DECEMBER 15, 1939
ANALYTICAL EDITION
Gossett, W. S., Biometrika, 6, 1 (1908). Goulden, C. H., “Methods of Statistical Analysis”, Chap. IV, New York, John Wiley & Sons, 1939. Ibid., Chap. IX. Ibid., Chap. XI. “Handbook of Chemistry and Physics”, Cleveland, Ohio, Chemical Rubber Co., Mathematical Tables. Also any book on statistics. Haynes, Dorothy, and Judd, H. M., Biochem. J., 13,272 (1919). Holmes, M. C., “Outline of Probability and Its Uses”, p. 28, Ann Arbor, Mich., Edwards Bros., 1936. Ibid., p, 48. Hooker, S. C., J . Am. Chem. Soc., 58, 1165-7, 1178 (1936). Ingram, G., J . Soc. Chem. Ind., 58, 34 (1939). Lundell, G. E. F., IKD.ENG.CHEM.,Anal. Ed., 5, 221 (1933). Munch, J. C., J . Am. Pharm. Assoc., 37,404 (1938). Neyman, J., “Lectures and Conferences on Mathematical Statistics”, p. 45, Washington, D. C., Graduate School, U. S. Dept. of Agriculture, 1938. Niederl, J. B., and Niederl, Victor, “Micro Methods of Quantitative Organic Analysis”, p. 109, New York, John Wiley & Sons, 1938. Ostwald, Wilhelm, and Luther, Robert, “Hand- und Hilfsbuch zur Ausfuhrung physico-chemische Messungen”, 5th ed., p. 13, Leipzig, Akademische Verlagsgesellschaft, 1931. Pearson, E. S., “Application of Statistical Methods to Industrial Standardization and Quality Control”, Section 8, Table 13, London, British Standards Institute, 1935. Power, F. W., “Probable Error of Microdetermination of Carbon and Hydrogen”, presented before Microchemical Section, American Chemical Society, Chapel Hill meeting, April, 1937.
673
Power, F. VI., “Some Temperature Effects in Microchemical Weighing”, presented at Milwaukee meeting, American Chemical Society, September, 1938. (33) Pregl, Fritz, andRoth, H.,“Quantitative Organic Microanalysis”, 3rd English ed., tr. by E. B. Daw, p. 13, Philadelphia, P. Blakiston’s Son & Co., 1937 (34) Reinitser, F., Monatsh., 9, 421 (1888). (35) Rider, P. R., “Introduction to Modern Statistical Methods”, Chap. VI, New York, John Wiley & Sons, 1939. Ibid.., Chaa. - ~ VII. Ibid., Chap. VIII. Schwarz-Bergkampf, Erich, 2. anal. Chem., 69, 321 (1936). Scott, E. L., J . Biol. Chem., 73,81 (1927). Shewhart, W. A,, “Economic Control of Manufactured Product”, p. 95, New York, D. Van Nostrand Co., 1931. Ibid., p. 184. Ibid., p. 277. Ibid., p. 390. Shewhart, W. A., “The Statistical Method from the Viewpoint of Quality Control”, issued for Dept. of Inspection Engineering, Bell Telephone Laboratories, Inc., New York (1937); to be published by Graduate School, U. S. Dept. of Agriculture, Washington, D. C. Ibid., p. 30. Snedecor, G. W., “Calculation and Interpretation of Analysis of Variance and Co-variance”, pp. 13 ff., Ames, Iowa, Collegiate Press, 1934. Wieland, H., Ann., 507, 226 (1933). Wieland, H., and Kotzschmar, A., Ibid., 530, 152 (1937). Williams, R. J., IKD. EKG.CHEM.,Anal. Ed., 8, 229 (1936). ~
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Volumetric Estimation of Lac on Glazed Candies NICHOLAS Bl. MOLNAR AND JOSEPH GRUMER Molnar Laboratories, New York. N. Y.
T
HE widespread use of lac for coating candies and the
establishment by the new Food, Drug, and Cosmetic Act of a maximum permissible lac content have stimulated interest in the development of a method for the estimation of semimicroquantities of the material. The method presented here, based on the extraction and the titration of the lac acids with standard sodium carbonate, is quick and simple enough to be used in control testing in the manufacture of glazed candies.
