526
INDUSTRIAL AND ENGINEERING CHEMISTRY
middle of a determination. These cracks would develop at a point containing t h e silver wool (Pregl filling), which is nearest t o the combustion boat and would run lengthwise for several inches. Weakening was considered t o be caused by fusion of the silver halides (m.p. 427" to 526" C.) and sulfate (m.p. 651" C.) into the tube. Vycor tubes, made of 96'%b'silicaglass No. 790 (made by Corning Glass Works, Corning, S . Y . ) ,gave very poor results, acting like quartz, but the breakdown occurred much sooner. From a total of more than two dozen, none could be used for more than 25 combustions but the majority was worthless after 10 to 15. Tubes made of Pyrex KO.172 (made by Corning Glass Works, Corning, S.y.) (and Jena Supremax, when available) have proved the most satisfactory but these should conform t o the AMERICAN CHmr1w.L SOCIETY specifications (IO), with walls of 1.5 mm. minimum, as the regular lots of tubes are considerably thinner. The latter do not hold up as long and a comparatively large number become porous almost immediately when the filling fuses into the glass, while the heavy-walled tubes give good results for 100 t o 300 determinations. All freshly filled combustion tubes are heated in the furnace overnight with oxygen being passed through, and then tested for porosity in one of the following ways. The end of the hot tube is plugged and the bubble counter watched. If oxygen continued to pass through, even very slowly, the tube is discarded. An alternate method is to cool and disconnect the tube, stopper the end, immerse the entire length in a solution of dye such as methylene blue, and evacuate. If dye is sucked into any section, it is discarded. The evacuation and subsequent breaking of the vacuum are done very slowly, so as not t o contaminate the various sections. These tests prove many tubes t o be unsatisfactory Jvithout wasting hours of doing actual determinations TYPE O F FURNACE AND TEMPERATURE O F COMBUSTION. Furter ( 2 ) studied the effect of the temperature ofthe combustion tube on the determination, preparatory t o setting up specifications for a n electric combustion furnace. T h e temperatures a t various points in a tube heated by a Pregl gas burner were measured by thermocouples (Figure 6). An electric furnace (long burner) was then constructed t h a t had the same characteristics but whose over-all temperature could be varied. Many combustions with compounds of various types were made a t a number of different temperatures, after which Furter concluded t h a t about 670" to 680" C. was high enough for all combustions yet low enough t o prevent undue overheating of the tubes. Lower tem. peratures gave low values with a variety of substances, in disagreement with some texts which recommend a temperature of 5.50" C. for all combustions (1, 9). Obscrvations in these laborntories during the past 6 years are in agreement with those of Furter. Figure 7 shows the temperatures reached a t different parts of the combwtion tube, heated by the furnace finally constructed for Furter. The temperature gradient between the long and short burners is shown in Figure 8. This makes i t possible t o place volatile samples in the tube a t the proper point t o obtain slow distillations.
