ANALYTICAL CHEMISTR,
942
or 0.001 microgram of iodine if 5 ml. are used. If desired, half quantities of solution and reagents may be used without modification of the apparatus. This sensitivity corresponds to a difference of 1’in slope between the tests and the blanks. In the averagerange of 0.05 to 0.10 microgram, the reproducibility of replicate determinations is of the order of 1O in slope or *0.001 microgram in 5 ml. of test solution. This apparatus has been extensively used for the final determination of protein-bound iodine in serum by two different procedures. I n the author’s laboratory, following protein precipitation, the chromic acid digestion and distillation previou~lydescribed ( 2 , 9) are routinely used, while Man and associates (6) have used it following a permanganate digestion and distillation. In the chromic acid procedure, proteins have been precipitated by the use of tungstic acid. This reagent has the disadvantage of producing a precipitate of tungstic acid in the digestion flasks, but has been satisfactory in other respects.
arsenious acids may be considerably superior. I t is possible that metallic catalysts may be required for the most satisfactory reducing combination. Hydrazine has some desirable characteristics as a reducing reagent, but has given erratic results in recovery experiments. The combination of reducing agents originally recommended was phosphorous acid followed by hydrogen peroxide, which probably increased the amount of iodine present in the free state, and thus influenced the rate of distillation. Further work on the factors involved in this stage of the procedure is currently being carried on. With proper attention to the meticulous technique required and the proper purification of reagents, a consistent 90 to 95% over-all recovery of iodine by the methods described here has been obtained. LITERATURE CITED
(1) Barker, S. B., J . Bid. Chem., 173, 715 (1948). CHOICE OF REDUCING AGENTS
The problems connected with the choice of reducing agents for the digest have not been completely solved. In addition to preparing all reagents with a suitable low blank, the reduction of iodic acid and the simultaneous distillation of iodine are probably the most critical step. A suitable reducing reagent must have the right oxidation-reduction potential for both vhromic acid and iodic acid. It should not dilute the steam with noncondensable gases and should be nonvolatile itself. Phosphorous acid. which haR been most used as a reducing agent, is by itself not entirely suitable, probably because of its slow rate of reduction of iodic acid, and perhaps because of reduction to the iodide rather than free iodine. Recent work indicates that the use of both phosphorous and
(2) Chaney, A. L., IND. ENG.CHEM., ANAL.ED., 12,179 (1940). (3) Connor, A. C.,Swenson, R. E., Park, C. W., Gangloff, E. C.,
Liberrnan, R., and Curtis, G. AT., Surgery, 25, 510 (1949). (4) Greenwood, I. A . , Holdam, J. V., and Macrae, D., Jr., “Electronic Instruments,” pp. 548-67, Xew York, McGraw-Hill Book Co., 1948. ( 5 ) Man, E. B., Siegfried, D., and Peters, J. P., to be published. (6) Miiller, R. H., IND.ENG.CHEM., ANAL.ED.,11, ‘ (1939). (7) Sandell, E. B., and Kolthoff, I. H., Mikrochim. Acta, 1 , 9 (1937). ( 8 ) Sappington, T. S., Halperin, N., and Salter, W. T., J . Pharmncol. Ezpt. Therap., 81, 331 (1944). (9) Taurog, A , , and Chaikoff, I. L., J . Bid. Chem., 163, 1 (1946). RECEIVED September 20, 1949. Presented before the Division of Biological Chemistry a t the 117th Meeting of the AMERICAN CHEMICAL SOCIETY,San Francieco, Calif. Arrangements have been made with National Technical Laboratoriee for production of additional models of this recording colorimeter.
Determination of Milligram Quantities of Vanadium in the Presence of Uranium R. H. GALE AND EVE MOSHER Knolls Atomic Power Laboratory, General Electric Company, Schenectady, N . Y . An improved method for the determination of milligram quantities of vanadium in the presence of uranium is described. Use of a modified dead-stop procedure and a weight microburet increases the sensitivity and precision of the method. Results are given in the range of 0.10 to 4.0 mg. of vanadium.
