ANALYTICAL EDITION
March 15, 1941
Add 30 cc. of the brucine sulfate solution followed immediately by 30 cc. of the potassium iodide solution. Stir well and let settle for 10 minutes. Filter through a 5-cm. (2-inch) Buchner
funnel, using moderate suction and a very fine paper. Wash the beaker with a 50-50 mixture of the stock solutions (mixed immediately before use) three times and the paper three times with a-1 to 4 mixture of ethanol and toluene. ESTIMATION.Wash the precipitate and paper back into the beaker with water, making up to 100 cc. Heat until the precipitate has dissolved. Add 5 cc. of a 0.5 per cent solution of eosin Y 9s an indicator and titrate to the absorption end point with 0.03 N silver nitrate (6). The titration value is compared to that of a standard test to give the amount of cadmium in the sample.
Notes I n making u p the brucine sulfate solution, the addition of sulfuric acid u p to 5 per cent is helpful in the solution of the brucine and in the adjustment of the acidity during the precipitation. Care must be taken, however, not to oxidize the brucine. For best results, a fresh solution of brucine sulfate should be made every day. Excessive volume for the precipitation may cause a colloidal precipitate. Difficult filtrations may be aided b y judicious choice of filter papers and filter aids. If there is a large mass of precipitate, it may hold some of the iodide solution, raising the titer and affecting the factor. It may be necessary to dissolve and reprecipitate the cadmium. The work requires only a few minutes and may be well worth the time.
165
As in most analytical procedures, directions must be minutely followed, and a definite technique established. Careless work or minor differences in procedure may vitiate all results. Short cuts or the removal of additional elements will doubtless cause a different titer value. Careful work and a n established technique, always qualities of a good analyst, are fully repaid b y extremely accurate and rapid determinations of cadmium that will effect savings in time and money, especially in the large routine laboratories of smelters and metal-working plants.
Acknowledgment Acknowledgment should be made of the valuable assistance of L. H. Haslip of the American Zinc Company of Illinois for his advice in formulating routine laboratory procedures and of the cooperation of the American Zinc Company for the use of its laboratory in which a portion of the work was done.
Literature Cited (1) Banner, J., 2.anal. C h m . , 75,321-71 (1928). (2) Goto, H., Science Repts. TBhoku Imp. Univ., First Ser., 26, 391413 (1937). (3) Korenman, I. M., Zavodskaya Lab., 6, 1461 (1937). (4) Mahr, C.,Mikrochem. Acta. 3, 300-3 (1938). (5) Reese, J. T., Bur. Mines, Bull. 22, 71-84 (1937). (6) Scott, “Standard Methods of Chemical Analysis”, New York, D. Van Nostrand Co., 1929. (7) Treadwell and Hall, “Analytical Chemistry”, 8th ed., Vol. 11, p. 198, New York, John Wiley & Sons, 1939.
Detection of Sodium Alginate in Dairy Products CHARLES W. SCHROEDER AND PHILEAS A. RACICOT Massachusetts Department of Public Health, Boston, Mass.
A
MONG the thickening agents being used a t the present
time in the dairy industry is the sodium salt of alginic acid, derived from certain seaweeds and put on the market in various forms. The product which is probably most widely used in this country is sold under the trade name of Dariloid, in which sodium alginate is mixed with other substances including dextrin, sucrose, and a phosphate. Other commercial products may consist of the pure alginate. The present investigation was undertaken because of a lack of a specific qualitative test for alginic acid. The test is needed because of the widespread use of alginates in several dairy products, especially ice cream; and because of the possibility of illegal use in milk, cream, or other dairy products. Inasmuah as the commercial product is likely to contain dextrin, a quick preliminary test for dextrin may be used to establish the probable presence of alginic acid in milk or cream. Likewise, milk or cream containing the commercial product is likely to give a positive Rothenfusser test (1) for sucrose.
