Table I. Calibration Data t = 4.57 sec. m = 1.763 mg. per sec.
= 1.88 0.1M NH,SCN, 0.017M pyrogallol pH 1.0 mmtli6
Tin
__
Concn., 111
M
id
0 167 0 334 0 501 0 668
0 836 1 6i
2 13, 2 00, 2 08 4 36, 4 32, 4 04 6 30. 6 12. 6 36 8.80: 8 . 2 4 ’ 11.0; 10.8 21.6 Av. 1 2 . 7 rt 0 . 3 1
id/C 12 7 , 12 0, 12 4 13 0, 12 9, 12 1 12 6. 12 2 , 12 7 13.2: 1 2 . 3 1 3 . 1 ; 12.9 12.9
DISCUSSION
The effect of pyrogallol on the tin wave was studied in solutions of 0.1M ammonium thiocyanate-0.33mM tin (IV) a t a pH of 1.0. The current did not attain its limiting value until a 3 to 1 molar ratio of pyrogallol to tin was reached. A slight maximum in the tin(IV)/tin(II) reduction wave is easily eliminated by a trace of a maxima suppressor. Pyrogallol had no effect on the indium rrduction wave a t the concentrations uscd in this work. The cffcct of pH was studied in solu-
Concn., mM 0 238 0 476 0 714 0,952 1.19 2.38
Indium ‘Id
2 44, 2 56, 2 46, 2 52 5 00, 4 88, 4 88, 5 00 7 32, 7 32, 7 32 9.76, 9.76 12.3, 12.3 24.8 1 0 . 3 f 0.10
tions containing 0.33m.M tin(IV), 0.1h’ ammonium thiocyanate, and 0.2% (w./v.) pyrogallol. In 1.16.11 and 0.4661 perchloric acid, the tin waye is poorly formed. The best waves, from an analytical viewpoint, are obtained a t a pH of 1.0. At a pH of 2.0, the limiting current for the tin (11)/tin (0) reduction shows a slight decrease and the tin(1V) /tin(II) reduction is poorly defined with a shift in the half-wave potential to a more negative value (about -0.21 volts us. S.C.E.). This decrease in wave height and change of
id/C 10 3 , 10 7 , 10 3 , 1 0 G 10 5 , 10 2 , 10 2 , 10 5
10 2 , 10 2 , 10 2 1 0 . 3 , 10.3 10.3, 10.3 10.3
potential become more pronounced as the pI1 is increased. LITERATURE CITED
(1) Kolthoff, I.
M., Lingane, J. J., “Polarography,” 2nd ed., p. 519, Interscience, New York, 1952.
(2) Ibicl., pp. 523-6. (3) 67, ~, Linnane. J. J.. J . A m . Chem. SOC. 919 (i945j. ’ (4) Phillips, S. I,., ANAL.CHEM.32, 1062 (1960). (5) Phillips, S. L., Morgan, E., Zbid., 31, 1467(1959). RECEIVED for review September 14, 1960. Accepted May 29, 1961.
Cathodic Action of the Uranyl-EDTA Complex at the Drop ping M e rc ury Electrode TSAI-TEH LA1 and TEH-LIANG CHANG Analytical Chemisfry Laboratory, Cheng Kung Universify, Tainan, Taiwan
b The polarographic behavior of the uranyl (ethylenedinitri1o)tetraacetate complex has been studied over the pH range 3.3 to 9.3. A reversible wave corresponding to the reduction of the uranyl complex to the U(V) state was obtained in this pH range. The half-wave potential was found to be independent of pH from 5.7 to 6.8 and equal to -0.37 volt v5. S.C.E.; outside this range the halfwave potential is pH-dependent, and this has shown that one hydrogen or hydroxyl ion is involved in the reduction. It was proved that UIVI) has one more ligand attached than U(V) in the pH range from 3.3 to 6.8, but has the same number of ligands between 6.8 and 9.3. The diffusion current is proportional to concentration of uranyl ion from 2.20 X 10-4M to 2.4 X 1 O-3M. The diffusion current constant is 2.1 8 for 7.13 X 1 O-2M Versene at pH 5.50 and the diffusion coefficient is 1.30 X 1 0-5 sq. cm. per second.
