March 15, 1935
ANALYTICAL EDITION
W. C. Rose of the University of Illinois, and C. H. Bailey of the University of Minnesota for their helpful suggestions in pursuing this work. The authors wish to thank W. Ndte of the American Dry Milk Institute, Inc., for his help in this manuscript, and especially to preciation to E*Copeland of this laboratory for his painstaking analytical work and whole-hearted cooperation.
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LITERATURE CITED (1) Assoc. Official Agr. Chem., Official and Tentative Methods, 1930. (2) Coe, M.R.,J.Assoc. OfficialAgr. Chem., 11,251 (1928). (3) Davis, A. B., Ibid., 11,410 (1928). RECEIVED July 3, 1934. Presented before the Division of Agricultural and Food Chemistry at the 88th Meeting of the Ameriaan Chemical Pociety, Cleveland, Ohio, September 10 to 14, 1934.
Determination of Copper in Organic Matter A Note on Ansbacher's Method OLIVESHEETS,ROBERTW. PEARSON, AND MARVIN GIEGER Mississippi Experiment Station, State College, Miss. Instead of placing the crucible containing the copper sulfide in N ACCURATE method for the determination of small glass triangle over a crystallizing dish, it is placed in a 50-cc. amounts of copper is of great importance to investi- aErlenmeyer flask, the top of which has been cut off so that the gators in the field of nutritional anemia, and is essential crucible will fit into it to a depth of about 1.25 om. (0.5 inch). A to the correct interpretation of results obtained from investi- lip is also made in one side of the flask for pouring and rinsing out gations on the role of copper in hemoglobin regeneration. the copper nitrate and sulfate solution. The use of the Erlenmeyer flask decreases the danger from copper contamination, and Unreliable methods for the determination of copper are loss of the sample due to the crucible tipping over. doubtless partially responsible for the conflicting opinions To dissolve the cop er sulfide and evaporate the copper nitrate which exist in this field of research. and sulfate solution t i e Erlenmeyer flask is placed on an alumiFor several years the Department of Home Economics has num water bath which rests on an electric hot plate having aluminum top and sides. The hot plate is placed in a metal-free been trying out copper methods in an attempt to find one hood lined with asbestos sheet rock. Evaporation to dryness can which would prove satisfactory in the analysis of food materials. usually be completed on the water bath, but it may be necessary Modifications of the xanthate (IO), the Biazzo (7), and the car- to place the flask directly on the hot plate for a few minutes. bamate method as described by Callan and Henderson (3) It is also desirable, as Ansbacher suggests, t o have a glass plate were all tried out, but the results obtained were not reliable. over the crucible and flask to exclude copper contamination. INTERFERING ELEMENTS. The authors have encountered (A recent modification of the carbamate method has been reported, 8, which the authors have not tried.) The only no difficulty with interfering elements in the foods analyzed. method which has thus far given consistent results is one in Ansbacher found that other metals which might occur in which chromotropic acid is used. This method was de- biological materials, including those of the second group, did veloped by Ansbacher (a),but has not as yet been adopted by not interfere with the method (5). However, if an excess of sulfur is present the final solution is many investigators in the United States. It is applicable to a wide variety of biological materials. The authors have used acid instead of neutral. When fuming nitric acid is used in it successfully for the analyses of vegetables and sirups, and wet ashing, a part of it may remain after digestion, and when Ansbacher and collaborators for the analyses of fruits, vege- hydrogen sulfide is passed through the solution considerable tables, milk, eggs, oysters, meat, and other animal products free sulfur is precipitated. This forms sulfuric acid in the (1, 2, 4). The chief difficulty in the use of this method is the subsequent treatment with fuming nitric acid, producing an determination of the end point when titrating with the acid residue on evaporation. When an unknown quantity of chromotropic reagent. The authors have been able to over- acid remains in the final solution, it is impossible to determine come this difficulty, and in addition have developed certain the quantity of ammonia to add without the use of an indicator. If the solution is too acid or too alkaline, low results details of