1714
A N A L Y T I C A L CHEMISTRY D l S C b SSIOh-
Table J.
Determination of Niobium Beta.___ Counts/XIin./Ml. ~1 2
Regular method, no Hd'Oh added 1 . 2 1 X 10' 1 2.5 X 10' 1.42 X lOdQ 1 . 8 0 X IO@ Regular method, 100 mg. HaPo4 added New method, 100 mg. IIaPOi added 1 . 2 0 X 10' 1 17 X 104 a Final NbnOr precipitate neighed more than added carrier.
Step 1. Place thtl sample ( 2 nil. or lcss in volume) in a 50-nil. glass centrifuge tube, and add 2 nil. of saturated oxalic acid solution and 2 ml. of niobium carrier (20 to 30 nig. of niobium pentoside). Stir and add 1 ml. of 6 .If hydrochloric acid; then add 7 ml. of 55.6% iodic acid solution (100 grams of iodic acid dissolved in 80 nil. of hot water). Stir thoroughly, add 10 ml. of concentrated nitric acid, and stir again. Usually a precipitate f o r m immediately upon the addition of the nitric acid. Digest in a hot water bath (90" to 100' C.) with occasional stirring for 15 to 20 minutes. (-4 brown color sometimes fornis due to the reduction of the iodate to free iodine by the oxalic acid.) After digesting, centrifuge and discard the supernatant I Initric acid, solution. Stir up the precipitate with 3 ml. of 6 , 2 nil. of 6 31 ammonium hydroxide, and 5 ml. of water. Heat the mixture nearly to boiling, transfer to a 50-ml. Luet.eroid tube, centrifuge, and discard the supernate. Step 2 . Follow Glendenin's procedure (3) from this point on, starting with Step 2: "Dipsolvp the Sb206 in 1 ml. of 27 34 HF , . . , . . "
Tho mc,tliod gave sati5factoi.y decontamination from barium, cerium, ruthenium, strontium, and zirconium activities; it was tested using pure niobium tracer and by analyzing several solution? containing mixed fission product,s and uranium. Results given in Table I represent duplicate analyses from a typical solution of the follolving composition (rouiit* per minute): 8 0 x 104 Total rare e a r t i r i H 1 4 X 108 8 o x 104 I 1 x 106 4hout 10 mg./ml.
ZrB
LITERATURE CITED (1) Corvrll, C. D., and Bugarman, X.,
"Radiochernical Studies.
The Fission Products, Book 3." paper 253 by L. E. Glendenin, p. 1523, National Nuclear Energy Series, Div. I\', Vol. 9, S e w Tork, AIcGraw-Hill Book Co., 1951. ( 2 ) Ibid., p. 1524. (3) Ihid.. p. 1525. ( 4 ) Hahn, K.B., J . A m . Cheni. Soc., in press. RECEIVED May 5 , 1951. Work perfornied under Contract W-7405eng 26 for t h e Atomic Energy Project a t Oak Ridge National Laboratory.
Method of Standardization for Polarographic Determination of Lead in Zinc and Zinc-Bearing Materials PHOEBE RUTHERFORD
AND
L. 4 . CHA
Zinc Smelting Division, S t . Joseph Lead Co. of Pennsylvania, .klorlucu, Pu.
v
ARIATIOKS in the values of polarographic diffusion currents as a function of solvent or solution viscosity have been reported by a number of authors. Peracchio and Meloche ( 6 ) , for example, measured the diffusion currents of sodium and potassium chlorides in ethylene glycol, trimethylene glycol, and glycerol. I n these solvents of relatively high viscosity, the diffusion currents for both alkali halides were considerably lower than those observed in aqueous solution. Similarly, Brasher and Jones (1) studied certain inorganic ions in aqueous solutions of various concentrations of sulfuric acicl. .sodium hydroxide, and sodium sulfate. Their reasoning involved the Ilkovi6 equation, i d = 605 nD~'*Cm*/StllE, where id is the diffusion current, n i s the number of faradays of electricity per mole of the electrode reaction, D is the diffusion coefficient, C is the concentration in inillimoles per liter, m is the rate of flow of mercury in milligrams per second, and t is the drop time in seconds. Only changes in D , m, or 1 would affect the diffusion current for any given C. Changes in m were negligible in the range of concentrations studied. Thev corrected t to a constant value in each case because it vaned. This left only D as a variable. Then, because idaD112 (Ilkovif equation), and Daq (Stokes-Einstein equation), where 7 is viscosity, i d 6 Their experimental evidence as prepented bore out this relationship. The viscosities were measured by an Ostwald-type viscometer a t 25 O relative t o water. Viscosities a t intermediate concentrations were taken from a plot of log 77 against concentration. Brasher and Jones concluded that change in the diffusion current for a given concentration of a reducible substance was a function of viscosity only. Collenberg and Scholander ( 2 ) reported a linear relationship between Z/rland eoncentration of the electrolyte. They presentetl the following equation relating the diffusion current of metal ion.: to the concentration c, of the electrolyte: id = k ( - u c f b ) , also q - l I a = --ac b, where a and b are constants characteristic of the electrolyte. They reported that the constantq npre the
+