Tests OPTIONAL PRELIMINARY TESTFOR DEXTRIN. Take 10 cc. of milk or cream, dilute with 10 cc. of distilled water, and add 10 cc. of a 20 per cent solution of trichloroacetic acid. Shake vigorously for 1 minute, let stand for 5 minutes, and a t e r . Make the filtrate alkaline with ammonium hydroxide, evaporate on a steam bath to a volume of about 1 cc., a t e r into a test tube, cool to room temperature, and add 0.05 N iodine solution cautiously to the atrate, a small drop a t a time. A violet to reddish-violet color indicates the possible presence of 0.1 per cent or more of Dariloid. SPECIFICTESTFOR ALGINICACID. To 20 grams of milk, cheese, cream, or ice cream add a volume of concentrated hydro-
chloric acid approximately equal to the water content of the sample taken. Shake thoroughly, add a little sand (acid-washed and ignited), bring to a boil, and boil 30 seconds with frequent shaking. Transfer to a 50-cc. centrifuge tube with the aid of 10 to 20 cc. of alcohol. Centrifuge 10 minutes, or until the solid matter forms a compact cake a t the bottom of the tube, and decant as much of the supernatant liquid as possible from the solid matter, taking care not to lose any of the solids. The centrifuge should be warm enough to keep the fat liquid and should be allowed to slow down without braking, to avoid stirring u the solids. I n some cases, the fat mixed with part of the solids at the surface a dense cake which must be punctured with a stirring rod to allow removal of the liquid. The decantation is best carried out against a white background to facilitate observation of the solids through the dark solution. Wash the solids repeatedly with 75 per cent ethyl alcohol by shaking, centrifuging, and decanting as above, until the wash solution is neutral to litmus paper and is colorless. Then wash twice with ether in the same manner. Evaporate the last traces of ether by warming the tube in a beaker of hot water and directing a current of air into it. Dissolve the residue so far as possible in 10 cc. of 0.1 N sodium hydroxide by shaking a few seconds. Filter, wash the tube and paper with a few cubic centimeters of water, and to the filtrate add an equal volume of 95 per cent ethyl alcohol. Centrifuge 10 minutes, decant the supernatant liquid, and wash the solids with 75 per cent alcohol by centrifuging and decantation until the wash solution is neutral to litmus paper. The solution should be centrifuged and decanted even when it appears clear, as small amounts of gum are invisible beforehand. If the separated gum is now white and free from any yellow or brown color, pass over the next paragraph. Suspend the gum in 10 cc. of distilled water and add 0.1 N sodium hydroxide dropwise, with shaking, until the solution is just alkaline to litmus paper. Add 6 cc. saturated magnesium nitrate solution and shake thoroughly. Centrifuge 10 minutea and decant the supernatant liquid from any precipitate into another centrifuge tube. Discard the precipitate and make the solution acid with a drop of concentrated hydrochloric acid.
perms
166
INDUSTRIAL AND ENGINEERING CHEMISTRY
Centrifuge, decant, and wash the precipitate with 75 per cent alcohol as before, until neutral. Dry the gum by warming the tube with hot water and blowing air into it until no odor of alcohol is perceptible. Dissolve as far as possible by shaking with 0.15 cc. of 0.1 N sodium hydroxide, add 1 cc. of sulfuric acid reagent, shake thoroughly, and let stand a t room temperature. [The sulfuric acid reagent vias prepared by precipitating ferric hydroxide from ferric chloride solution with ammonium hydroxide, washing the ferric hydroxide until neutral, drying on the steam bath, and finally saturating concentrated sulfuric acid with the dry ferric oxide by allowing the two to stand in contact for several days. The clear acid solution was then decanted from any excess ferric sulfate.] Within a few minutes to several hours, depending on the amount of alginic acid present, the solution will develop a pink color deepening through cherry red to magenta, and finally becoming a deep purple. When the amount of gum is 0.5 mg. or less, the purple color is permanent for a t least 1 week, but with larger amounts the color eventually changes to a brown-black. Table I shows the time required for development of the color with various amounts of the gum.
Discussion By means of this test, i t is easily possible to detect 0.2 per cent of sodium alginate or Dariloid in dairy products. The following substances do not interfere with the test: starch, gelatin, Irish moss, agar, gum tragacanth, India gum, locust bean gum, gum arabic, and formaldehyde. The test
Vol. 13, No. 3
has been found satisfactory with a 0.2 per cent solution of Dariloid in milk, heavy cream, cream cheese, and vanilla, strawberry, chocolate, and maple walnut ice cream. TABLEI. DEVELOPMENT OF COLOR Time for Development of Violet Tinge
Time for Development of Deep Purple Color
0.04 0.1
No color developed Overnight
0.3 0.5 1.0 3.3
4 hours
No color developed Not reached after standing one week Overnight Overnight 3 hours 1 hour
Weight of Dry Gum
Mw.
