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The back titration should require about 2 ml of thiosulfate. If the titer exceeds this, it is probable that over oxidation has occurred; if less, an insufficiency of iodine has been added. It is therefore advisable in such instances to repeat the analysis and to use more or less of the reagents, as indicated by the trial analysis.

A small amount of the lactone of the sugar acid is found after acidification, which will result in a fading end point with phenolphthalein. However, when the titration is carried out in a stoppered flask and the alkali is added slowly, a pink color which persists for 1 minute or longer may be taken as the end point.

Lothrop and Holmes method for the determination of dextrose and levulose in honey by the iodine-oridation method.-Lothrop and Holmes [74] have recommended a procedure which is essentially the same as that of Willstäter and Schudel but specifically adapted to the analysis of honey. They recognized that levulose was slightly oxidized under the conditions of analysis, but the amount of oxidation was found to be an approximately constant percentage (1.2) of the levulose present and permitted the application of an empirical correction. The oxidation of levulose was found to vary rapidly with temperature, and hence the correction applied is valid only for 20° C. Total reducing sugar was determined by the Munson and Walker method and calculated as dextrose. The results agreed with the analysis by the Lane and Eynon volumetric method. In the following detailed procedure, the italicized words have been added to the original text.

To 20 ml of a solution containing 0.2 g of honey add 40 ml of 0.05 N iodine solution, using a 250 ml Erlenmeyer flask. Run in 25 ml of 0.1 N sodium hydroxide slowly and with continuous agitation, stopper, and allow to stand 10 minutes at a temperature of 20° C. Acidify with 5 ml of 2 N sulfuric acid and titrate at once with 0.05 N sodium thiosulfate, using starch indicator. The weight of dextrose in grams (not corrected for reduction of iodine by levulose) is found by multiplying the milliliters of 0.05 N iodine reduced by 0.004502. Calculate as follows:

LA approximate percentage of levulose,

R=percentage of total reducing sugars calculated as dextrose (Munson and Walker),

=

D, percentage of apparent dextrose (iodometric),
L=true percentage of levulose,

D =true percentage of dextrose.
Then introducing numerical values,

LA=1.081 (R-D1)
D=D,-0.012 LA
L=1.081 (R-D),

in which the factor 1.081 is the reciprocal of 0.925, the reducing ratio of levulose to dextrose at the nearly constant concentration of reducing sugars specified by the method.

(f) HINTON AND MACARA CHLORAMINE-T METHOD FOR THE DETERMINATION OF ALDOSES [75]

A solution of Chloramine-T behaves like sodium hypochlorite in producing hypoiodite and a certain amount of free iodine when excess potassium iodide is added. It is believed that the reaction takes place

through an intermediate hydrolysis of the Chloramine-T to hypochlorite. The reactions which appear to occur are indicated by the following equations:

C;H;SO,Na.NCl+H,O→C,H,SO,H.NH+NaClO

NaCIO+KI→NaCl+KIO

KIO+KI+H2O→2KOH+I2 (to a small extent before acidi

fication).

The hypoiodite can be used for the oxidation of aldoses.

KIO+C,H,O,CHO=CHO COOK+HI.

11

11

Upon acidification, the iodine equivalent of the unaltered ChloramineT, and any unused hypoiodite can be determined by means of thiosulfate.

C,H,SO2Na. NC1+2HC1+2KI→C,H,SO2H. NH+NaCl+2KCl+I2.

This oxidation proceeds more slowly than when alkaline iodine solution is used and hence it is more easily controlled.

Reagents.-0.05 N Chloramine-T solution containing 7.04 g/liter freshly prepared and protected from the light. Standard sodium thiosulfate solution, preferably slightly stronger than 0.05 N.

Sodium hydroxide solution, 0.5 N.
Sodium hydroxide solution, 0.1 N.
Potassium iodide solution, 10 percent.
Soluble starch solution.

Procedure.-Pipette 20 to 25 ml of sugar solution containing about 0.1 g of sugar, into a 250-ml Erlenmeyer flask. Add 20 ml of 10-percent KI solution and 0.8 ml of 0.5 N sodium hydroxide followed by 50 ml of 0.05 N Chloramine-T solution. Close the flask with a rubber stopper and allow it to stand 11⁄2 hours in a water bath at 17.5° C. Acidify with 10 ml of 2 N HCl and titrate at once with standard sodium thiosulfate solution.