same for a given electrolyte whethcr measured by puiarograph or viscometer. They worked with zinc chloride as one of the electrolytes, but presented data only in very general form. McKenzie (6) reported that the diffusioncurrent for metal ions was proportional to I/< He and Gentry (3) reported that the product of the diffusion current and d G i s a constant. Deviations that may arise from a similar cause have been noted in this laboratory. The zinc-bearing materials that are analyzed vary widely in both lead and zinc contents. Variations in the diffusion current of lead ion a$ a function of zinc ion concentration are conimonly observed. Bccordingly, this effect was studied in order to determine the exact relationship. As a result of this study, a method for rapid diffu-ion current corrections in routine analysic: has been developed. 4 n y change in capillary characteristics may be quickly detected and compensated. APPARATUS AND PROCEDURE
A Fisher Electropode and a Sargent Model XXI olarograph were the instruments used. Three different capigaries were employed a t various t h e e : one n-ith the Fisher, and two with the Sargent instruments. Titer test tubes, 4 inches in height and 1 inch in diameter, held the solutions to be analyzed, The tubes with their solutions were clamped in a rotating rack immersed in a water bath. Each tube contained several milliliters of mercury a t the bottom to serve as eventual anode. The dropping mercury electrode and the anode connection to the mercury pool extended through a rubber stopper, so that the whole electrode assembly could be transferred rapidly to succeeding cells. Piitrogen was used for degassing the solutions. All samples in this investigation were synthetic nlixtures prepared from zinc and lead metal of high purity. To each preparation was added concentrated hydrochloric acid, about 3 ml. in excess of that required for complete solution of the metals. Ten nlilliliters of aqueous 0.05yo sodium carboxymethylcellulose were used as a maximum suppressor i n each case. Finally, each sample was diluted to 50 nil. in a volumetric flask, and the resulting Polution n . a ~analyzed polarogirlphically in the u ~ u a manner. l
V O L U M E 23, N O . 11, N O V E M B E R 1 9 5 1 The viscosities of these solutions were determined with an Ostwald-type viscometer a t 24" C. Several intermediate values were deternuned in addition to the concentrations used for the lead determinations. R E S U L r S A N D D1SC:USSIOS
Three series of determinations were made, one for each capillary. Within each series polarograms were made not only for solutions for which the zinc ion concentration was varied, but al.so for solutions in which lead ion concentration was varied as the zinc ion concentration was held constant. Diffusion currents were recorded directly in microamperes n-ith the Sargent polarograph and in arbitrary galvanometer division units wit,h the Fisher instrument. T h e n a given set of dat,a was plot,ted 011 seniilogarithmic graph paper with diffusion current per milligram of lead t ~ ordimtes 9 and grams of zinc per 50 ml. of solution as abscissas, all points tended to lie on a straight line. Furthermore, all lines for the three sets of data were parallel to each ot,her but not to the a b s c i s a The data from which the lines m-ere plotted are shown in Table I.
Table I Z!nc, i; .,0 .\I1
SIg. '50 311.
id
(Obsd.)
io
0.84 0.84 0 836
0.850 0 846
0 5
5.0 10.0 15.0 20.0
0 840
2 . F,
6.25 18.75 40.0
0.84 0.84 0.84 0.825 0.80 0 79 0.80 0 62 0 63 0 62 0.63
10 0
0.I
2.5
10.0
Supposing that a new capillary is being placed in service or that certain characteristics of an old capillary in m e have become changed. A single sample of known zinc and lead contents is analyzed polarographically; and, from the observed diffueion current, one point on the graph can be fixed. By extending through this point a line of the same slope as t h a t noted above, the corrected diffusion current for a given zinc ion concentration may be found. In actual use in t'his laboratory, a sheet of semilogarithmic paper is mounted on a baseboard and covered with a shei~tof Plexiglas. A cursor bearing a hairline of the proper slope noted above is moved to coincide with the fixed point rst;iblished with the sample of known concentration. With the cursor in this position, values of the diffusion current of lead for othrr zinc ion concentrations can he ready easil Th? gvaphical relntionPhip may he esplaineJby the follon-ing c.c~uatlnn:
.
5.0 7.5 10.0 15.0 Sargent X S I , Capillary 2 1.0 0,612 5.0 0.617 10.0 0.616 20.0 0.613 0,575 1.0 5.0 0,577 10.0 0,580 20.0 0.569 1.0 0,464 5.0 0,458 10.0 0.434 20.0 0.439 Fisher Elecdropode 0.5 28.8 1.0 27.9 5.0 28.4 10 0 29.5 20.0 29.3 50.0 29.1 1 0 26.8 5.0 26 3 10.0 26.8 20 0 27 5 27 1 50 0 1 0 22 3 5 0 21 7 10 0 21.2 '0 0 21 1
here .z is the number of grams of zinc inn in 50 nil. of solution,
