V O L U M E 26, NO. 8, A U G U S T 1 9 5 4
1361
Based 011 this equation, each set of equilibrium values of raffinate and extract concentrations was used to calculate the per cent efficiency of the 12-stage bank corresponding to that particular set of conditions. These results are summarized in Table V, and presented in graphical form in Figure 9. T h e efficiency is seen to be a function of total flow rate to the bank and is independent of flow ratio or solute within these limit.. The AlcCabe-Thieltype diagrams (Figures 5 and ;I) indicate that e q u i l i b r i u m was generally established in each stage of the bank for both runs shown, as the stage data fall on the k50 theoretical equilibrium FLOODING line in each case. Losses 33 in bank efficiency were , , , apparently due to poor L settling and resultant 10 20 30 40 50 TOT4L FLOWRATE TO BANK j c c l m l n ) back-mixing, a s i n d i Figure 9. Relationship becated by the position of tween Bank Efficiency and some of the stage operatTotal Flow Rate to Bank for ing points above the All Runs operating line. In the X Phenolrun second aniline r u n , 0 Anilinerun where the total flox rate was increased to flooding, the bank became hych u l i c a l l y inoperable a t a flow rate of
Such visual evidence of back-mixing would tend to confirm the belief, based on the stage data and operating points, that the loss in theoretical stages was due not to inefficient mixing, but to poor settling a t the higher throughput rates. Relatively simple stage modifications, such as increasing the size of the settling section or the size of the light phase port, should permit high efficiency operation a t much higher flow rates if this is desirable. The miniature mixer settler has shown high efficiency and operability with systems other than those reported on in detail here. At moderate floiv rates and with systems having reasonable settling properties, consistent performance of the unit at 85 to 95% efficiency may be expected. For those interested, complete production blueprints of the unit are available from this laboratory.
I
,I
:‘il
aqueous droplets, resulting from inadequate settling.
ACKNOWLEDGMENT
The special assistance and advice of B. I-.Coplan, \I-.0. Haas, and E. L. Zebroski are gratefully acknowledged. LITER4TURE CITED
(1) Barson, K.,and Beyer, G. H., Chem. Eng. Piogr.. 49, 243 (1953). (2) Coplan, B. V., Davidson, *J. K., and Zebroski. E. L., Ibrd., t o
be publiahed. (3) Craig, L. C., and Craig, D., “Technique of Organic Chemistry,” ed. by A. Weissburger, Vol. 111. Chap. IV, Kew York. Interscience Publishers, 1950.
for the
L- S Atomic Energy Commission
Anodic Polarographic Wave of Vanadium(lV) Aged in Alkaline Solution I. M. K O L T H O F F and P A U L T. TOREN School o f
Chemistry, University
of Minnesota,
Minneapolis, M i n n .
T
HE oxidation of vanadium(1V) at the dropping mercury electrode has been studied by Lingane and l\leites ( 1 ) . They found a single reversible wave With half-wave Potential of -0.432 volt versus the saturated calomel electrode, and a diffusion current const,ant, I ( = id/cm.2’3t1”3) of - 1.466 in s o h tions w7hichwere i A ~ in1sodium hydroxide and 0 . 0 8 ~ 1in sulfite. As the free alkali was decreased, the half-wave potential became more positive, while the diffusion current constant remained about the same. I n solutions 0.25X or less in sodium hydroxide, the>-found that the single reversible mrave ,,hangeti to two irreversible waves, which \vas ascribed to the presence of tn-o vanadite ions, V40s--and V205--. In theauthors’ polarograrhic st,udy of the system they obtained results in full agreement with those of Lingane and Meites. It was noted, however, that the irreversible double viave obtained in solutions 0.25M or less in sodium hydroxide changed to a single wave when the solutions were aged before measuring the currentcvoltage curve. Cionsequently, some experiments on the effect of aging on the anodic wave of vanadium(1T’) in alkaline medium were performed. EXPERIMENTAL
Standard vanadyl sulfate solution was prepared by dissolving Fisher reagent grade VOSO4.2HZO in 0.1M perchloric acid. The solution was standardized by potentiometric titration with ceric sulfate in 3M perchloric acid. Current-voltage curves of aged vanadium(1V) solutions were
measured in solutions of varying pH. Fifty milliliters of a buffer solution of alkalinity ranging from pH 9 (ammonia buffer) to 0.5M sodium hydroxide was placed in a screw-cap bottle sealed with a neoprene gasket and all oxygen removed b), bubbling with pure nitrogen for 1 hour (with ammonia buffers the nitrogen was prewashed with the same buffer in several wash bottles). The solutions were made up t o an ionic strengt’hof 0.5, by the addition of sodium perchlorate where necessar Then 5 ml. of air-freP o,015L~1 vanadyl sulfate solution (o,l in perchloric acid) lvv:t$ inserted through the gasket into the solutiorl with a hypodermic syringe. The mixture was well shaken and allowed to stand for several days t o allow the establishment of equilibrium. The current-voltage curve of the aged solution \vas measured by flushing out a closed polarograph cell Tvith nitrogen for l 5 arid then forcing the solution from the sealed bottle into the cell by means of nitrogen pressure through t,wo 6-inch needles connected by Tygon tubing. A flow of nitrogen was maintained through the polarographic cell while the solution was being transferred. Thc current-voltage curve at the dropping mercury electrode ~~a~ then measured manually, after which the pH of the solution measured. RESULTS
The current-voltage curves showed a single anodic mvc. throughout the p H range. The half-wave potential and diffuare given in Table I, as as values sion current the quantitY E3/4-E1/4. This quantity is equal to 0.056/n at 25” C. if the polarographic wave is described by the equation: = El.2-(0.059/n)log i/(id - i), and is thus a criterion of
1362
ANALYTICAL CHEMISTRY
Table I. Polarographic Characteristics at 25" C. of Anodic Vanadite Wave after Aging in -4lkaline Medium Electrolyte
PH 9.1 10.1
Eiiz ( m . S.C.E.) -0.25
10.5
10.7 10.9 12.1 12.4 12.6 12 8
13.7 (calcd.)