4 hours 10 minutes 2 minutes
In order to make sure that the substance which gives the color test with the sulfuric acid reagent was derived from the sodium alginate and not from any accompanying impurity, a sample of sodium alginate, which was represented as being substantially pure, was obtained from the Kelco Company. This product was dissolved in water and precipitated by the addition of an equal volume of concentrated hydrochloric acid. The mixture was then boiled for 1 minute and the residue washed free of acid by repeated centrifugalization and decantation. The residue was then dissolved in just sufficient 0.1 N sodium hydroxide and the whole process repeated five more times. The residue from the final acid precipitation was assumed to be free of any contaminants and still gave the color test.
Literature Cited (1) Rothenfusser, 2. Nahrungs. Genussmittel, 19, 465 (1910). PRESENTED before the Division of Agricultural and Food Chemistry at the 100th Meeting of the American Chemical Society, Detroit, Mich.
Determination of Menthol in Oil of Peppermint THOMAS W. BRIGNALL, A. M. Todd Company, Kalamazoo, Mich.
E
ACH year i t is necessary for the author’s laboratory to
analyze several hundred samples of oil of peppermint within the short period which comprises the harvesting season. It has, therefore, been the constant aim to devise a method which would permit more rapid analyses without sacrificing accuracy. The method of Power and Kleber (6), which is generally used in the aromatics industry and is the official procedure of the United States Pharmacopoeia, is known to be erroneous and to give variable results in different laboratories; however, none of the modifications proposed thus far has been entirely satisfactory. This procedure is known to indicate as alcohols such nonalcohol constituents as aldehydes, amines, phenols, esters, and some of the more unstable terpenes which are acetylated along with the alcohols when that method is used. The present are included during saponification. During the course of research this method has been thoroughly investigated and, as a basis for further conclusions, i t is believed advisable to review briefly the possible sources of error in the order in which they occur during the analysis of an oil. These discrepancies include those observed in the author’s laboratory as well as those reported in the literature. In a report upon the analysis of oil of peppermint, Nelson (5) states that “the proper care of the sample previous to analysis is highly important: all reagents used must be of the best quality and the so$um acetate used as a catalyst must be absolutely anhydrous. It has been observed here that acetic anhydride must be used within a short time after the container is opened; otherwise, deterioration of the anhydride, due to its hygroscopic nature,
will be evidenced by low results in alcohol analyses. Frequent standardization of solutions, especially of the alcoholic potassium hydroxide, is necessary to ensure consistent results. It has been found necessary to use hot solutions when washing the acetylated oil to hydrolyze the excess acetic anhydride completely. No evidence of hydrolysis of the acetylated oil has been found if this procedure is used and the dried acetylated oil has always been neutral. The author has long stressed an exact 1-hour saponification time, having observed that variations in this factor caused marked differences in results. Recently Baldinger ( 1 ) conducted a time study, varying the length of both acetylation time and saponification time with each sample. The interpretation of the results of this study is summarized as follows: “It would seem that the time of acetylation may vary within broad limits, while the time of saponification had best be varied between 45 and 60 minutes. While experimental evidence is not yet available to prove the contention, it is believed that resinification or polymerization of certain constituents is induced by prolonged heating with potassium hydroxide aycl that some base is used up, thereby leading to erroneous results. Redemann and Lucas ( 7 ) have observed that more rapid hydrolysis of esters results if diethylene glycol is substituted for ethyl alcohol as a solvent for potassium hydroxide. This has been verified by Hall, Holcomb, and Griffin ( 4 ) ,who applied this method to the analysis of the isomers of menthol. In the titration of the saponified oil, variations occur due to differences in the estimation of the end point by different analysts. Badly oxidized or poor quality samples are often difficult to analyze consistently, owing t o discoloration during saponification. This interferes with the observation of the end point when phenolphthalein is used as an indicator. The method of Delaby, Sabetay, and Breugnot ( 2 ) for the determination of free alcohols in the sandalwood oils gives results from 5 to 8.5 per cent lower than those obtained by Power and Kleber. These authors traced this divergence to the fact that