1.410 g of iodine-1 g of dextrose.
0.706 g of iodine-1 g of lactose.

.710 g of iodine-1 g of invert sugar.

Sucrose has little effect on the oxidation of aldoses except in mixtures where there is only a small amount of the aldose present. Levulose, although unaffected in neutral solution under the conditions given above, has an apparent iodine equivalent of 0.007. This method has been studied by the authors in its application to condensed milk.

9. REFERENCES

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[6] F. A. Quisumbing and A. W. Thomas, J. Am. Chem. Soc. 43, 1503 (1921). [7] F. J. Bates and R. F. Jackson, Bul. BS 13, 83 (1916) S268.

[8] M. Somogyi, J. Biol. Chem. 70, 599 (1926).

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[10] J. H. Lane and L. Eynon, J. Soc. Chem. Ind. 42, 143T, 463T (1923).

[11] L. S. Munson and P. H. Walker, J. Am. Chem. Soc. 28, 663 (1906).

[12] R. F. Jackson, C. G. Silsbee, and M. J. Proffitt, BS Sci. Pap. 20, 587 (1926) S519.

[13] L. D. Hammond, J. Research NBS 24, 579 (1940) RP1301.

[14] F. Allihn, J. prakt. Chem. 2, 22, 46 (1880).

[15] F. Allihn, Z. Ver. Rübenzucker Ind. 32, (N. F. 19) 606, 865 (1882).

[16] M. G. Bertrand, Bul. soc. chim. 35, 1285 (1906).

[17] A. Herzfeld, Z. Ver. Rübenzucker Ind. 35, 1002 (1885).

[18] Browne's Handbook of Sugar Analysis, p. 428 (John Wiley & Sons, New York, N. Y., 1912).

[19] J. Vondrak, Z. Zuckerind čechoslovak. Rep. 58, 1 (1933).

[20] E. Hiller, Z. Ver. deut. Zucker-Ind. 39, 735 (1889).

[21] H. T. Brown, G. H. Morris, and J. H. Millar, Allen's Commercial Analysis, 5th ed., 1, 397 (1923) (G. Blakestons Sons & Co., Philadelphia, Pa.); J Chem. Soc. 71, 94 (1897).

[22] S. Sherwood and H. Wiley, Bul. U. S. Bur. Chem. 105, 120.

[23] A. Wedderburn, J. Ind. Eng. Chem. 7, 610 (1915).

[24] J. A. Scherrer, R. K. Bell, and W. D. Mogerman, J. Research NBS 22, 697 (1939) RP1213.

[25] W. C. Bray and G. M. J. MacKay, J. Am. Chem. Soc. 32, 1207 (1910). [26] P. A. Shaffer and A. F. Hartmann, J. Biol. Chem. 45, 349, 365 (1921). [27] Official and Tentative Methods of Analysis of the Association of Official Agricultural Chemists, 5th ed. (1940).

[28] H. W. Foote and J. E. Vance, J. Am. Chem. Soc. 57, 845 (1935).

[29] Fr. Mohr, Z. anal. Chem. 12, 296 (1873).

[30] N. Schoorl and A. Regenbogen, Z. Ver. deut. Zucker-Ind. 67, 563 (1917). [31] R. M. Fowler and H. A. Bright, J. Research NBS 15, 493 (1935) RP843. [32] H. A. Bright, J. Research NBS 19, 691 (1937) RP 1057.

[33] R. F. Jackson and J. A. Mathews, BS J. Research 8, 424 (1932) RP426. [34] G. H. Walden, L. P. Hammett, and R. P. Chapman, J. Am. Chem. Soc. 55, 2649 (1933).

[35] R. F. Jackson and E. J. McDonald, J. Research NBS 22, 237 (1941) RP1417; J. Assn. Official Agr. Chem. 24, 767 (1941).

[36] J. H. Lane and L. Eynon, J. Soc. Chem. Ind. 42, 32T, 143T, 463T (1923) 44, 150T (1925); 46, 434T (1927); 50, 85T (1931).

[37] G. H. Morris, J. Inst. Brew. 4, 162 (1898).

[38] F. M. Scales, J. Ind. Eng. Chem. 11, 747 (1919).