technic which it seemed worth while to report. are obtained. Sulfuric and perchloric acids alone are, thereMETHOD fore, used in wet ashing, although nitric acid may also be used if care is taken to remove all of it after the digestion is comI~ESTRUCTIONO F ORGANIC MATTER. If the material to be analyzed contains sufficient copper so that a small sample (1to pleted. This may be done by cooling the digest, adding 3 5 grams) may be used, it can be wet ashed. If a larger sample volumes of water, and concentrating by rapid boiling. PREPARATION OF CHROMOTROPIC REAGENT.The sodium is required, dry ashing is preferable. With certain materials which are difficult to ash, such as sirups, a combination of wet salt of the nitroso-chromotropic acid is made by dissolving 0.35 gram of chromotropic acid (Eastman Kodak Co. No. and dry ashing was found to be most satisfactory. 1613) in 5 cc. of water and adding 0.21 gram of sodium carbonFor this method the weighed sample is placed in a silica or platinum dish and ashed in an electric muffle. The initial ate, 0.5 cc. of 2 N sodium nitrite, and a slight excess of dilute temperature should be below 100" C. The heat is rapidly acetic acid. Otherwise, the method described by Ansbacher increased until the temperature reaches 450' C. If a stream of for making up and standardizing the chromotropic reagent is air is drawn through the furnace, less time is required for ashing followed. and a more complete ash is obtained. The time re uired is about DETERMINATION OF COPPER. When titrating with the 2.5 hours, varying with the nature of the materij The ash is washed into a 300-cc. Kjeldahl flask with copperlfree distilled chromotropic reagent, a colorimeter was first used to deterwater; the dish is washed with 10 cc. of concentrated sulfuric mine the end point, since the change in color from a purple to a acid, which is added to the ash. The latter is digested for 10 brown tinge could be detected by this means when it could not minutes, adding 1 cc. of 60 per cent perchloric acid if necessary to be detected by the naked eye. When the eye becomes clear the solution, and transferred to a 300-cc. Erlenmeyer flask. trained to observe the slight color change, it is not necessary PRECIPITATION OF COPPERAND SOLUTION OF COPPER to use the colorimeter. In standardizing the chromotropic reagent as well as in the SULFIDE.The procedure is the same as that described by determination of copper in the unknown, the authors use a Snsbacher with the following modifications:
I N D U S T R IA L A N D E N GIN E ER IN G C H E M I ST R Y
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series of four or more test tubes containing the same aliquot of standard or unknown. To obtain the best results, a 5-cc. aliquot should contain from 3 to 157 ( l y = 0.001 mg.) of copper. Too dilute or too concentrated solutions give colors which make it difficult to determine the end point. A preliminary titration will show the approximate amount of copper in the unknown after the titer has been determined for the chromotropic reagent, which is added to the aliquots in gradations of 0.1 cc. At one end of the series the color in the test tubes should he distinctly purple, a t the other end distinctly brown. The first aliquot which shows a brown tinge when examined in the colorimeter is taken as the end point. TABLE r. RECOVERY OF ADDEDCOPPER SAMPLE
COPPERIN SAMPLE P.p.m.
13 (sirup) 9 (sirup) 307 peas) 308 [pea@) 309 (peas) 310 (peas) 104 (sirup) 105 (sirup)
4.38 8.34 73.30 73.00 71.50 81.20 2.90 3.50
COPPER
ADDED P.p.m. 1.27 1.27 2.30 4.60 11.60 23.00 37.70 50.90
NOTE. After this manuscript was submitted for publication, two papers of interest with regard to copper methods were published (6, 9). Conn and collaborators (6) make the following statement with regard to the four copper methods which they employed: “Summarizing experience with these four methods, the chromotropic acid method can be eliminated because of the difficulty in distinguishing the end point. The Biazzo method is not sufficiently sensitive. The possibility of interference due to turbidity makes the xanthate method undesirable. The carbamate method appears to be by far the most desirable, since it is the most sensitive, and the disturbing factor of turbidity is not encountered.” The 4, 6) and Ohlauthors’ results as well as those of Ansbacher (l,,??, son (9) have demonstrated that the chromotropic acid method is at least as sensitive as the carbamate method of Conn and collaborators, and apparently more reliable, judging by a comparison of the data on recovery of added copper for the two methods.
