Spectrophotometric Determination of Tech netium(Vl1) with Thioglycolic Acid F. J. MILLER and P. F. THOMASON Analytical Chemistry Division, Oak Ridge Nafional laboratory, Oak Ridge, Tenn.
b A spectrophotometric method of analysis for technetium(Vl1) has been developed to supplement the radiochemical and polarographic methods that are now used in laboratories of radiochemical processing plants. Technetium is determined as the pertechnetote ion in the concentration range from 2 to 40 pg. per ml. in the final solution by measuring at 655 mp the intensity of the color that is formed at pH 8.0 with thioglycolic acid. Beer’s law is obeyed over this range. The molar absorptivity is estimated to be of the order of 1800. Few anions interfere. The time required for the determination is short, and the technique is simple.
T
PRODUCTION of appreciable quantities of technetium in radiochemical processing plants has aroused interest in the development of a spectrophotometric method of analysis that could be used to supplement the radiochemical and polarographic methods that are now in use. Some colorimetric reagents were already known. In his excellent review article ( I ) , Boyd has described the use of the thiocyanate complex to estimate technetium(V) and the use of the 247- and 289-mp absorption bands to estimate technetium(VI1). In a preliminary communication by Jasim, Magee, and Wilson ( d ) , reagents are listed which are stated to produce colors with technetium in its different oxidation states. Experimental procedures for the development of the colors are also given. Thioglycolic acid has been known as a colorimetric reagent since 1927 (3). It has been used as a chromogen in the determination of iron, tungstate, uranyl, and other ions.
tralized to p H 8.0 i0.2 with ammonium hydroxide before it was made up to final volume with water. Sodium Acetate Solution. A 1M aqueous solution of sodium acetate was prepared from reagent grade sodium acetate t o be used as a buffer solution. Spectrophotometers. Three different spectrophotometers were used in the development of the method: a Cary Model 14P recording spectrophotometer, a Warren Spectracord, and a Beckman Model B spectrophotometer.
HE
REAGENTS AND APPARATUS
Standard Solution of Potassium Pertechnetate. This solution, which contained 0.423 mg. of potassium pertechnetate per ml., was obtained from Q. V. Larson of the ORYL Chemistry Division. Thioglycolic Acid Solution. This was a 10% v./v. solution prepared from purified thioglycolic acid that was obtained from Fisher Scientific Co. The thioglycolic acid solution was neu-
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Figure 1 . Absorption spectrum of technetium thioglycolate from 360 to
700 mp The recording spectrophotometers were very useful in the preliminary investigation of the spectra. The width of the 655-mp absorption peak of the technetium-thioglycolate permits the use of less elaborate instruments for routine work. EXPERIMENTAL PROCEDURES
The calibration curves were prepared as follows: From the standard solution of potassium pertechnetate, suitable aliquots that contained from 10 to 200 pg. of technetium(VI1) were taken. These aliquots were transferred to 5-ml. volumetric flasks. To each aliquot was added 1 ml. of 1M sodium acetate solution and then 1 ml. of 10% v./v. thioglycolic acid solution of pH 8.0 =k 0.2. The flasks were placed on a boiling water bath and were heated for 15 minutes. The solutions were cooled and diluted to 5-ml. volume with water. The pH of each solution was checked to ensure that it did not vary from 8.0
i 0.2, the desired value. The absorbance of each solution was measured on the Beckman Model B spectrophotometer a t a wave length of 655 mp in a cell of 1-cm. path length. The reference solution was a blank of reagents. A calibration curve was then prepared by plotting absorbance us. concentration of technetium(VI1). Test solutions were treated in the same manner, and their technetium contents were determined from the calibration curve. DISCUSSION
The reaction of thioglycolic acid with technetium(VI1) in basic medium produces a green color of maximum absorbance at 655 mp. The intensity of the color is proportional to the technetium (VII) Concentration. A study of the color development as a function of time has shown that the reaction requires approximately 1 hour a t room temperature to reach stability. After an hour, the color is stable for a t least 24 hours. The time required for the color to become stable can be shortened by heating the solution on a boiling water bath for 15 minutes. The proportionality between the intensity of color in the solution and the technetium(VI1) concentration was tested by varying the technetium(VI1) concentration of a number of solutions and measuring the absorbance of the solutions after the color had developed completely. The absorbance of the solutions obeys Beer’s law over the range of technetium concentration from 2 to 40 pg. per ml. in the solution on which the absorbance measurement is made. The molar absorptivity is estimated to be of the order of 1800. It is recommended, however, in determining the technetium(VI1) content of test solutions that a calibration curve be made, as is usually the procedure in analytical methods. Both the absorption spectrum and the intensity of the color vary with pH. At a p H of 5 and lower, a reddish brown color is produced that has general absorption from 350 to 500 mp. At higher pH values, a broad peak of maximum a t 655 mp is obtained. The absorbance of the peak a t 655 mp decreases slightly a t a p H higher than 8.0 f 0.2. Accordingly, it is recom\101. 32, NO. 1 1 , OCTOBER 1960
1429
Table 1. Calibration Curve Data Wave length, 655 m r Slit width, 0.130 mm. Cell, 1-cm. Composition of final solution: Indicated volume of standard solution of KTcO, (0.207 mg. of.Tc(VII)/ml.); 1.0 ml. of 10% v./v. thioglycolic acid solution of pH 8.0 f 0.2; 1.0 ml. of 1 M sodium acetate solution; and water, to make a total volume of 5.0 ml. pH of final solution, 8.0 f 0.2 Reference solution, reagent blank
TcWII) ‘Vol. of Std. S o h , Content, M1. Mg. 0.050 0.100
0.250 0.500 0.750 1.000 a
0.01C 0.021 0.052 0.104 0.155 0.207
i4bsOrbance” Beckman Cary Model B 0.042 0.080
0.i93
0.045 0.083 .. _ _ _ 0.192 0.370 0.542 0.721
0.362 0.543 0.720 Absorbance values on the Gary and
the Beckman Model B instruments were taken on different days and on different test solutions.
