Polarographic Behavior of Diethylenetriaminepentaacetic Acid at the Dropping Mercury Electrode

Abstract

Anodic waves of DTPA at DME in the presence and in the absence of calcium(II) and magnesium(II) ions were studied systematically, and the stability constants of mercury(II)-DTPA chelates were determined. The electrode reaction for the anodic waves of DTPA proceeds reversibly in a polarographic sense. In the presence of magnesium(II) ions, however, DTPA gives an irreversible wave. This may be ascribed to the slow reaction of the magnesium(II)-DTPA chelate. The use of DTPA as a titrant in the amperometric titration of metal ions which do not yield a polarographic wave under the usual polarographic conditions was also discussed briefly.Many works on the chelate formation reaction of diethylenetriaminepentaacetic acid (DTPA) with mercury(II) ions have been published.1-3) In an acid medium, DTPA forms 1-to-1 normal and hydrogen chelates with mercury(II) which are considerably more stable than the corresponding mercury(II)-EDTA chelates. This can be attributed to the increased number of donor atoms present and to the more basic character of DTPA.2)As in the case of EDTA,4) DTPA gives rise a single well-defined anodic wave at the dropping mercury electrode (DME). The present work was undertaken in an attempt to obtain insight concerning the electrode reaction mechanism of DTPA anodic waves in the presence and in the absence of calcium(II) and magnesium(II) ions, and to study the complexation reaction of DTPA with mercury-(II) by the polarographic method.The use of DTPA as a titrant in the amperometric determination of calcium(II) and lanthanum(III), which do not yield a reduction wave under the usual polarographic conditions, was also examined. ExperimentalAll polarographic studies were carried out in anThe ionic strength of the solution was adjusted by adding appropriate amounts of sodium perchlorate. The oxygen dissolved in the sample solution was removed by bubbling pure nitrogen gas through the solution. The d.c. current-voltage curves were measured by a manual polarograph similar to that of Kolthoff andLingane5)The a.c. and d.c. polarograms were recorded automatically by a Yanagimoto Galvarecorder GA-103. The d.c. polarographic data given in this paper were corrected for the residual current and the ohmic drop of the cell circuit.For all the measurements we used a dropping mercury electrode with an m value of 1.240 mg/sec and a drop time td of 4.80 sec at a mercury height of 60 cm in an 4.80 at -0.60 V vs. SCE.A saturated calomel electrode with a large surface area was used as the reference electrode.When the a.c. polarograms were recorded, a platinum wire electrode with a large surface area was inserted into the electrolytic solution as a third electrode. in order to minimize the impedance of the cell.6) DTPA of analytical reagent grade was recrystallized from an aqueous solution by adding an excess amount of hydrochloric acid, and dissolved into the redistilled water by neutralizing it with a suitable amount of sodium hydroxide. The concentration of the DTPA solution was checked by Mg titration, using Eriochrom ...

Amperometric titrations

“…Microgram amounts of magnesium have been titrated with EDTA at a rotating mercury electrode (75). The polarography of diethylenetriaminepentaacetic acid has been examined and applied to the amperometric titration (143) and ac titration (144) of calcium and lanthanum.…”

Organic polarography

“…Diethylenetriaminepentaacetic acid in the presence of Mg(II) and Ca(II) (685), ethylenediaminetetraacetic acid and related compounds at the carbon paste electrode (674, 675), and ethylenediaminetetraacetic acid, A7-hydroxyethylenediamine-A7,A7',AT"-triacetic acid, and diethylenetriaminepentaacetic acid (914) were studied by anodic polarography. A description was given on the effect of anionic surfactants on the reduction of Cu(II)-ethylenediaminetetraacetate complex by ac polarography (565).…”