INDUSTRIAL AND ENGINEERING CHEMISTRY
July 15, 1931
Cajori, J . Biol. Chem., 64, 617 (1922). Chapin, J . A m . Chem. SOC.,38, 625 (1916). Colin and Lievin, Bull. SOC. chim., 23, 403 (1918). Englis and Byer, IND. END. CHEM.,Anal. Ed., 2, 121 (1930). Fiehe, Z. Nahr. Genussm., 52, 244 (1926). Goebel, J . Biol. Chem., 7 2 , 801 (1927). Gronover and Wohnlich, Z. Nahr. Genussm., 48, 405 (1924). Hinton and Macara, Analysl, 49, 2 (1924). Judd, Biochem. J . , 14, 265 (1920). Kline and Acree, IND. END. CHBM.,Anal. Ed., 2, 413 (1930); Bur. Standards J . Res., 6, No. 5 , 1060 (1930). Kolthoff, Pharm. WeekbZad, 60, 394 (1923); Z . Nahr. Genussm., 46, 141 (1923).
339
(19) Lane and Eynon, J . SOC.Chem. Ind., 42, 32T (1923). (20) Levy and Doisy, J . Bdol. Chem., 77, 733 (1928). (21) Mellor, “Comprehensive Treatise on Inorganic Chemistry,” Vol. p. 616, Longmans, Green, 1930. (22) Nyns, Bull. assocn. &ole sup. brasserie Louuain, 25, 63 (1925). (23) Romijn, Z. anal. Chem., 36, 18 (1897): 36, 349 (1897). (24) Schuette, J . A m . Oficial Agr. Chem., 11, 164 (1928). (25) Slater and Acree, IND. END. CHEM.,Anal. Ed., 2, 274 (1930). (26) Soxhlet, J . prakt. Chem., (2) 21, 227 (1880). (27) Voorhies and Alvarado, IND. ENG. CHEM, 19, 848 (1927). (28) Vosburg, J . A m . Chem. Soc., 42, 1696 (1920). (29) Willstatter and Schudel, Ber., 51, 780 (1918). (30) Zablinsky, Z . V n . deut. Zuckerind., 69 (N.S . 56), 159 (1919).
Impurities in White Sugars
x,
-
I I-De termination of Sulfates, Sulfites, and Aldehyde Sulfites112 J. A. Ambler, J.. B. Snider, and S. Byall BUREAU O F CHEMISTRY AND SOILS,WASHINGTON, D. C.
The quantity of sulfates in white sugars may be results shown in Table I, i t accurately determined by direct precipitation with present in the juices of is evident that sucrose does barium chloride from the acidified aqueous solutions the sugar cane (22) and not interfere in the precipitaof the sugars. By titration of acidified sugar solutions of the sugar beet (21) in tion of the barium sulfate and with standard iodine solution both before and after amounts varying annually that there is practically no treatment with alkali, the quantities of sulfur dioxide and also varying with the choice in the two methods. in the sugar as inorganic sulfites and as aldehydetype of soil and the climatic The cold method was adopted sulfite addition compounds may be determined. Some for the rest of the work on conditions. The quantity in sugars contain small quantities of other iodine-absorbcommercial sugars because of the factory juices is further ing impurities which it is suggested may be polyoften augmented by sulfates its simplicity and also because phenolic. in the lime (10, 28) and the it produced only very slight water (11) used in the manudiscoloration of th8 solutions, facturing processes, and in those factories which use sulfur whereas those which had been heated were badly discolored dioxide, by oxidation of sulfurous acid by the oxygen of the and turbid from the decomposition of the invert sugar formed air. Liming and carbonation do not completely remove the by the action of the acid on the sucrose. sulfates (19),a portion of which passes on into the evaporators Table I-Precipitation of Barium Sulfate in Presence of Sucrose and vacuum pans where the calcium sulfate frequently conSOa RECOVERED tributes to the formation of scale on the heating surfaces. SO3 TAKEN Hot precipitation Cold precipitation Gram Gram Gram The soluble alkali sulfates, unless their concentration is ex0.0049 0.0050 0.0056 tremely high, do not separate before graining of sugar and 0.0099 0.0096 0.0101 0.0493 0.0500 0.0502 are occluded in the growing sugar crystals. 0.0989 0.0986 0.0974
HE s u l f a t e i o n i s
T
Determination of Sulfates
The true quantity of sulfates in white sugar cannot be determined from an analysis of the ash of the sugar because during incineration at least a portion of the sulfates is reduced to sulfide by the carbon formed from the sugar, as is shown . by the stain of sulfide formed on the dish when the ashing is done in platinum, and by a distinct odor of hydrogen sulfide when the ash is acidified. However, the sulfates may be accurately and easily determined in acidified sugar solutions by precipitation with barium chloride (9). Two series of solutions containing known quantities of potassium sulfate in 200 grams of 50’ Brix solutions of cube sugar were prepared and acidified with 5 cc. of concentrated hydrochloric acid. One series was heated to boiling and treated with 10 cc. of 10 per cent barium chloride solution. The other series was treated a t room temperature with the same quantity of barium chloride. After the solutions had been thoroughly stirred, they were allowed to stand overnight, the first series on the steam bath, the other a t room temperature. The precipitated barium sulfate was collected on tared Gooch crucibles fitted with thick asbestos pads, washed thoroughly with hot water, dried, and heated to 550’ C. in a muffle furnace, cooled, and weighed. From the 1 2
Soils.