mended that standard and test solutions be adjusted to p H 8.0 f 0.2. The spectrum of the standard solution, measured against a reagent blank, after full development of the color is shown in Figure 1. The reagent blank itself is colorless; it shows no absorption at 655 mp when read against distilled water as the reference liquid.
The effect of the following anions on the color development was studied separately by adding an aliquot of a standard solution of each of the anions in order t o obtain a 10 to 1 weight ratio of the anion to the technetium in the final solution: chloride, fluoride, bromide, iodide, phosphate, sulfate, tungstate, molybdate, dichromate, ruthenate, and rhenate. Significant interference was obtained only in the case of the molybdate, dichromate, and ruthenate ions. Adequate methods of separating technetium from these interfering anions are already available in the literature (I), It was not considered necessary to study the effect of cations on the determination since the separation of technetium as the pertechnetate ion from any color-producing cation can be accomplished readily by hydrolytic mcans, by ion-exchange chromatography, or by extraction. Data are given in Table I that were used to construct the calibration curve. I n Table 11, the results for two test solutions are given. The similarity of the data obtained on the Gary recording spectrophotometer and on the Beckman Model B spectrophotometer demonstrates the feasibility of the use of the simpler instrument in this procedure. The method described is especially suitable for control laboratory use. The time required for an analysis is
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Table II. Absorbance Data for Test Solutions Conditions same as for Table I except that a test solution of the volume indicated
was used instead of standard solution of KTcO~ Vol. of TclVII) Content of Test Soln., AbsorbTest Solution Ml. ance Mg. Mg./ml. Test Solution A 0 050
0 032
0 009
0.180
0.500 1.000
0.i72 0.333 0.653
0.093 0.183
0.186 0.183
0.250
0.047 0.iSS
Test Solution B 0.500 0.500
0.300 0.299
0.084 0.084
0.167 0.167
0 250
Test Solution C 0.212 0.059 0 418 0 117 0 810 0 225
0.236 0 234 0 225
0 500 1 000
short, the technique is simple, and the apparatus is generally available. LITERATURE CITED
(1) Boyd, G. E., J. Chem. Educ. 3 6 , 3 f 1959). (2) Jasim, F., Magee, R. J., Wilson, C. L., TaEanta 2,93 (1959). (3) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 2nd ed., p. 378, Interscience, New York, 1950.
RECEIVEDfor review .March 2, 1960. Accepted June 2, 1960.
Fluorometric Determination of Uranium in Zirconium and Hafnium P. A. VOZZELLA,’ A. S. POWELL, R. H. GALE, and J. E. KELLY2 Materials Development laboratory, Nuclear Division, Combustion Engineering, Inc., Windsor, Conn.
b The extraction of microgram quantities of uranium with ethyl acetate has been found suitable for the determination of trace amounts of uranium in zirconium. Half-gram samples are dissolved in nitric and hydrofluoric acids, the hydrofluoric acid i s removed, and the solution is made up to a definite volume. An aliquot is pipetted into a vial containing a salting agent and the uranium extracted with ethyl acetate. The amount of uranium in the organic layer is determined fluorometrically. Any quenching occurring is compensated for by the use of control standards. The concentration of uranium in hydrofluoric-nitric acid pickling baths is determined by the standard addition of uranium to a duplicate of 1430
ANALYTICAL CHEMISTRY
the sample being analyzed. Study of the variables in fluorometric determination of uranium has indicated those which must b e controlled to get best precision and accuracy.
F
development of a fuel element failure detection system for a pressurized-water nuclear reactor, it was necessary to determine the amount of uranium present in Zircaloy as a n impurity. This concentration, about 1 p.p.m., could not be determined by ordinary chemical means. A fluorometric procedure which is rapid, selective, and sensitive has been adopted for the analysis of routine samples by this laboratory. OR THE DESIGN and
The most recent article found in the literature on the fluorometric determination of uranium was that presented by Centanni, Ross, and DeSesa (2). After extensive investigation, this method was adapted to the determination of uranium and zirconium. Modifications both in the instrument aild procedure since the presentation of these papers have been published by Centanni and Morrison ( 1 ) . The procedure recommended is also suitable for the determination of uranium in hafnium. 1 Present address, Connecticut Aircraft h’uclear Engineering Laboratory, Middletown, C o n i 2 Present address, New Departure Co., Bristol, Conn.