-
T
chelate formation between (ethylenedinitri1o)tetraacetic acid (EDTA) and a number of metal ions wasstudied most extensively by Schwarzenbach and coworkers. As supporting electrolyte or masking agent, EDTA was used in the polarographic determination of metals. Ishibashi and Fujinaga (5) have used double complesing agents of EDTA-Na4P107 as a base solution for some inorganic ions, especially uranyl ion. Some papers have discussed the polarographic behavior of metal chelate compounds using EDTA as chelating agent. Pecsok and Juvet (12) have studied the vanadium-EDTA complex over the pH range 5 to 12.6, and Kolthoff and Auerbach (6) have studied the iron-EDTA complex in the pH range of 1.0 to 10.9. The polarographic behavior of the copper and europium complex with EDTA has been reported by Pecsok ( 1 1 ) and Onstoff ( I O ) , respectively. HE
The uranyl-EDTA complex has been studied by p H titration (I), ultraviolet spectroscopy ( I S ) , and high-frequency titration (3, 14). At nearly the same period as our present work, Davis (2) studied the polarography of the uranium (VI)-EDTA complex. EXPERIMENTAL
Polarographic measurements were made using a Fisher Elecdropode and all potentials were measured with an external potentiometer. The modified H-cell with external saturated calomel electrode was placed in a thermostat maintained a t 30’ rt 0.1’ C. and hydrogen gas was used to remove oxygen from solutions. The capillary had a rate of flow of 1.105 mg. per second and a drop time of 4.94 seconds per drop a t an applied potential of -0.500 volt vs. S.C.E. in 1M sodium perchlorate solution. The pH of the solution was adjusted by additions of perchloric acid or sodium VOL. 33, NO. 9, AUGUST 1961
1193
t
3
I
l
-
-.a
-.l
v
q,q
-.4
-.3
-.5
-,6
S.C.E.
Figure 1.
Figure 2.
Typical polarograms
hydroxide and determined by a Beckman Model H-2 pH meter. Stock solutions of uranyl perchlorate were prepared from uranyl acetate by double fuming with perchloric acid, and were standardized volumetrically with potassium dichromate after reduction with zinc amalgam and aeration. Oxidimetric standard potassium dichromate
Co., Inc.), and were standardized with metallic zinc (16). Gelatin (0.005%) was used as a maximum suppressor. All the chemicals used were of reagent grade.
Of
Harris and Kolthoff (4), in polarographic studies of acid solutions of uranium, obtained a reversible first wave with a half-wave potential of
Bureau
RESULTS AND DISCUSSION
Table I. Relation among i d r € 1 1 2 ~ €air and pH (All polarographic solutions contain 1.10 X lO-3M uranyl erchlorate, 0.2M sodium perchlorate, 9.03 X 10-ZM Versene, and 0.005& gelatin.) pH i, pa. Em Ea14 - Ell4 PH 6 pa. E112 E314 - & 4 -0.061 -0.357 -0.252 5.95 3.05 4.00 -0.064 3.30 -0.066 -0.373 2.96 6.00 -0.066 3.44 -0.255 3.98 -0.063 -0.376 2.95 6.15 -0.063 -0.268 3.75 3.60 -0.061 -0.375 2.97 6.25 -0.260 -0.067 3.75 3.62 -0.060 -0.372 2.84 6.30 -0.283 -0.065 3.73 3.76 -0.056 -0.370 6.45 2.78 -0.295 -0.058 3.46 4.00 -0.061 -0.375 2.82 -0.274 6.50 -0.063 3.40 4.20 -0.055 -0.377 2.62 6.71 -0.298 -0.057 4.40 3.24 -0.059 -0.391 2.50 -0.063 7.00 4.50 -0.285 3.40 -0.059 -0.402 2.37 7.10 -0.060 4.70 -0.316 3.23 -0.061 -0.426 2.40 -0.055 -0.303 7.60 4.82 3.36 -0.061 -0.431 2.20 -0.057 -0.320 7.85 5.05 3.27 -0.064 -0.429 2.06 -0.060 7.88 3.12 -0.330 5.18 -0.431 -0.058 2.20 7.89 -0.054 2.88 5.30 -0.326 -0.059 -0.471 2.04 -0.060 8.25 3.12 -0.327 5.39 -0.479 -0.056 2.22 8.49 -0.330 5.40 3.11 -0.058 -0.063 -0.493 2.13 -0.059 -0.331 8.78 3.13 5.42 -0.501 -0.063 2.01 -0.063 8.89 -0.348 3.28 5.50 -0.062 -0.539 1.94 9.30 -0.056 -0.365 5.70 3.16 -0.522 -0.063 1.74 9.30 -0.365 3.07 -0.061 5.80 Table II.
h, Cm.
4
82.9 76.6 69.3 61.1 53.0
9.11 8.75 8.33 7.82 7.28 6.64
44.1
1194
*
Effect
of Mercury Pressure
Dropping
Rate of
Sec./Drop 3.99 4.33 4.87 5.41 6.27 7.70
Mg./Sec. 1.269 1.168 1.042 0.939 0.780 0.671
ANALYTICAL CHEMISTRY
Time,
- i ) vs. E
1.10 X 10-*M UOs (ClO,)*, 9.03 X 10-*M Verrenc, 0.2M NaCl01 0.005qb gelatin
.
1 10 X 10-*M U Q (ClOJb 0.2M NaClOb and 0.005% gelatin I. AtpH3.30 11. Plus 9.03 X lO-%i Verrene at pH 4.40 111. Plus 9.03 X 1 O-?M Venene at pH 5.50
Standards, 136AJ was used. Stock solutions of versene were prepared from the disodium salt of (ethylenedinitril0)tetraacetic acid (Matheson
Plots of log i / ( h
Flow,
i d , pa.
3.95 3.79 3.58 3.40 3.15 2.88
i d /