Received April 20, 1931. Contribution 109, Carbohydrate Division, Bureau of Chemistry and
0.1972
0.1965
0.1967
For the determination of sulfates in white sugars, 5 cc. of concentrated hydrochloric acid and 10 cc. of 10 per cent barium chloride solution were added to 100 grams of the sugar dissolved in 100 cc. of water. The mixtures were stirred thoroughly and allowed to stand overnight. After the precipitated barium sulfate had been collected and weighed as before, it was calculated to the equivalent weight of SOs. Some of the results on typical white sugars are recorded in Table 11,column 3. The second column gives the percentage of ash in the various sugars as determined by direct charring and incineration a t 550 C. While no direct relationship of ash and sulfate content was to be expected, high sulfates generally accompany high ash contents, especially in the beet sugars. O
Determination of Sulfites
The presence of sulfites in sugar is attributed solely to the use of sulfur dioxide in the process of manufacture. The methods of determining sulfites in food products, including sugar, have received extensive study in England as a consequence of the establishment by the government (8) of a maximum sulfur dioxide content permissible in foodstuffs. The official method finally adopted (7, 17) consists of distillation under prescribed conditions from acid solution in an inert atmosphere and absorption and oxidation of the sulfur dioxide to sulfuric acid, which is determined by titration. Various
ANALYTICAL EDITION
340
modifications of two other well-recognized methods are also extensively used, Ripper’s method (20) of direct titration with iodine (2, 1.2, 14) and Davidsen’s qualitative test (5) of reduction to hydrogen sulfide as developed quantitatively by Mann (1.5) and others (3, 18). These methods were studied comparatively by Spengler and Brendel ( 2 4 , by Jensen ( I S ) ,and by Coghill (4),who point out that the iodinetitratmionmethod gives results which are to be considered as maxima, owing to the presence in some sugars of other iodine absorbents. The distillation method, as shown by Mason and Walsh (16) and by Drake-Law (6) is subject to errors due to losses by oxidation by even small amounts of oxygen, and therefore it must be carried out with special precautions and strict attention to technic ( I S ) . Table 11-Sulfur
SUGAR
Trioxide a n d Sulfur Dioxide in W h i t e S u g a r s SOP Inorganic ASH Organic SO3
P. 0.m.
%
P. 0.m.
P. 9 . m.
DIRECT CONSUMPTION B E E T SUGARS
1.7
0.017 0.014 0.028 0.021 0.019 0.034 0.254 0.040 0,039 0.092 0.024 0.034 0.017 0.089 0.096 0.124 0.041 0.039 0.009 0.193
0.0 44.6 1.7 22.3 12,o 1188.4 104.6 29.2 270.1 13.7 20.6 0.0 360.1 356.7 471.4 145.8 10.3 0.0
872.9
56.3 10.2 10.0 9.1 38.4 58.6 46.1 24.3 21.0 29.4 43.4 44.2 1.1 11.8 24.1 35.9 18.0 20.2 6.1 .2o.s
2.5 1.2 0.0 0.5 3.1 0.4 6.0 0.6 1.9 4.6 3.1 4.2 0.1 1.7 1.5 0.3 0.4 1.2 0.9 3.6
DIRECT CONSUMPTION CANE SUGARS
21 22 23 24
*
0.061 0.012 0.042 0.015
294 9 24.0 44.6 19.0 REFINED
25 26 27 2s 29
0.004 0.0005 0.006 0.003 0.010
29 9 0 9 1.3 2 2
2.9
0.6 0.5 0.4 0.4 0.6
0.0 0.1 0.0 0.0 0.0
0.0
2.1 0.8
CANE SUGARS
0.0 0.0 0.0 0.0 0.0
Because of its simplicity of operation, and because it is the only one of the accepted methods by which a partition of the sulfur dioxide into its inorganic and organic .aldehydic combinations is possible (13,go), Ripper’s original methodwas chosen as the basis of the determination. One hundred grams of the sugar under examination were dissolved in 125 to 150-cc. of water in an Erlenmeyer flask, and a few cubic centimeters of starch solution were added. The solution was saturated with nitrogen gas to expel the oxygen by bubbling a rapid stream of nitrogen through the liquid for a t least 10 minutes. As soon as the stream of nitrogen was stopped, 5 cc. of sulfuric acid (1 :3) were added, and the solution was immediately and rapidly titrated with 0.01 N iodine solution to an end point which was permanent for at least 2 minutes after four or five rotations of the flask. Blank determinations on the water and reagents were similarly made. The titer of the sugar solution less that of the blank, calculated to SO2 (1 cc. of 0.01 N iodine = 0.32 mg. of SOa,or, in 100 grams of sample, = 3.2 p. p. m. of SO2),represents the sulfur dioxide present as sulfurous acid and its salts, and is designated “inorganic SO2.” For the total SO2, the same procedure was followed with the exception of the addition of 25 cc. of 1 AT potassium hydroxide solution to the sugar solution before the saturation with nitrogen, and of the addition of 10 cc. of the sulfuric acid instead of 5 cc. immediately before the titration. The titer so obtained, corrected for the iodine consumption of the reagents as found in a blank determination, and calculated as before, is the “total SO2.” The “organic” or “aldehyde SO2” is found by subtracting the value of the inorganic