TOTAL ADDED COPPER COPPER COPPER FOUNDRECOVERED RECOVERED P.p.m. P.8.m. lol %,6 5.67 1.29 9.66 1.32 103.9 75.40 2.10 91.3 78.00 5.00 108.7 82.60 11.00 ”’’ 104.50 23.30 101.3 42.90 40.00 106.1 54.10 50.60 99.4
The authors were unable to distinguish differences in color where less than a drop of the chromotro~icreagent was used, If the reagent was to ‘”7 Of copper per One drop or 0.05 cc. would be equivalent to 0 . 3 3 5 ~of copper. Ansbacher found the reagent to be accurate to 0 . 5 of ~ copper. Table 1 shows the recovery of copper added to sorghum sirup and peas. ”*,
VOl. 7, No. 2
LITERATURE CITED
(1) Ansbaoher, “&tude de Chimiothbrapie de la Tuberculose,” pp. 26-35, Geneva, Imprimerie Kundig, 1933. (2) Ansbacher, Remington, and Culp, IND.ENG.CHEM.,Anal. Ed., 3,314 (1931). (3) Callan and Henderson, Analyst, 54,650 (1929). (4) Cherbuliez and Ansbacher, Arch. path. Anat. (Virchow’s),276, 365 (1930). (5) Cherbuliei and Ansbacher, H e h . Chirn. Acta, 13, 187 (1930). (6) Conn, L. W.,Johnson, A. H., Trebler, H. A., and Karpenko, V., IND.ENG.CHEM.,Anal. Ed., 7, 15 (1935). (7) Elvehjem and Lindow, J. Bioi. Chern., 435 (1929). ( 8 ) Moseley, H. W., Rohwer, A. G., and Moore, M. C., Science, 79, 507-8 (1934). (9) Ohlson and Daum, J. Nutrition, 9, 76 (1935). (10) SuPPlee and Bellis, J. Dairy SCi.9 5,455(1922). RECEIVDD December 10,1934.
Adsorption of Organic Liquids by Cellulose Products J. WIERTELAKAND I. GARBACZ~WNA, Institute of General Chemistry, University of Poznan, Poland
A
TTENTION has recently been called by Mease (6) to the fact that other liquids than water may be held tenaciously by fibrous materials. The same conclusion has been arrived a t independently by Booth (1) and Wiertelak (8) in connection with standard analyses performed on cellulose and wood products. In case the samples analyzed contained but minute a’mounts of extractives, they were found to weigh more after extraction with an organic solvent, such as a benzene-alcohol mixture, and subsequent drying to constant weight than before the extraction, although the solvent undoubtedly contained some extracted substances. This study was therefore undertaken in order to extend the scant information offered by Mease as well as to ascertain to what extent the adsorption of organic liquids may interfere with standard analyses of wood and cellulose products, as they are usually performed in technical laboratories.
EXPERIMENTAL *
Adsorption experiments have been performed on the following cellulosic substances: commercial adsorbent cotton; Cross and Bevan cellulose prepared from white birch, probably Betula papyrijera, Marshall; commercial viscose rayon and commercial nitrate rayon, both supplied by the Rayon Works a t Tomasz6w, Poland; and commercial cuprammonium rayon, supplied by the Bemberg Aktien Gesellschaft a t Barmen, Germany. The chemical composition of these
cellulose products is described in detail in a recent paper by Wiertelak (8). The liquids used for adsorption were: commercial 95 per cent ethyl alcohol; methyl alcohol Kahlbaum; n-butyl alcohol Kahlbaum, gereinigt; n-propyl alcohol, Merck; commercial diethyl ether; benzene, Merck or Kahlbaum, purum; commercial gasoline, boiling range 100’ to 150’ C.; pyridine, Polish Coke Association, purissimum; a benzenealcohol mixture, 1 to 2; and a benzene-alcohol mixture, 2 to 1. The two benzene-alcohol mixtures were prepared from commercial 95 per cent ethyl alcohol and Merck or Kahlbaum benzene. All liquids were redistilled repeatedly before use. Most of the above cellulose specimens were used in air-dry condition, their moisture content being shown by a separate determination to amount to from 7 to 10 per cent on the basis of the oven-dry sample. Approximately 1 gram of the airdry sample, accurately weighed, was placed in an Erlenmeyer flask and kept in a thermostat a t 25’ C.for 15 minutes in contact with 25 cc. of the liquid to be tested. Then it was filtered through an alundum crucible, dried in air in an electrical drying oven a t 105’ C. to constant weight, and weighed. In one series a sample of cotton was oven-dried a t first, and then treated with the adsorption liquid. The rest of the procedure was the same as above. The percentage increase in the oven-dry weight due to adsorption, calculated on the basis of the oven-dry weight of the fibers before treat-