-0.34 - 0 34 -0.39 -0.42 -0.42 - 0 42 -0.37
-0.38 -0.42
1
-1.12 -1.06 -1.1 -1.02 -1.02 -0.83
-0.75 -1.01
-1.11 -1.11
O'Oi5 0.05 0 06
from 13.7 to 10 and are of the same order of magnitude as those reported by Lingane and Meites. For the diffusion current constants, values of -1.466 to -1.41 were reported in unaged solutions compared to values of -1.1 and less observed in aged solutions. The decrease in the diffusion current constant throughout the pH range in aged solutions, as well as the disappearance of the double waves, suggested that a slow association process takes place in alkaline solutions of vanadium( IV).
(0:Oi) 0.065
...
the reversibility of the wave ( 2 ) . The values of E314 - Elir given in the table indicate that these anodic waves may be considered reversible as far as the criterion is concerned.
ACKNOWLEDGMENT
The work was carried out in a test of the possible replacement of iron( 11) by vanadium( IV) in low temperature polymerization recipes under the sponsorship of the Reconstruction Finance Corp., Office of Synthetic Rubber, in connection with the synthetic rubber program of the United States Government. LITERATURE CITED
DISCUSSION
The half-wave potentials in the aged solutions vary only slightly between -0.42 and -0.34 volt when the p H is decreased
(1) Lingane, J. J., and Meites, L., J. Am. Chem. SOC., 69,1882 (1947). (2) Tomes, J., Collection Czechoslov. Chem. Communs., 9,26 (1937). RECBIYED for review March 18, 1954. Accepted May 5, 1954.
New Solvent System for Separation of Amino Acids By Paper Chromatography R. A. CLAYTON'
AND
F. M. STRONG
D e p a r t m e n t o f Biochemistry, University o f Wisconsin, M a d i s o n 6, W i s .
D
C R I S G purification studies on a plant growth factor from coconut ( 5 ) , fractionation progress was followed by paper chromatographic resolution and detection of the ninhydrinpositive components of the various concentrates. The more common solvent systems available for the separation of ninhydrinpositive materials were found to be unsatisfactory for this work. Consden at al. ( 3 ) and Block et al. ( 1 ) describe the use of various phenolic, organic base (both buffered and unbuffered), and butyl alcohol solvent systems. The phenolic systems were found to be undesirable for routine work because of their corrosive nature and because they are generally equilibrium systems, the composition of which is affected markedly by temperature fluctuations. The common n-butyl alcohol-acetic acid system (1) was found to be unsatisfactory because of the slow movement of the solvent front after several hours of development. Since the decrease in ~olventfront movement was accompanied by the development of the odor of ethyl acetate in the chromatographic chamber, tertbutyl alcohol was substituted for n-butyl alcohol in an attempt to reduce esterification. While this substitution did decrease esterification, and enhance the solvent front movement, the resolution of the ninhydrin-positive components was greatly impaired. The high cost of organic bases such as lutidine and collidine renders these solvents impractical for daily, routine investigations. The new system, which has been used successfully in this laboratory for the resolution of ninhydrin-positive compounds, consists of methyl ethyl ketone, propionic acid, and water in the volume ratios 75 :25 :30. The solvents are completely miscible and hence the composition of the system is not altered by temperature fluctuations. The solvent front moves about 40 cm. in 20 hours on ascending chromatograms, and can be air-dried in 30 minutes to allow spraying with a butyl alcohol solution of 1 Present address, Department of Biochemistry, George Washington University, Washington, D . C.
ninhydrin. The movement of 24 amino acids has been studied and the R, differences among the individual amino acids have been found to be as great as those reported with any of the existing unidirectional systems. Replirate R , determinations were found to agree within f 2 % . In application to natural produot work in this laboratory, this solvent system has allowed resolution of eight ninhydrin-positive spots in a unidirectional chromatogram of an acid hydrolyzate of a purified coconut meat fraction (2). In another experiment, this same hydrolyzate were resolved further into 12 spots by development of the chromatogram with the same solvent system in a second direction. This new solvent system can be used for routine, unidirectional paper chromatograms of amino acids, or in combination with one of the published systems for two-directional chromatograms where the separation of complex mixtures of amino acids or peptides is desirable. EXPERIMENTAL
Preparation of Samples. Solutions of 24 amino acids (Table I ) were prepared by dissolving a p rovimately 20 mg. of each amino acid in 1 ml. of L O N hydrocfloiic acid and diluting to 10 ml. with water. These solutions were kept frozen when not in use. Asparagine and glutamine gave two ninhydrin-positive spots 2 weeks after preparation of the solutions. This observation seemed to indicate partial conversion to the correspondingdibasic acids. Operating Procedure. Whatman No. 1 sheets (46 X 52 cm.) were used as supplied by the manufacturer throughout this work. Two to 4 Y of each amino acid were applied to the Paper on the base line at points 1.5 cm. apart. Ascending chromatograms were run with a solvent system which consisted of 75 ml. of methyl ethyl ketone, 25 ml. of propionic acid, and 30 ml. of water. The pa ers were run for 20 hours in a Chromatocab (Model A, Researci Equipment Corp., Oakland, Calif.) a t 22' to 24' C. The solvent front generally moved about 40 cm. during this period of time. After 20 hours, the papers were removed and air-dried for 30 minutes. The papers were sprayed with a butyl alcohol solution of ninhydrin (0.125%) which contained one crystal (5 mg.) of