AXADIUM in macro amounts has been determined volumetrically by a number of methods. It has frequently been separated from sexivalent uranium by a cupferron precipitation (7, f 6). Numerous spectrophotometric methods are available for determination of vanadium on a micro scale. Important among these methods are those depending upon color development as phosphovanadotungstic acid (8, f8) and as the peroxidized vanadium complex (19). The usual methods for volumetric determination of vanadium depend upon either a selective oxidation of the vanadium as in the presence of chromium or upon a complete oxidation followed by a selective reduction of the vanadium to the vanadyl state. Willard and Young ( I 7 ) determined vanadium in steel by oxidation of the sample with perchloric acid. A measured quantity of ferrous ion was added and the excess titrated with Permanganate at room temperature. Willard and Gibson (16) oxidized chromium and vanadium in ores and alloys with boiling i O % perchloric acid; the oxidizing action of the excess perchloric acid was
terminated by dilution with water. Decret ( 4 ) determined both chromium and vanadium in a single sample by a double titration with ferrous sulfate, depending upon a selective oxidation with permanganate. These volumetric titrations have been carried out potentiometrically and with internal indicators; a recent electrometric determination is that of Claassen and Corbey ( 8 ) . However, in the presence of a large excess of uranium, the colorimetric end points are somewhat difficult to determine, and the conventional potentiometric titration does not yield an extremely sharp inflection point when only 1 or 2 mg. of vanadium are present. Although vanadium is not usually determined gravimetrically, because of interferences, a microgravimetric procedure for the separation of vanadium and uranium has recently been reported by Kroupa (10). A rapid method for the direct determination of milligram quantities of vanadium in the presence of a large excess of uranium utilizes the reduction of quinquevalent vanadium to the vandyl ion by ferrous ammonium sulfate (8, 11). The accurate
V O L U M E 22, NO. 7, J U L Y 1 9 5 0
6
I
943
\ I
of titrant by its vanadium titer gives mass of vanadium present.
ANALYTICAL CHEMISTRY
944
Table 111. Vanadium Analyses in Presence and Absence of Uranium Aliquot
Soh.
1
V Present
11.11.
.lly.
1.00
1.78 3.56
2.00 3.00
S o h . L' 3.00 2.00 1,00 0.500
0.300 0.200 0,100 0.060
5 ,:34
No. of Detns.
V Found, h'o Cranium
v Follnd, Grains U Preaent
$
xg. 1.78 ?.52
XO.
3 2
3
1.78 :I 5 2 3 34
1-1.5
S o . of Detm.
3
J
33
Standard Deviation
% ,... . . , .
,
the vanadium is necessary, because the iron present from the initial titration does not cause difficulty.
SiIsxirn~ini Deviation
74 ..,
..
ACKNOWLEDGMENT
The authors acknowledge the helpful suggestioris of L. P. Pepkowitz and of E. L. Shirley with regard to use of the microburet.
1 3 Grains
U Present
n
3.62 2.41
, .
1.21
0.60 0.36 0.24 0.12 0.07
.. , .
..
5 3 1
h
3 3
3 63 2.43 1.20
0.fil 0.36 0.25
0.10 0 . (18
ri 23
0.4i 0 . 3$1 0.i4 1 2
1.6
.. ..