Vol. 17, No. 8
Tn these laboratories two of the Furter furnaces and two others of similar design constructed in the machine shop are used. Each is completely electrified-short movable burner, long burner, and heating mortar. i l n electric clock motor is used on each to drive the movable burners forward a t a constant rate. These motors are excellent for this purpose. Their power is adequate and their speed is low enough to make elaborate reduction gears unnecessary. The driving mechanism is comparable to ones described by other authors ( 3 , 7 , 1 1 ) who used other means of power. The combustions may be classified as semiautomatic, inasmuch as the operator keeps a close check on the apparatuq during the entire combustion, varying his technique slightly with the properties of the substance. Figure 9 shows two homemade models, while Figure 10 shows the Furter furnaces after slight modification by the mechanic. It has been found desirable to keep the furnaces hot 24 hours per day. Every morning the combustion tubes are conditioned by burning a n unweighed sample of about 6 mg. under regular combustion conditions. The setups are then ready for the day's work. Under these conditions, tubes give good results for 1 to 3 months. LITERATURE CITED
(1) Clark, E. P., "Semimicro Quantitative Organic Analysis", p. 32, New York, Academic Press, 1943. (2) Furter, M. F., unpublished, private communication from Fed-
eral Institute of Technology, Zurich. (3) Hallett, L. T., IND.ENG.CHEM.,ANAL.ED., 10, 101 (1938). (4) Hayman, D. F., Ibid., 8, 342 (1936). (5) Niederl, J. B., and Niederl, V., "Organic Quantitative Micro Analysis", 2nd ed., p. 9 , ' N e w York, John Wiley & Sons, 1942. ~. (6) Ibid., p. 136. (7) Reihlen, H., Mikrochemie, 23, 285-301 (1938). (8) Rodden, C. J.. IND.ENG.CHEM.,ANAL.ED., 12, 693 (1940). (9) Roth, H., "Quantitative Organic Microanalysis of Fritz Pregl", 3rd English ed., tr. from 4th revised German ed. by E. B. Daw, p. 38, Philadelphia, P. Blakiston's Son & Co., 1937. (10) Royer, G. L., rllber, H . K., Hallett, L. T., Spikes, W. F.. and Kuck, J. A., IND. ENG.CHEM.,ANiL. E D . ,13, 574 (1941). (11) Koyer, G. L., Norton, A . R., and Sundberg, 0. E., Ybid., 12, 688-90 (1940). (12) Van Straten, F. W., and Ehret, W. F., Ibid., 9, 443 (1937). PRESENTED before the Division of Analytical and Micro Chemistry, Symposium on Microdetermination of Carbon and Hydrogen, a t t h e 108th Meeting of the AMERICAN CHEMICAL SOCIETY, N e w York, N. Y.
Adaptation of a Color Test to Minute Amounts of Caffeine CHARLES E. MORGAN AND NICHOLAS OPOLONICK N e w York State Racing Commission Laboratory, Jamaica, N. Y.
A
VALUA13Lli: qualitative color test for caffeine is t h a t given
kvhen the drug is first oxidized and then treated with ammonia. It is analogous to the murexide test for uric acid, and, though not specific for caffeine, affords a convenient confirmatory reaction. T h c usual directions for conducting the test, however, g i v e wsults which are not sufficiently sensitive and reliable wlictii applied t o minute amounts of the drug. I n a n effort to improvo it the literature (1-18) was reviewed and experimental work done to standardize reagents and conditions for obtaining more satisfactory results.
peratures, the latter proving unsatisfactory. Heating was continued until maximum color developed, and after cooling the residues were treated with reagents to develop the final color. These were water, ammonia vapor and solution, various aliphatic amines and alkanolamines, aniline, dimethylaniline, and pyridine. For all tests 0.1-ml. quantities of solutions of caffeine monohydrate in concentrations from 1-1000 to 1-100,000 were used. Concentrations and proportions of the ingredients of all oxidizing mixtures were varied within wide limits. About 2000 individual tests were made.
EXPERIMENTAL
The best results were obtained with the following oxidizing mixtures, the amounts given being applied to 0.1 ml. of caffeine solution:
13romine water, chloramine-T, chlorine water, hydrogen peroxide, and nitric acid were the oxidants used, both with and witho u t hydrochloric acid. Hydrobromic, acetic, and formic acids were also tried but were unsatisfactory, either alone or with addition of sodium chloride. Mixtures of the oxidants with caffeine, contained in the cavities of porcelain spot plates, were eyaporated to dryness a t steam bath, hot plate, and room tem-
1. 0.1 ml. of a mixture of 9 volumes or saturated bromine water (2.8 grams per 100 ml.) with 1 volume of concentrated hydrochloric acid. 2. 0.05 ml. of a n aqueous solution of chloramine-T containing O.lSyO of active chlorine, followed by 0.05 ml. of dilute hydrochloric acid (1 plus 9).