[39] H. S. Isbell, W. W. Pigman, and H. L. Frush, J. Research NBS 24, 241 (1940) RP1282.

[40] N. Schoorl, Chem. Weekblad. 9 (1929). Handboek Methoden van Onderzoek bij die Java-Suikerindustrie, p. 378 (1931).

[41] R. Ofner, Z. Zuckerind. čzechoslovak Rep. 59, 52, 63 (1934).

[42] O. Spengler, F. Tödt, and M. Scheuer, Z. Wirtschaftsgruppe Zuckerind. 86, 323 (1936).

[43] G. Luff and N. Schoorl, Handboek Methoden van Onderzoek bij die JavaSuikerindustrie (1931). Proc. Ninth Session, International Commission for Uniform Methods of Sugar Analysis, Int. Sugar J. 39, 1s-40s (1937). [44] P. A. Shaffer and A. F. Hartmann, J. Biol. Chem. 45, 377 (1921).

[45] M. Somogyi, J. Biol. Chem. 70, 599 (1926).

[46] S. R. Benedict, J. Biol. Chem. 68, 759 (1926).

[47] O. Folin and H. Wu, J. Biol. Chem. 38, 81 (1919); 41, 367 (1920).
[48] H. C. Hagedorn and B. N. Jensen, Biochem. Z. 135, 46 (1923).
[49] B. F. Miller and D. D. Van Slyke, J. Biol. Chem. 114, 584 (1936).
[50] P. A. Shaffer and R. D. Williams, J. Biol. Chem. 111, 707 (1935).
[51] D. D. Van Slyke and J. A. Hawkins, J. Biol. Chem. 79, 739 (1928).
[52] D. D. Van Slyke and J. M. Neill, J. Biol. Chem. 61, 523 (1924).
[53] O. Folin, J. Biol. Chem. 77, 421 (1928).

[54] J. A. Hawkins, J. Biol. Chem. 84, 80 (1929).

[55] H. Main, Int. Sugar J. 34, 213 (1932).

[56] H. C. S. de Whalley, Int. Sugar J. 39, 300 (1937).

[57] H. T. S. Britton and L. Phillips, Analyst 65, 18 (1940).

[58] W. L. Daggett, A. W. Campbell, and J. T. Whitman, J. Am. Chem. Soc. 45,

1043 (1923).

[59] J. B. Niederl and R. H. Müller, J. Am. Chem. Soc. 51, 1356 (1929). [60] H. Tryller, Int. Sugar J. 34, 353 (1932).

[61] Ph. Biourge, Bul. assn. étud. école supér. brasserie univ. Louvain. 1898).

(Jan.

[62] L. Nyns, Sucr. Belge 44, 210 (1924). Bul. assn. étude. école supér. brasserie univ. Louvain 25, 63 (1925). Chem. Abst. 19, 1236 (1925).

[63] R. F. Jackson and J. A. Mathews, BS J. Research 8, 422 (1932) RP426. [64] C. L. Hinton and T. Macara, Analyst 56, 286 (1931).

[65] C. Barfoed, Z. anal. Chem. 12, 27 (1873.)

[66] G. Steinhoff, Spiritusind, 56, 64 (1933).

[67] K. Sichert and B. Bleyer, Z. anal. Chem. 107, 328 (1936).

[68] G. W. Monier-Williams, Ministry of Health Reports in Public Health and Medical Subjects, No. 5.

[69] C. S. Slator and S. F. Acree, Ind. Eng. Chem., Anal. Ed., 2, 274 (1930). [70] G. Romijn, Z. anal. Chem. 36, 18, 349 (1897).

[71] G. M. Kline and S. F. Acree, BS J. Research 5, 1063 (1930) RP247; Ind. Eng. Chem., Anal. Ed., 2, 413 (1930).

[72] R. Willstäter and G. Schudel, Ber. deut. chem. Ges. 51, 780 (1918). [73] N. F. Goebel, J. Biol. Chem. 72, 801 (1927).

[74] R. E. Lothrop and R. L. Holmes, Ind. Eng. Chem., Anal. Ed., 3, 334 (1931). [75] C. L. Hinton and T. Macara, Analyst 52 669 (1927).