Requirements of the Food, Drug, and Cosmetic Act The production of arsenic- and lead-free lac enabled candy manufacturers to use lac coating on candies to serve a double purpose: (1) to form a protective seal, and (2) to produce a desirable glaze. The Food, Drug, and Cosmetic Act (2) allows the use of such harmless glaze, but not in excess of 0.4 per cent. A manufacturer of candies, well before the law went into effect, asked the authors to render analysis on the lac content of his candies, in order to modify his manufacturing procedure if necessary and to ascertain that his products are within the law. A search of the literature showed no methods for the estimation of lac on glazed candy, but various articles (1, 3, 7, 8, 11) dealing with the chemical composition of shellac, none of which could be used for quantitative estimation in a complex system such as candy. The United States Department of Agriculture, Food and Drug Administration, advised (9) that they had had little or no occasion to determine glaze on candy quantitatively; hence they have no immediately available method for quantitative analysis of glazed
candy for shellac content. The need for a quick and accurate method is obvious. In manufacturing, a quick control with results obtainable within a few hours is essential, so that before the candies are packed the manufacturer may be certain that his product is within the requirements of the law.
Discussion I n the manufacture of glazed candies the glaze is applied by means of a solution of pure lac in specially denatured alcohol 35, an authorized formula (10) for a solvent in manufacturing candy glazes under code 015. This formula is prepared by the addition of 35 gallons (9.25 liters) of ethyl acetate to 100 gallons (26.4 liters) of pure ethyl alcohol. Tests run on samples of refined lac such as is used in the candy industries showed that alcohols 35, 2B, and 3A were satisfactory solvents. Alcohol 2B is made by adding 0.5 gallon of benzene to 100 gallons of ethyl alcohol, and alcohol 3A by adding 5 gallons of commercially pure methyl alcohol to 100 gallons of ethyl alcohol. (Though the use of alcohols 2B and 3A is permissible in analysis, they are not to be recommended for use as solvents for lac used for glazing candies.) Inasmuch as other constituents of many candies-namely, dextrose, coloring matter, fatty matter, and alkaloids such as theobromine-would be extracted in part or completely, evaporation of the alcoholic extract and subsequent weighing could not be used. Water could be added to precipitate the lac from the alcoholic solution, but the partial formation of colloidal dispersion as well as the precipitation of fats made the method of filtration and weighing impractical. It was then decided to base the determination on the solvent proper-
INDUSTRIAL AND ENGINEERING CHEMISTRY
674
ties of alkali on the lac acid (11). Sodium carbonate was chosen because it can be used as a primary standard, thus avoiding the need of standardizing its solution. The reaction is (9)
H shellacate
+ NaaCOs +NaHCOs + Na shellacate
The literature was again consulted to determine the equivalent value of lac in terms of sodium carbonate. Rogers gave 8 as the equivalent (4), while Murty of the Indian Lac Research Institute gave 7.7 (9). To facilitate calculation and titration, a standard solution of sodium carbonate containing 1 mg. per cc. was prepared. Titrations were run on aliquot portions of a weighed sample of pure lac in alcohol 2B. This alcohol and 3A were preferred to alcohol 35 because the denaturant of alcohol 35 reacted slowly with alkali, interfering with the sharpness of the end point. Phenolphthalein was first used as indicator, but the light purple-red color due to formation of lac dye from chromogen, which is not entirely removed in lac processing, confused the end point (5). Phenol red, which gives a strong red color a t a slightly lower pH than phenolphthalein, was found to be a satisfactory indicator. The end point occurs a t the point where only sodium shellacate and sodium bicarbonate are in the solution. The first drop of excess sodium carbonate should signify the end point, at the transition pH where phenolphthalein turns red. The color obtained in the titrated solution by adding one drop in excess is too weak to be readily distinguished from the light purple-red produced by the lac dye formation. Titrations on aliquot portions of alcoholic lac solutions, run by the method outlined below, agreed most closely with the factor 8 as being the lac equivalent of one part of sodium carbonate. This is in agreement with Rogers (4) and in close agreement with Murty (9). The factor as well as the method was further checked by determining the lac content of aliquot samples of glazed candies, Known quantities of lac were added and the total lac content was determined. The difference checked closely with the added charge of lac. Light orange refined lac, such as is used in the candy industry, was used in these tests because of its permanence in this climate. Bleached lac offers a difficulty in its gradual change into an alcohol- and alkaliinsoluble form (6). This change cannot be stopped and will take place in time with every bleached lac (6). For this reason candies treated with solutions of bleached lac should be tested promptly. TABLEI. RECOVERY OF KNOWN QUANTITIES OF LAC Charge MU. 49.7 50.0 63.3 58.6 30.8 38.2 37.1 37.0