Vol. 3, No. 3
SOz from that of the total SO2. The results obtained are tabulated in the fourth and fifth columns of Table 11. I n the titration of some sugars, as noted by Spengler and Brendel (24), instead of the usual deep blue end point, a fugitive violet one was observed. This is probably due to a small quantity of some interfering substance. I n such cased the end point was taken when the violet color lasted a t least 2 minutes. I n the refined cane sugars, which, so far as the authors are aware, had not been treated with sulfur dioxide during their manufacture, the small quantity of inorganic SO2indicated is, without doubt, not actually SO2, but rather an iodine-absorbing impurity (4, IS,24). Confirmation of this was indicated by titrating solutions of raw sugars from centrals which are known to use no sulfur dioxide. With these raw sugars very indefinite end points were obtained showing iodine absorbents equivalent to 19, 22, and 32 p. p. m. of SO?. At present there is no proof as to the identity of these oxidizable sdbstances, but it is suggested that they may be the polyphenols or tannins which are present in cane juice and which have already been shown to be oxygen absorbents (1). Such substances are occluded with the other non-sugars in the raw sugar and would be expected to absorb iodine. Their rate of oxidation with oxygen is rapid a t first, but slow during the later stages, which is qualitatively similar t o the rate of the iodine absorption in the raw sugars as indicated by the fugitive end point. Traces of these polyphenols have been detected in certain raw sugars by measuring the rate of absorption of oxygen by their alkaline solutions (unpublished data). Since a t present no stoichiometric relationship between the oxygen or iodine-absorbing powers of these tannins is known, their determination is impossible. Their presence in refined sugar would indicate either that they are not completely eliminated during the refining, or that other polyphenols are formed from the sugar by condensation or rearrangement under the influence of the heat used in the processes of refining. This interference introduces an error of approximately 1 p. p. m. in the determination of the inorganic SO, and the total SO2, but does not affect the organic SO2 which is found hg difference. Studies of the changes of these types of sulfur dioxide compounds during storage of sugar, and of their effett on the properties of sugar, are now in progress. Literature Cited (1) Ambler, IND. ENG CHEM, 22, 357 (1930) (2) Baissac, Intern Sugar J., 29, 538 (1927). (3) Bryan, Analyst, 63, 589 (1928). 14) Coghill, S Afrzcan Sugar J , 14, 565 (1930) ( 5 ) Davidsen, Deut Zuckerznd, 12, 939 (1887) (6) Drake-Law, Food Manufacture, 1, 21 (1927)
(7) Great Britain Ministry of Health, Reports on Public Health and Medical Subjects, No 43, 1927. (8) Great Britain Ministry of Health, Statutory Rules and Orders, No 775,
1925. (9) Great Western Sugar C o , “Methods of Analysis and Laboratory Control,” p 11, Great Western Sugar Co , Denver, Colo , 1920 (10) Great Western Sugar Co., Ibzd , p. 136 (11) Great Western Sugar Co , Ibzd , p 144 (12) Hurst, Trop. Agr (Trznzdad), 4, 66 (1927) (13) Jensen, Food Manufacture, 1, 47 (1927) (14) Jensen, Analyst, 63, 133 (1928) (15) Mann, Intern %gar J , 28, 647 (1926) (16) Mason and Walsh, Analyst, 63, 142, 144 (1928) (17) Monier-Williams, Ibzd , 62, 343, 415 (1927) (18) Ogilvie, I n f e r n Sugar J , 28, 644 (1926) (19) Pachlopnik, Z Zuczerznd cechoslovak R e p , 50, 269, 281 (1926). (20) Ripper, J . prakt Chem , 121, 46, 428 (lS92). (21) Rumpler, “Die Nichtzuckerstoffe der Ruben,” p 33, Vieweg, Braunschweig, 1898. (22) Spencer-Meade, “Cane-Sugar Handbook,” pp 11 and 14,Wiley, 1929 (23) Spencer-Meade, Ibzd , p 396 (24) Spengler and Brendel, Z Ver. deut Z u c k e r z n d , 77 (NF64), Tech Ted, 167 (1927)