August, 1945
ANALYTICAL EDITION
3. 0.1 ml. of a mixture of 1 volume of concentrated hydrochloric acid, 9 volumes of saturated chlorine water (0.6 gram per 100 ml.), and 90 volumes of water. 4. 0.05 ml. of 0.6% hydrogen peroxide solutibn, followed b y 0.05 ml. of concentrated hydrochloric acid. 5 . 0.05 ml. of a mixture of 9 volumes of concentrated nitric acid and 1 volume of concentrated hydrochloric acid. Any of these mixtures will give a color with caffeine in dilutions u p t o 1-20,OOO. All b u t No. 4 will give tests u p to 1-40,000, and No. 2 will give a trace of color with a 1-80,000 dilution of caffeine. T h e presence of hydrochloric a i i d appears to be essential for maximum sensitivity, whatever the oxidant used. During t h e evaporation and subsequent heating exposure to steam should be avoided, as i t was found t o cause wide variations in results. Use of a h o t plate, operating at or below steam bath temperature, IS recommended. I n producing t h e final color all the compounds tested, including water h u t excepting aniline a n d dimethylaniline, changed the colors of the residues t o a uniform purplish red, varying in persistence b u t of equal intensity, except for ammonia vapor which gave a more intense b u t relatively fugitive color. Triethanolamine is recommended since it gives a solution whose color fades very slowly, persisting for several weeks, which makes i t suitable for use in quantitative applications of the test. A mixture of equal volumes of triethanolamine and water is satisfactory. During t h e course of the work evidence was obtained t h a t losses of caffeine, significant when working with minute amounts m a y occur during evaporation of its aqueous solutions and by sublimation. For this reason heating of dry residues suspected of containing the drug should not be prolonged, and solutions should not be evaporated before adding the oxidizing mixture.
SUMMARY
-4 color test for caffeine has been investigated and standardized t o produce sensitive and reproducible results when minute amounts of the drug are present. T h e test is conducted by adding a specified amount of any one of five oxidizing mixtures t o 0.1 ml. of a caffeine solution, evaporating to dryness, preferably on a low-temperature hot plate to avoid contact with steam, continuing heating until maximum color is developed, and finally adding 0.05 ml. of a triethanolamine solution. T h e test can be made quantitative b y the use of caffeine standards because of t h e persistence of the final color produced.
LITERATURE REVIEWED
(1) “Allen’s Commercial Organic Analysis”, 5th ed., Vol. VII, Philadelphia, P. Blakiston’s Son & Co., 1929.
Autenrieth, Wilhelm, tr. by Warren, W. H., “Laboratory Manual for Detection of Poisons and Powerful Drugs”, 6th ed., Philadelphia, P. Blakiston’s Son & Co., 1928. Brunn, O.,Ber., 21, 513 (1888). Ekkert, L., Pharm. Zentralhalle, 72, 481 (1931). E’ne, G. E., and Vanderkleed, C. E., J . A m . Pharm. Assoc., 3, 1681 (1914).
Fuller, H. C., “Chemistry and Analysis of Drugs and Medicines”, New York, John Wiley & Sons, 1920. Giovanni, Issoglio, Industria chimica, 4, 458-61 (1929). Maly, R., and Andreasch, R., Monatsh.. 3, 92 (1882). Maly, R., and Hinteregger, F., Ibid., 3, 85 (1882). Miko, J. V., and Miko, S. V., Pharm. Zentralhalle, 67, 193 (1926).
Nestler. A . , 2. L’ntersuch. N a h r . Genussm., 4, 289 (1901). Rochleder, F., A n n . , 63, 193 (1847); 69, 120 (1849): 71, 1 (1849).