X. ANALYSIS OF SUGAR MIXTURES

1. INTRODUCTION

For the analysis of a sugar mixture it is generally necessary to have as many different analytical processes as there are sugars. These methods should be selected in such a way that the most varied properties of the sugars are represented. A consideration of some of these properties follows.

Total sugar.-In a relatively few instances, total sugar can be determined in a mixture by densimetric, refractometric, or desiccation methods. Obviously, such methods can be applied only to solutions uncontaminated with nonsugars. The densities and refractive indices of the pure constituents must be known, and in most instances it must be assumed that the properties of the mixture are in linear relation with those of the constituents. In crude materials these methods are more frequently used for the determination of total dry substance than for total sugars and thus are contributory to the determination of purity.

Polarizing power. This property can be expressed in terms of specific rotation for a monochromatic wave length or as the rotation per gram in 100 ml, in terms of the saccharimetric scale, or as the ratio of the specific rotation of the sugar in question to that of sucrose. For many sugars the specific rotation varies appreciably with concentration, and the tendency at present is to select the concentration of total substance rather than the partial concentration of each sugar in assigning the value of the specific rotation for the calculation. The specific rotations of the sugars are tabulated on page 563.

Reducing power. For the purposes of calculation, it is convenient to state the reducing powers of the various sugars in terms of that of dextrose. The "reducing ratio" may be defined as the ratio of weights of dextrose to the sugar in question which produce the same weight of reduced copper. Thus by the Allihn method, 240 mg of levulose is required to reduce the same weight of copper as 219.5 mg of dextrose. The reducing ratio of levulose is then 0.915. In the study of starch and its scission products, maltose is frequently used as the unit of

reducing power. In some cases levulose is taken as the sugar of unit reducing power.

Usually the reducing ratios of dextrose to the various sugars vary somewhat with the concentration of sugar. Thus Jackson [1], using the Munson and Walker method, found that the reducing power of levulose varied from 0.912 for 89 mg of copper to 0.937 for 375 mg of copper. With the Allihn method, the ratios appear to be more nearly independent of concentration. Browne [2] found the following reducing ratios for the Allihn method: Levulose 0.915; arabinose, 1.032; xylose, 0.983; galactose, 0.898; invert sugar, 0.958. The ratios for the more common sugars can, for the Munson and Walker method, be calculated from table 78, p. 564. The most comprehensive table of reducing ratios, including both common and unusual sugars, is that of Isbell, Pigman, and Frush (table 23, p. 190), who employed a modification of the Scales method.

2. SELECTIVE METHODS

(a) RECAPITULATION OF PREVIOUSLY DESCRIBED METHODS

Many of the methods of analysis described in detail in previous chapters are selective for the respective sugars and are directly applicable to their determination when they occur in admixture with other sugars. Thus the Clerget method is selective for sucrose and raffinose and is particularly free from analytical error when invertase is used as the inverting agent.

Levulose is selectively determined by the modified Nyns procedure, as described on page 203, but in this case corrections must be applied for the slight reduction by other sugars.

Aldoses can be distinguished from ketoses by oxidation to aldonic acids in mildly alkaline solution (p. 208).

Monoses can with fair approximation be determined in the presence of reducing disaccharides by the modified Barfoed procedure (p. 206). Pentoses and pentosans upon distillation in the presence of hydrochloric acid yield furfural, which can be estimated as described on page 241.

These selective methods, as well as the general methods described above, can be combined in a great variety of ways for the analysis. of sugar mixtures. It is usually true, however, that the application of the selective methods to actual mixtures must be made with caution, since frequently unexpected complications are encountered. It is for this reason that in the following pages will be described only those applications which have been thoroughly studied.

(b) INVERT SUGAR BY POLARIZATION AT TWO TEMPERATURES

By polarization of a solution at two widely separated temperatures, invert sugar or levulose can be determined selectively in the presence of other sugars, since the levulose constituent of invert sugar possesses a high temperature coefficient, whereas the rotatory power of dextrose is independent of temperature. Browne, however, [3, p. 298], points out that 1.5 g of arabinose, 3.0 g of galactose, 7.0 g of maltose, 9.0 g of lactose, or 50 g of sucrose, in 100 ml produces approximately the same change of polarization with change of temperature as 1 g of levulose or 2 g of invert sugar. In some instances, the

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