D. J. Fisher

DETERMINATION OF TRACE QUANTITIES OF URANIUM BY CONTROLLED-POTENTIAL DC POLAROGRAPHY IN A TRI-n-OCTYLPHOSPHINE OXIDE EXTRACT

Abstract The combination of solvent extraction and controlled-potential dc polarography directly in the organic extract provides a sensitive and selective method for the determination of uranium. The method should be applicable to a wide range of samples containing trace concentrations of uranium, such as sea water, and waste streams. Uranium concentrations as low as 2.4 μg in 250 ml of sample can be determined when a 5-ml polarographic cell is used. If a smaller polarographic cell is used, as is shown in another paper in this symposium (8), an evaporation step can be added after the extraction and as little as 0.2 μg of uranium determined in 250 ml of sample. The method compares favorably in precision with colorimetric methods for uranium and is more selective and free from interferences.

Controlled-potential polarography and coulometry as microanalytical techniques☆☆☆

Abstract The three electrode, controlled-potential technique in polarography allows the use of very small reference electrodes, such as small calomel or silver-silver chloride electrodes or a quasi-reference electrode, which either have too high a resistance or are too easily polarized to permit their use with a conventional polarograph. This technique also permits the use of solutions of relatively high specific resistance in the polarographic cell, thus permitting one to use organic media or dilute supporting electrolyte, which reduces the problems of blanks from this source. The capability of using small electrodes facilitates the design of micro polarographic cells. An example of application to polarography on the micro scale is described. As normally practiced at this Laboratory, controlled-potential coulometry uses quite small samples (~0.04 meq) to obtain results of high precision (0.1%). By reducing the size of the cell and the working volume, and by careful attention to details such as purity of reagents and the exclusion of oxygen from the system, it is possible to make the sample size very much smaller. By the application of suitable blank correction techniques, it is possible to determine reducible and oxidizable constituents at a level of 0.02 μeq with a precision of 1%. The applicability of controlled-potential coulometry is illustrated by the results obtained in the determination of iron, uranium, and plutonium in the range from 0.02 to 7 μeq.

Controlled-potential differential DC polarography

SummaryThis is the first in a series of papers dealing with controlled-potential differential direct-current polarography. The design of a controlled-potential differential polarograph that utilizes nonsynchronized dropping-mercury electrodes is given. The instrument incorporates circuitry to remove “drop oscillations” from conventional or differential polarograms. A gain adjustment is included in one channel so that effective equalization of the capillary characteristics of the dual electrodes can be accomplished electronically. The validity of this gain adjustment technique is evaluated. The performance of the instrument when utilized with each of the several techniques comprising differential polarography-the ΔE-differential, subtractive, and comparative polarographic techniques-is illustrated.ZusammenfassungDie Differential-Gleichstrompolarographie mit Potentialkontrolle wird diskutiert und ein entsprechendes Gerät wird beschrieben, bei dem nicht-synchronisierte Quecksilbertropfelektroden benutzt werden. Bei diesem Instrument werden „Tropfen-Oscillationen“ aus konventionellen oder Differentialpolarogrammen entfernt, und die Capillarcharakteristiken der Doppelelektrode werden elektrisch angeglichen. Der Einsatz des Geräts bei den verschiedenen differentialpolarographischen Verfahren (Δ E-Differential-, subtraktive und komparative Methode) wird erläutert.

Electronic Controlled-Potential Coulometric Titrator For Plutonium Analysis

Summary An instrument that performs coulometric redox titrations at a controlled-potential is described. A stabilized printed-circuit operational difference amplifier combined with a transistor current amplifier is used to control the potential of the electrode at which the desired reaction occurs. A portion of the electrolysis current is integrated by a stabilized printed-circuit operational amplifier connected as a time integrator, and the integral is read out as a voltage. The instrument is operated completely from an a.c. line and can be operated with either manual or automatic cut-off. The calibration is absolute; results are computed from Faradays law. Accurate coulometric titration of small amounts of substances with high equivalent weights such as plutonium is possible because of the high stability of the integrator.