ANALYTICAL EDITION
September 15, 1941
TABLEv. COMPARISON OB STkVD.4RD DEVIATIONS O F RESULTS OBTAINED BY AZIDE AND SULFAMIC ACID MODIFIC.4TIONS O F WINKLER METHOD No. of
Samples in Series
Samples Ohio River and tributaries Raw sewage dilutions Trickling filter effluent dilutioni Activated sludge effluent dilutions Combined
Standard Deviation Initial Final dissolved dissolved Oxygen oxygen oxygen depletion P.p.?n. P.p.m. P.p.m.
322 119 121
0.070 0.073 0.052
0.12
0.15
0.14 0.19 0.16
90
0.047
0.15
0.16
652
0.065
0.18
0.14
0.16
liminary treatment for the removal of nitrites in the dissolved oxygen determination is as satisfactory as the azide modification for the determination of dissolved oxygen and biochemical oxygen demand in sewagetreatment and rirerpollution studies.
625
The two modifications, azide and sulfamic acid, appear to have equal value in the prevention of biochemical oxidation when it is necessary to store a dissolved-oxygen sample for a short time.
Acknowledgment The authors wish to acknowledge the assistance of Oliver
R. Placak in the analytical work and R. S. Smith in preparation of Figure 1.
Literature Cited (1) (2) (3) (4) (5) (6)
Barnett, G. R., and Hurwitz, E., Sewage Works J.,11, 781 (1939). Baumgarten and Marggraff, Ber., 63,1019 (1930). Cupery, M.E., IND. EXG.CHEX.,30, 628 (1938). Gordon, W. E., and Cupery, M. E., Ibid., 31, 1237 (1939). Hahn and Baumgarten, Ber., 63, 3028 (1930). Placak, 0. R., and Ruchhoft, C. C., IND. ENG.CHEM.,ANAL.ED.,
13, 12 (1941). (7) Ruchhoft, C. C., Moore, W. A,, and Placak, 0. R., Ibid., 10,701 (1938). PRESENTED before the Division of Water, Sewage, and Sanitation Chemistry a t the lOlst Meeting of the American Chemical Society, St. Louis, Mo.
Polarographic Determination of Ascorbic Acid MARY MA”
F
KIRK, N. Y. State Agricultural Experiment Station, Geneva, N. Y.
S
INCE polarographic analysis is essentially based on current voltage curves and ascorbic acid is a reducible electrolyte, this method seems suitable for vitamin C determinations. The determination is not hindered by the presence of pigments, it is specific, and it is sensitive to small amounts of electrolyte. Very complete discussions have been published by Kolthoff and Lingane (4)and Muller (6). Preliminary vitamin C determinations were made with a Fisher Elecdropode ( 2 ) or polaro6raph. To run a determination, the beaker containing the solution t o be analyzed is placed under the dropping mercury electrode. About 5 mm. of pure mercury are placed in the bottom of the beaker t o act as the quiet mercury electrode and the platinum anode contact is immersed. Nitrogen is then passed through the solution as a steady stream of bubbles. This is continued for 15 minutes in order t o eliminate any dissolved atmospheric oxygen, which might interfere with the curve, since it is easily reduced at the dropping electrode. Just before starting the determination, the nitrogen is started flowing across the surface of the solution instead of through it. If the gas is not thus cut off, fluctuations occur in the curve. During the determination the rate of dropping of the mercury should be kept at one drop every 3 t o 6 seconds, if accurate results are t o be expected. Too slow dropping causes slow oscillations in the polarogram and instability in the record. Too fast dropping produces undesirable agitation and mixing effects in the surrounding electrolyte. The dropping rate can be adjusted by changing the height of the mercury reservoir attached to the electrode. Kodicek and Wenig (3) suggested the use of a 0.067 N phosphate buffer and used the dropping mercury electrode polarized as a n anode in the determination of vitamin C on the polarograph. Since 2 per cent metaphosphoric acid has been found very satisfactory as a n extractant, work was started using it as the base solution in the determination and very satisfactory curves were obtained (Figure 1). One to 3 cc. of an ascorbic acid solution, which was approximately 0.001 N , were added to about 50 cc. of the base solution. Curves were drawn using the dropping mercury electrode both as the anode and as the cathode. No very sharp rise was noted when the electrode was polarized as the anode; however, on one set of curves there did seem to be a very definite rise a t about +0.33 volt, which was in the vicinity
of that noted by Kodicek and Wenig. The difference in height caused by varying concentrations was slight even on this curve. A much sharper drop occurred a t -1.77 volts. This reading was constant, varying not more than *0.05 volt for all the curves run. Since 0.067 N phosphate buffer a t p H 7 had been suggested, this, an acetate buffer of pH 2.2, and a potassium acid phthalate-hydrochloric acid buffer of pH 2.2 were also tried, but none gave very consistent results. The phosphate buffer gave a rise which was not typical; the acetate buffer caused too rapid dropping of the mercury as the voltage rose and the half-wave potential came a t decreasing voltages with increasing ascorbic acid concentration; the potassium acid phthalate-hydrochloric acid buffer resulted in pronounced maxima and the rise caused by the buffer occurred a t the same voltage as that caused by vitamin C. As this was the only base solution causing maxima, no precautions were taken for their prevention. A 5 per cent sulfuric acid solu-
I-
-3
-2
-I
0
VOLTS
I
2
FIGURE1. POLAROGRLPHIC CURVE
3
626
INDUSTRIAL AND ENGINEERING CHEMISTRY
tion mas tried as base solution, but increased the rate of flow of the mercury drops to such a n extent that no readings could be made. Since each compound results in a characteristic rise a t a specific voltage with the use of the proper base solution, the interference of such substances as cystine and glutathione would be eliminated. The acid base solution used for this ascorbic acid determination inhibits the production of current rises by these compounds. They are determined polarographically in ammoniacal solutions of cobaltous chloride in ammonium chloride (1). Since this work was only preliminary, no quantitative determinations of ascorbic acid were run. However, results obtained indicated that this method could be adapted for accurate quantitative analysis by comparing the curves obtained when an unknown solution mas used with calibration curves.
