Iodornetrie Determination of Maltose A Rapid and Convenient Semi-micromethod for Determining Maltose in Studies of Amylase Action M. L. C4LDWELL, S. E. DOEBRELING, AND S. H. MANIAN Department of Chemistry, Columbia University, New York, N. Y.
sents the iodine reduced by the sugar and, hence, gives the equivalent of maltose present in the solution.
THF
4 method briefly presented here for the iodometric determination of reducing sugar formed in the hydrolysis of starch by amylases was developed to meet the special requirements of studies of amylase action in the presence of heavy water (5) but has proved convenient for more general use with these enzymes. The method is accurate,. precise, and rapid, requires relatively small volumes of solutions and no elaborate apparatus, and is suited to work with different amylases. This is shown by the quantitative recovery of maltose from starch dispersions of different electrolyte concentrations and hydrogen-ion activities adjusted to the conditions which favor the action of pancreatic amylase (11)on the one hand and of the amylases of barley malt (4, 12) on the other. The method is especially recommended for work with heavy water, in which the recovery of the heavy water is an important consideration, as its dilution with reagents is kept relatively low and its evaporation is decreased by the omission of such steps as boiling and filtering which are encountered in many other procedures. Previous investigators have emphasized the importance to quantitative interpretation of controlling the hydrogen-ion activity of the solutions during the oxidation of sugar by iodine (1-3, 6-8) and have proposed the use of suitable buffers (a,$,7 , 8 ) . This principle has been successfully applied in the micromethod recently developed by Linderstrom-Lang and Holter (7)for the determination of minute amounts of reducing sugar in microstudies of amylase action and has been incorporated in the method described here. The present report does not introduce new theoretical principles but unites in one convenient procedure conditions which have been found importmt by different workers.
The data presented here indicate that the maltose is quantitatively oxidized under the prescribed conditions (pH approximately 9.9) to the corresponding monobasic acid according to the following equation:
+ + 3NaOH --+
C12H22011I2
+
CI2H210i2Na 2NaI
+ 2H20
With the type of buret suggested, approximately 1 minute is required to combine the sugar solution with the buffer and the iodine, while 2 minutes are sufficient for the addition of the sulfuric acid and the titration with the thiosulfate. This makes it possible to obtain measurements of maltose at frequent intervals, 2 or 3 minutes apart, and enables one to follow the course of the formation of maltose throughout the hydrolysis of starch by amylase or to obtain strictly comparable measurements of the action of a given enzyme solution upon different substrates hydrolyzed side by side. In cases where frequent sampling of hydrolysis mixtures is desired, the aliquots of the buffer solution are pipetted into the glass-stoppered Erlenmeyer flasks before the enzyme hydrolyses are started. ACCURACY.The accuracy of the method was established by the use of a purified sample of maltose. It was found to contain 94.9 per cent of maltose when examined by the gravimetric copper-reduction method of Quisumbing and 4.00
3.60
Determination of Reducing Sugar REAQENTS.A buffer solution ( 7 ) was prepared by mixing 5 volumes of 0.2 M sodium carbonate and 1 volume of 0.4M hydrochloric acid. The sodium carbonate was purchased in the form of a highly purified and analyzed product and used without further purification. 0.05 M iodine in 2.4 per cent potassium iodide (14),0.6 M sulfuric acid, 0.05 M sodium thiosulfate, and 1 per cent starch dispersion as indicatcr. PROCIDDURE. Five cubic centimeters of the buffer solution are pipetted into a 250-cc. glass-stoppered Erlenmeyer flask. One cubic centimeter of the sugar solution (starch-hydrolysis mixture) t o be analyzed is pipetted into the buffer solution in the flask and immediately treated with 2 rc. of 0.05 M iodine fiolution which is added from a long-tipped automatic buret graduated to 0.01 cc. After gentle rotation t o insure thorough mixing, the solution is allowed to stand in the tightly stoppered flask in the dark a t room temperature for 30 minutes for the oxidation of the sugar. Variations in room temperature from 23' t o 29" do not appreciably influence the results. The time allowed for the oxidation of the sugar is, however, important and should be kept constant. At the end of 30 minutes, 5 cc. of 0.06 M sulfuric acid are added from a buret in such a manner as to wash down the sides of the flask and mix gently but thoroughly with the solution. The excess iodine is immediately titrated with 0.05 M thiosulfate which is added from an automatic long-tipped buret graduated to 0.02 cc. If no starch is present, 1 or 2 drops of a 1 per cent starch dispersion are added as indicator. The difference between the volume of thiosulfate required to reduce 2 cc. of the original iodine solution, treated as described above, and that required for the iodine which remains after the oxidation of the sugar repre-
3.20 ,j2.60 c,
.E C 240 .? . x 9
8 2.00 P 3
f.60
.80
.40
FIGURE1. RECOVERY OF
LVALTOSE FROX ITS
SOLUTIONS
AQUEOUS
Data represent thiosulfate equivalent to the iodine reduced by the maltose. Circles show experimental values; solid line, the stoichiometric values. The maltose solution contained approximately 20 mg. of anhydrous maltose per c c . The thiosulfate solution was 0.0516 M (1 cc. was equivalent to 0.0877 mg. of anhydrous maltose).