Recovered, Using Factor 8
-Error-
10 grams of candy
20 grams
%
%
Mg. 49.1 49.2
of candy
64.0 58.0 34.2 38.4 37.0 30.4 I
Method Fifty grams of candy, glazed with pure lac, are weighed on a quantitative balance, or, since only four significant figures are needed, on a good platform. The candy is covered with alcohol 3A or 2B and allowed to stand with occasional stirring for 1hour. Generally less than 40 cc. of alcohol are needed. The alcohol is decanted through filter paper into a 50-cc. volumetric flask or into a 100-cc. flask if necessary, 10 cc. more of alcohol are added t o the candy, allowed to stand with occasional shaking for 0.5 hour, and decanted through the same filter paper into the same volumetric flask. The candy is washed with sufficient alcohol t o bring the alcoholic extract up t o volume. Twenty cubic centimeters of filtrate are transferred t o a 125cc. flask or beaker. If the lac solution has been brought up to
VOL. 11, NO. 12
50 cc., the charge taken for titration represents approximately 20 grams of candy; if it has been brought up t o 100 cc. the charge is approximately 10 grams. Twenty cubic centimeters of distilled water are added with shaking. The dispersion is brought up to boiling and kept at the boiling point for at least 5 minutes and 3 to 5 drops of henol red are added. The lac is titrated while hot with s t a n i r d sodium carbonate till a deep red is obtained which matches the color formed by adding 1 to 2 drops of the standard solution t o a similarly treated 50 per cent alcohol solution which has been kept at the boiling point for at least 5 minutes. Boiling for at least 5 minutes serves two purposes: Sodium carbonate will not dissolve lac in the cold, and it is necessary to boil out carbon dioxide, since it will effect the titration. The number of cubic centimeters of alkali consumed, multiplied by 8, is equal to the number of milligrams of lac in the titrated sample.
TABLE 11. RECOVERY OF KNOWN ADDITIONS OF LACTO GLAZED CANDY Charge Added Mg.
Predetermined Lao Content of Candy %
Reoovery of
Added Lac Me.
C -
10 grams of candy
%
Error--
20 grams of oandy
%
Preparation of Solutions Standard Sodium Carbonate. One gram of anhydrous c. P. sodium carbonate is dissolved in 1 liter of freshly boiled distilled water. Phenol Red. In a mortar 0.1 gram of dry phenol red is mixed with 28.2 cc. of 0.01 N sodium hydroxide, and diluted to 250 cc. with distilled water.
Possible Interferences Organic acids, particularly citric acid, are present in some candies. When their presence is suspected or in the event of a very high lac figure, it is advisable to titrate a water extract of the candy and deduct the number of cubic centimeters of sodium hydroxide consumed from that needed in the lac titration, Fatty acids can be accounted for by first extracting the acids from the candy with carbon tetrachloride. After evaporation of the solvent the fatty acids can be redissolved in alcohol and after the addition of water, titrated with the standard sodium carbonate, remembering that 6.8 per cent of the lac is soluble in carbon tetrachloride (8). The fatty acid-free candy can then be analyzed for remaining lac content. I n the course of this work, over 250 samples of candy were tested for lac content. I n only two instances was i t necessary to provide for interferences-namely, citric acid. Though in no case did the authors know the true lac percentage, they feel that the results of analyses run on known quantities of lac and on candies before and after the addition of known quantities of lac have proved the worth of this method.
Literature Cited (1) Barnes, IND.ENQ.CHEM.,30, 449 (1938). (2) Federal Food, Drug, and Cosmetic Act, 75th Congress, 8-5, Section 402d. (3) Murty, IND. ENQ.CHEM.,31, 239 (1939). (4) Rogers, A., “Manual of Industrial Chemistry”, 5th ed., p. 1103, New York. D. Van Nostrand Go., 1931. (5) Ibid., p. 1104. (6) I b i d , , p. 1105. (7) Schaeffer and Gardner, IND.ENQ.CHEM.,30, 333 (1938). (8) Schaeffer, Weinberger, and Gardner, Ibid., 30, 45 (1938). (9) U. S. Dept. Agriculture, Food and Drug Admin., personal communication, Oct. 25, 1938. (10) U. S. Treasury Dept., Bur. Int. Revenue, App. to Reg. 3, p. 24, Washington, D. C., Government Printing Office, 1939. (11) Weinberger and Gardner, IND.ENQ.CHEM.,30, 454 (1938).