0.31 0.58
0.74
LITERATURE CITED
(I) Boaz, S u m e r o f . P r o t a t a , a n d Throckniorton,
"Chemical and Spectrochemical Analysis of Uranium arid Plutonium Materials," Atomic Energy Commission, DccZassi$ed Document .. MDDC 279 (194G). .. (2) Claassen aiid Corbey. Rec. t m o . chim.. 67, 5-10 (1948). ( 3 ) Cooper and )Tinter. :iN.IL. (:HEM., 21, 6Oj (1949). (4) Decret. Anal. Chinz. Acta,, 1, 135-4 (1947). (5) Foulk a n d Rawden, .J. Am. Chern. SOC.,48, 2045 (1926). (6) Furman, Ibid., 50, 1675 (1928). (7) Hillebrand a n d Lundell, "Applied Inorganic Xiiaiysis." p. 61, New York, John .\Viley & Sons, 1929. (8) Kolthoff and Yandell, IND.ERG. & m . . ANAL. Eu., 2, 140-5 (1930). (9) Kolthoff and Toinicek, Rcc. t m i i . chinz., 43, 447 (1924). (IO) Kroupa, Edith, M i k r o c h e m i ~W T . M i k ~ o c h i r n . Acta, 32, 245-51 (1944). (11) Lang and Kurz, 2. mad. Chem., 86, 288-:103 (1931). (12) Mitchell a n d Smith, "Aqunmetry," 11. 86, Kew York, Int,erscience Publisbcrs, 1948. (13) Pepkowita and Shirley, grivat,e cooiniunication from L. P. Pepkoivi tz. (14) Stock, Metnllurgia, 37, 220-3 (1948). (15) Strock and Drekler, .I. O p t i (16) Willard and Gibson. ISD. 1.. E D . , 3, 85-93 0 85 1 3 2 0
~I
of the potentiometric method compared favorably with the deadatop procedure; however, the rapidity and ease of the dead-stop procedure have much in their favor, especially in the presence ol' excess uranium. In Table I1 are show11 data for recoveries of vanadium in the presence ol 10 mg. of chromium and 10 mg. of t,it,a.niumas ivcll as excess of uranium. These elements are t,wo that frequently occur in Janiples analyzed for vanadium. It is apparent that as much as 10 mg. of chromium or titanium will not interfcre in t,hc determination of milligram quantities of vanadium. Table 111 contnins data for recovc:ics oC vnnadium in the mngc of 5 to 0.10 mg. The largest single i l tion has n value of -I.S", u-hcn 0.44 mg. of variadiunl is prescnt. Iri the usual sample cont.aining approsimatcly 2 mg. of van:ltliurn, the niilrimunl tiwintion was less than 0.67, arid the average deviation in several samples will be considerably less than thjs?:tmount. When this deviation is considered in terms of a sample containing an escess of uranium, the result is much better than can be utilixed. The method is applicable to the usual source materials containing vantttiium arid uranium and to samples corit,aining no uranium. One sample may be run several times by this method: only a reosidat,ion of
(1931). (17) Willard and Young, I h ' d , 6, 48-51 (19314). (18) Wright and Mellon, I?>id.,9, 251 (1937). (19) Ibid.. p. 375. RncEIvsn Se[!telnher 29, 1949 W o r k rsr:ied Eng. 52, Atoiiiic Energy Commission.
olit
iinder contract 1$'-31-109
Separation and Determination of Cobalt in Presence of Nonvolatile Radicals Use of Quuternury Ammonium Hydroxides LOUIS C. W. BAKER A Y D TIIO.1;IAS P. h1CCUTCHEO.V University of Pennsylvania, Philadelphia, Pa. OBALT may be weighed accurately as cobalt sulfate followC ing ignition a t not over 550" C. When only volatile or ashless ions or molecules are present, cobalt may be deter( 6 , ?).
mined by evaporating to dryness with a little sulfuric acid and igniting (6). When nonvolatile radicals are present, cobalt is frequently separated by precipitation with a strong base and an oxidizing agent. Because the precipitated cobaltic hydroside always occludes some of the alkali (4)and some of the other nonvolatile component,s of the solution, high results are obtained if the cobaltic hydroside, even though very thoroughly washed, is converted to cobalt sulfate for weighing. The procedures available for accurately estimating cobalt in these cases involve special equip-
ment or techniques which lack the simplicity and elegance of the sulfate method. The purpose of this paper is to show that by substitut,ing the readily available, strong, ashless quaternary ammonium hSdroxides for the alkalies, precipitates are obtained which can be converted quantitatively to the sulfate for accurate weighing. When nonvolatile constituents are present,, the cobaltic hydroxide must be dissolved again and reprecipitated to avoid occlusion of traces of nonvolatile substancrs. Sodium hydroxide may be used for the first precipitation. Bromine water may not be used as the oxidizing agent in the precipitation with the quaternary ammonium hydroside, because these reagents form orange precipitates, probably perbromides ( 2 ) ,when mixed.
