a stream o f very pure nitrogen gas. A rotating rod was immersed in the ineasureinent solution, providing convective transport during the enrichment period. The carbon paste consisted of a homogeneous mixture of 600 mg of spectroscopically pure graphite powder, 200 RESULTSIn order to accumulate Tc(1V) at the TTA-CI'E by a purcly chemical reaction, only immersion o f the electrodc into the measurement solution for an appropriate time was necessary. Making use o f the reducibility o f Tc( JV) t o Tc(III), a voltammetric cathodic scan lollowing enrichment can be used for the quantitation. The differential pulse (DP) voltammograms thus obtain...
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