85
V O L U M E 20, NO. 1, J A N U A R Y 1 9 4 8 (3) Jones, J. H., J . Assoc. Oficial Agr. Chem., 26, 182-6 (1943). (4) Lee, S. W., Wallace, J. H., Jr., Hand, W. C., and Hannay, K.B.. ISD. ENO.CHEM.,-4x.4~.ED.,14,839 (1942). ( 5 ) Mahoney, J. F., and Michell, J. H., I b i d . , 14, 97-8 (1942). (6) Manov, G . G., and Kiik, P. L., I b i d . , 9, 198 (1937). (7) Schroeder, W. C., Ibid., 5,403 (1933). ( 8 ) Sheen, R. T., and Kahler, H. L.. I b i d . , 8 , 127 (1936).
(9) (10) (11) (12)
Ibid., 10, 206 (1938). Sheen, R. T., Kahler, H. L., and Cline, D. C., Ibid., 9, 69 (1937). Sundberg, 0. E., and Royer, G. L., Ibid., 18,719 (1946). Wilson, C. W., and Kemper, W. A , , Ibid.. 10, 418 (1938).
RECEIVED M a y 15, 1947. Presented before t h e Division of Analytical a n d Micro Chemistry a t the 111th XIeeting of t h e Atlantic City, S . J .
. ~ M E R I C . A Z ICHEMICAL SOCIETT,
Microvolumetric Method for Determination of Sulfur in Organic Compounds .
JOSEPH F. ALICINO Squibb Institute f o r Medical Research, .Yew Brunswick, 4.J .
A rapid microvolumetric method for determining sulfur in organic compounds has been developed which gives a sharp end point reproducible to within 0.05 ml. and requires no blank correction within the usual ranges.
IT11 the discovery in recent years of a n increasing number >f biologically important substances which contain sulfur, there arises a need for a rapid method for the determination of this element. Many volumetric methods ( 2 ,,5, 7 ) , both direct and indirect, have been proposcd to accomplish this end but of these thc most promising appear to be procedures using tetrahydrosyquinone or rhodizonates ( 4 , 8 , 9 ) . While some difficulty has been experienced by some ( 1 , 3, 6 ) in obtaining satisfactory end points with this indicator, the simplicity of the method seemed to warrant further investigation. It was felt that greater simplification, especially with the view of eliminating the necessity for using elaborate or special equipment, might render the method more popular, particularly with academic institutions. A simple determination of sulfur was proposed by Brervster and Ilieman (a),in which the sulfuric acid formed by combustion is titrated after the volatile acids have been removed by evaporation over the steam bath. This method can be made to yield reliable results only when certain conditions, sometimes difficult to control, are adhered to. As mentioned by Brewster and Rieman and confirmed in this laboratory, variable factors such as the alkalinity of the spiral, length of time of evaporation, rate of fioiv of air, etc., influence the blank. I n this laborat.ory, the blank corrections mere someyhat larger than espected. This was attributed to the difficulty of completely removing animonia from the air system. Consequently, i t seemed feasible to use a sulfate titration to aroid the errors mentioned aborc. No advantage was gained by using the method of Ingrani at this point, since i t is esseiitially aikalimetric. lieliable and consistent results were obtained after sonic invrstigation, wing tht. proposed procedure.
0.2- to O.4-mg. of dipotassium rhodizonate vias ad1 . (preferably from the tip of a microspatula) and a fairly rapid, drop-by-drop addition of the barium chloride solution mas continued until about 9 0 5 (as measured by the alkali consumption) was reached. At this point, the color was still yellow and as more barium chloride was added a cherry-red coloration began to appear and was dispelled by agitation. The time interval between drops was increased to alloiv more thorough shaking, so t h a t the fleeting red coloration could be entirely dispelled before addition of the next drop. The end point is reached when the red coloration persists after vigorous swirling for 30 seconds.
Table I.
Determination of Sulfur Per Cent Siilfur
Compound hI ethionine Thiourea Thiocarbanilide Cystine Sulfanal Benzylpenicillin Cpd. C H S O S
Cpd. C H B r S S Cpd. C H I N O S Streptarnine sulfate
Found 21.39 21.31 42.33 42.12 14.01" 26.61b 27.92 27.94 8.89 9.04 18.95 18.52 11.48 11.33 8.39 8.52 l'.?$C
Theory 21.49 42.12
14.03 2S.69 28 09 8.99
18.32 11.44 8 . 33 11 . G O
1 1
Il.Il
0.98 0.97 sulful 99.82 99.77 a Xveraeeof 12analvses: max. 14.18. rnin. 13.88. b Averale of 10 anal3ses: max. 26.78, min. 26.47. Sample titrated directlywithout combustion. d rlverage of gravimetric analyses 0.98. Protein
0.98.r 100.00
PROCEDURE
The usual Prcgl method n-as followed n-ith certain modifications. Platinum wire gauze (14 cm. long) n-as substituted for one of the contacts because it ensured a longer and more complete contact of the osidation products with the catalyst in substances which have a tendency to volatilize rapidly. Oxygen was delivered from a gasometer without drying and passed through a bubble counter containing water alone, since watersaturated oxygen appears to minimize sulfur trioside mist ( 5 ) . After the combustion of the sample was complct,ed, the rinsed spiral contents were evaporated as directed by B r e m t e r and Rieman, escept t h a t with a rapid current of air over the steam bath only 30 minutes were found necessary. Standard 0.01 LVsodium hydroxide was added from a buret directly into the evaporating dish until a pink coloration was produced with phenolphthalein. After transfer to a 50-ml. Erlenmeyer flask, the rinsing was accomplished by adding a n equal amount of 95% ethyl alcohol. hpproximately half of the equivalent amount of 0.01 N barium chloride solution could be quickly run in with shaking. About
Under the above conditions, the end point can be made reproclucible to within 0.05 ml. without much practice and does not require a blank correction mithin the r a n g e of the usual determination. The adoption of the evaporation procedure greatly increases the sharpness of the end point and improves the method. Elimination of extraneous anions results in a n ideal solution of sodium sulfate. The use of hydrogen peroxide solution, which is both a convenient absorber and satisfactory oxidant, is possible. The barium chloride addition is better cont.rolled, especially with compounds of unknown sulfur content, by virtue of the predetermined alkali value. The sharpness of the end point is such that no color comparison is necessary.