Vol. 13, No. 9
Acknowledgment The author is indebted to C. G. King of the University of Pittsburgh for assistance and guidance during the investigation and to the Buhl Foundation for a research grant which made the investigation possible. The investigation mas carried out on an Elecdropode kindly supplied by the Fisher Scientific Company.
Literature Cited (1) Brdicka, R., CoZZ. Czech. Chem. Commun., 5, 112-28, 148-63 (1933). (2) Fisher Scientific Co., Laboratory, 10 (9,97 (1939). (3) Kodicek, E., and Wenig, K., Nature, 142, 35 (1938). (4) Kolthoff, I. M., and Lingane, J. J., Chem. Rev., 24 ( l ) ,1 (1939). ( 5 ) Muller, 0. H., Ibid., 24 ( l ) , 95 (1939). APPROVED by the Director of the Kew York State Agricultural Experiment Station for publication a8 Journal Paper 391.
A Simplified, Water-Jacketed, Fraction Receiver R. S. TOWNE, E. E. YOUNG, AND L. T. EBY University of Notre Dame, Notre Dame, Ind.
W
ITH the development of precision fractionating columns for use under reduced pressure has come a need for a receiver which will permit a n indefinite number of fractions to be obtained without disturbing the pressure within the still. The older types of vacuum receivers, such as the Bruhl receiver, and the many varieties of multiple rotating receivers (2) are inadequate since the number of fractions which may be obtained with them is strictly limited. Several variations of the Thorne (4) distillation triangle are described in Morton ( g ) , some of them very satisfactory. Cloke ( 1 ) has recently proposed a water-jacketed modification, and Noonan (3) has designed a vacuum receiver in which the usual four two-way stopcocks have been replaced by a single multiple-way stopcock. The greatest disadvan-
tage of these receivers is that they are expensive, owing to the large number or special nature of the stopcocks required, or that they require considerable glass-blowing skill to make. The accompanying figure shows a fraction receiver which the authors developed in the organic preparations laboratory a t the University of Notre Dame. I t combines the advantages of the earlier types with greater simplicity of manufacture and operation, and reduced cost. It can be easily made by an amateur glass-blower. Only two standard 2-mm. bore stopcocks are required: a three-way T stopcock (Corning KO. 7420) and a three-way parallel stopcock (Corning KO. 7380). The cost is considerably less than that of four twoway stopcocks. The dimensions given are those which have been found most satisfactory with the ordinary laboratory stills, but a larger or smaller reservoir may be made for special work. The operation of the apparatus is simple. The sample is transferred from the reservoir of the fraction receiver to the receiver through stopcock B. B is closed and A is given a half turn, so that the receiver is disconnected from the pump but the still remains under vacuum. Air is admitted t o the receiver through B. After the receiver containing the fraction has been removed and a fresh receiver attached, B is closed and A is turned clockwise a quarter turn, so that the still is temporarily disconnected from the pump while the new receiver is being evacuated. When the correct pressure has been established in the receiver, A is turned clockwise again a quarter turn, so that the still and the receiver are both connected to the vacuum line as shown. Ground-glass joints may be used to connect the fraction receiver to the column and to the receiver, but this raises t h e cost without materially adding to the usefulness of the apparatus. A double tube may be used to connect the fraction receiver to the receiver to avoid any difficulty with viscous liquids rising in the equalizing arm, but for the most part this refinement has not been found necessary.
Acknowledgment The authors wish to thank Kenneth N. Campbell for his suggestions during the course of this work.
Literature Cited (1) Cloke, J. B., IXD. EXQ.CHEM.,ANAL.ED.,12,329 (1940). (2) Morton, A. A., “Laboratory Technique in Organic Chemistry”, p. 110, Kew York, McGraw-Hill Book Co., 1938. (3) Noonan, E., IND.ENG.CHEM.,ANAL.ED.,10, 34 (1938). (4) Thorne, L. T., Ber., 16, 1327 (1883).