Rosenthaler, L., “Toxikologische Mikroanalyse”. Berlin, Gebriider Borntraeger, 1935. Schaer, E., Apoth. Ztg., 25, 705 (1910). Schwarzenbach, Z . anal. Chem., 1, 229 (L862). Stenhouse, J., Ann., 45, 366 (1843). Tunmann, O., Chem. Zefitr. 11, 42 (1919). Wende, E.. Apoth. Ztg., 34, 95-6 (1919).
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BOOK REVIEW The Analysis of Foods. Andrew L. Winton and Kate Barber Winton. 999 pages, 208 illustrations. John Wiley and Sons, Inc., New York; Chapman and Hall, Ltd., London, 1945. Price, $12.
The names of Andrew L. and Kate Barber Winton are writ large in the literature relating to the chemistry and histology of foods. The excellent teamwork which they displayed in their compendious four-volume treatise on “The Structure and Composition of Foods” is again exemplified in the present work. A companion volume dealing with the analytical methods by which the composition of foods is determined was in fact an almost inevitable consequence of their previous publication and, in accomplishing this result, the authors, drawing upon the results of their long practical experience in federal, state, and private laboratories and upon the observations of foreign study and travel, have prepared a work of inestimable value to all food chemists, whether engaged in agricultural, industrial, nutritional, and regulatory investigations, or occupied in the associated fields of biological and physiological research. Breaking loose from the restrictions imposed upon him by the long re-editing of A. E. Leach’s “Food Inspection and Analysis”, Dr. Winton in the present work found himself free to adopt an entirely new presentation of his own which is outlined on the inside of the front cover. The subject matter is divided into two main divisions: Part I (416 pages) describes the general analytical methods (microscopic, physical, and chemical) for determining (1) elementary and (2) proximate constituents of foods, including (3) water, (4) protein, (5) fat, (6) nifext (a code word for the cumbersome term nitrogen-free eztract), (7) fiber, (8) ash (including major and minor mineral elements), (9) alcohols, (10) vitamins, (11) natural and (12) artificial colors, and (13) chemical preservatives. Part I1 (530 pages) describes the special analytical methods for each of the 12 classes of food products: A cereals, B fats, C vegetables, D fruits, E sugars, F alcoholics, G dairy products, H animal foods, I alkaloidal products, J food flavors, K leaven, L salt. Running heads on each page, indicating class, group, and subdivision, assist making cross references within the book. Full bibliographic references a t the end of each section indicate original sources of information. Economy of space is achieved by a double-column arrangement of the text. While every food analyst has his own preferences as regards general and special schemes of analysis, the selections described by the Wintons represent a wide liberal choice of the best available methods; among them are many that have been tested and approved by the Association of O5cial Agricultural Chemists, in the affairs of which Dr. Winton, as a former president and executive, took a prominent part for many years. As for their choice of methods the authors remark in the preface: The analysis of methods has demanded quite as much attention some cases almost hopeless-task of the compilers has been the separation of the method proper from its entanglement with experimental and dlscussion in journal articles and the piecing together of the parts to form a lucid and usable whole . . . . . . A method is considered to be amprocedure in which a basic reaction, a special reagent, or a physical operation is used for the first time for the particular purpose and a modification as a method that has been distinctly improved in accuracy or convenience without a change in the fundamental features . . . . . . . In the triple designation of a method, first the originator is given, second the distinctive reagent, or reaction product, and third the class to which the method belongs. as the analysis of foods. In fact, the most di5cult-in
The scrupulous care of the authors to give full credit to the originators of methods is especially to be commended at a time when attention to such matters of etiquette is all too often neglected. The book is provided with an excellent 52-page index. The cuts of apparatus, graphs, and microscopic sections are well executed. Only a few typographical slips were noted, such as a misplaced decimal point, or a wrong algebraic sign-errors such as inevitably creep into a complex formula or escape the tired eye in the reading of proof. Dr. and Mrs. Winton are to be congratulated upon adding so worthy a volume to their list of publications on the chemistry, composition, and microscopy of foods. i.A. BROWSE