ANALYTICAL CHEMISTRY
86 The method was used for two years on several hundred compounds. Table I gives typical results on subtances of known purity. LlTERATURE CITED
(1) Ampt, G. A , , Australian Chem. Inst. J . Proc., 2, 10 (1935). (2) Brewster and Rieman, IND.ENG.CHEM.,.ISAL. ED., 14, 820 (1942). --, (3) Gibson, D. T., and Caulfield, T. H . , A n a l & 60,522 (1935). (4) Hallett, L. T., and Kuipers, J. W., IXD.ENG.CHEM.,A X I L . ED., 12,360 (1940). (5) Ingrani, G., A n a l y s t , 69,265 (1944). \
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Mercury Slug Flowmeter K. L. YUDOWITCB Gniversity of Missouri, Columbia, .llo.
C I D E X T A L t o other researches for the l I a n h a t t a n Pioject, I Sthe author developed \vith J. F. Bacon and othei associates a
(6) Manov, G. G., and Kirk, P. L., ISD. ENG.CHEM.,ASAL. ED.,9,
198 (1937).
( 7 ) Niederl, J. B., and Niederl, V., “Organic Quantitative Microanalysis,” 2nd ed., pp. 190-6, New York, John Wiley & Sons,
1942. ( 8 ) Ogg, C. L., Willits, C. O., and Cooper, F. J., A s a L CHEM.,20.,
83 (1948). (9) Sundberg, 0. E., and Royer, G. L., IKD.ENG.CHEM.,ASAL. ED.,18, 719 (1946). RECEIVEDJune 9, 1947. Presented before the Division of Analytical and Micro Chemistry a t the 111th Meeting of the AMERICASCHLYICAL SOCIETY, Atlantic City, N. J.
of a relay activated by the paasiage of the slug past the contacts shown in the illustration. This type of meter operates over a broad pressure range (2 t o 76 em. of mercury) and on a low pressure drop (2 t o 3 mm. of mercury). Its operation is independent of the physical properties of the gas being measured. It gives a n integrated or average flow rate rather than a n instantaneous rate. The advantages of this specific design are compactness, ruggedness, and higher flow rate attainable. More than a dozen of these meters have been used satisfactorily at SA11 Laboratories. They have held their calibrations t o ri-ithin from 1 t o lo%, over several months of regular use. AIost variations were probably due t o contamination of the mercury.
meter t o measure small gas f l o w a t various pressures. The iequirements of a n operating pressure drop of less than 3 mm of mercury and independence from t h e physical properties of the gas made capillary flowmeters, rotameters, and circuit-terminating flowmeters undesirable. Various designs of absolute displacement meters were investigated. Marsh’s ( 2 ) original design based on the displacement of a LITERATURE CITED bubble of amyl phthalate between scratches on a straight capillary (1) Appleby, IT. G., and Aver>-,W.H., IND.ESG. CHEY.,A s a ~ ED., . tube appeared unsatisfactory for several reasons. The range 15, 349 (1943). quoted was 0.25 t o 1 cc. per minute, much below requirements. (2) Marsh, ALE . L.. Trans. Faraday Soc., 36, 626 (1940). T h e accuracy of a straight tube meter varies as the distance beRECEIVED June 11, 1947. Based on v o r k performed under contract No. t w x n scratches, requiring a tube several feet long for reasonable. K-7405-eng-26 for the Manhattan Project. T h e information will appear in accuracy. Division VI11 of the Manhattan Project Technical Series a s p a r t of the Appleby and Avery ( 1 ) substituted mercury for amyl phthalate, contribution of the S;iM Laboratorieu, Carbide and Carbon Chemicals permitting the use of larger tubing and consequently higher flow Corp , New York, N. Y. rates. The range (up t o 25 cc. per minute) was still low and the delicacy of design incompatible with the need for portability a n d ruggedness. I n operation the mercury slug continuously ,--BYPASS traverses the spiral path as indicated. The spiral is made by winding 6-mm. Pyrex tubing in a plane, and allowing it t o set on a slightly convex carbon block. This fixes t h e spiral outlet 1 t o 2 mm. above the inlet. Sufficient mercury must be used in the meter, so t h a t a new slug will close the spiral entrance before the original slug completely leaves the spiral. The length of t h e slug and therefore t h e volume swept out per cycle were found t o vary somewhat with flow rate. This necessitates calibration over the range of flow rates t o be encountered. Below rates of about 25 cc. per minute, the volume swept out increases anomalously. I t is suggested t h a t the spiral be made of smaller tubing if it is desired t o measure rates below 25 cc. per minute. With the simple precautions of cleanliness and careful l e v e h g , rates of over 250 cc. per minute Tvere attained before the slug broke into several sections. It is not feasible t o use tubing much MERCURY SLUGlarger t h a n 6 mm., as the mercury will not then MERCURY WELLI ’ form a slug. The cycles may be counted by means
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