181
INDUSTRIAL AND ENGINEERING CHEMISTRY
182
Thomas (9); 95.1 per cent of maltose when examined for specific rotatory power, [a]': = 131.29' (10); and 94.9 per cent of maltose when examined by the method outlined here. PRECISION. The precision or reproducibility of the method is shown by the following typical data: Eight aliquot portions of 1 cc. each of a maltose solution which contained approximately 20 mg. of maltose per cc. were treated as described above. The 0.05 M thiosulfate required to reduce the excess of iodine which remained after the oxidation of the sugar in the different aliquots was 2.11, 2.11, 2.11, 2.11, 2.10, 2.11, 2.11, and 2.11 cc. (0.01 cc. of the thiosulfate solution used was equivalent to 0.085 mg. of anhydrous maltose). LIMITS O F CONCENTRATION OF MALTOSE.The stoichiometric relationship between maltose and iodine given above was established with 1-cc. portions of aqueous solutions of maltose which contained approximately 20 mg. of maltose per cc. By taking the experimental thiosulfate equivalent of 1-cc. portions of such maltose solutions as 100 per cent recovery of maltose, it was found that the method outlined here may be used for the quantitative determination of maltose up to 25 mg. This is shown by the experimental data and calculated values given in Table I and in Figure 1. When not more than 25 mg. of maltose are considered, the average deviation of the differences between the experimental and stoichiometric values (columns 3 and 4, Table I) is 0.01 cc. of the thiosulfate solution, equivalent to 0.0877 mg. of anhydrous maltose, Therefore the method is suitable for the determination of the amounts of maltose which are theoretically obtainable from I-cc. portions of reaction mixtures resulting from the hydrolysis of 1 or 2 per cent starch.
VOL. 8, NO. 3
tively accounted for when it was superimposed upon reaction mixtures obtained a t different stages of the hydrolysis of starch, in the presence of different concentrations and proportions of its hydrolysis products. This justifies the use of the method to follow t6e course of the formation of maltose from starch throughout its hydrolysis by amylase. TABLE11. DETERMINATION OF MALTOSE IN PRESENCE OF 2 PERCENTSTARCH ADJUSTEDTO CONDITIONS WHICHFAVOR AcTION OF DIFFERENT AMYLASES ( D a t a expressed in
00.
of 0.05 M thiosulfate required for reduction of exces8 iodine) a
1 cc. of maltose solution, alone 1 cc. of 2 per cent starch, alone 1 cc. of 2 per cent starch 1 cc. of maltose solution 0.5 cc. of maltose solution alone 1 cc. of 2 per cent starch 0.5 cc. of maltose solution
+
b
4 . 3 6 4.36 1.88 1.88
3168 3:07
1.89
..
3'i5
..
2 er cent starch adjusted t o pH 7.1. 0.01 M phosphate; 0.025 Msodium chlorize. conditions which favor the aciion of pancreatic amylase ( I f ) . b 2 pel cent starch adjusted t o p H 4.5; 0.01 M acetate; conditions which favor the action of the amylases of barley malt (4). 5
I n this connection, it is of interest to note that there is good agreement in the values obtained for reducing sugar (calculated to maltose) formed in the hydrolysis of starch by amylase when comparable reaction mixtures are analyzed by the method described above and by the gravimetric copperreduction procedure heretofore generally employed in this laboratory (11, IS). I n a typical case, proportionate volumes of a solution of pancreatic amylase reacted with 100-cc. and 5-cc. portions of 2 per cent buffered (11) starch. At the end of 30 minutes, the 100-cc. digestion mixtures, when examined by the gravimetric method, yielded 270 mg. of maltose, while 1-cc. aliquots of the 5-cc. reaction mixture gave 2.79 mg. of DETERMTNATION OF MALTOSE IN THE PRESENCE OF STARCH maltose per cc. when analyzed by the procedure described AND ITSHYDROLYSIS PRODUCTS. I n the study of amylase here. action it is important to use a method for the determination TABLE111. RECOVERY OF MALTOSE of reducing sugar which gives quantitative results in the (When superimposed on reaction mixtures a t different stages of the hydrolysm presence of starch and its other hydrolysis products, which of starch by pancreatic amylase) may be present in the reaction mixtures in any proportions Thiosulfate for Residual Iodine depending upon the conditions of the amylase experiments. Reaction Time of mixture The procedure outlined above fulfills these requirements. Hydrolysls Reaction plus 1 cc. of of Starch mixture maltose The typical data summarized in Table I1 show that the soln." Differencea by Amylase alone presence of 2 per cent starch and of the electrolytes and Mm cc . cc. cc. hydrogen-ion activities which favor the action of pancreatic 10 3.00 1.96 1.04 20 2.77 1.76 1.01 amylase on the one hand (11) and of the amylases of barley 45 2.69 1.58 1.01 malt on the other (4) do not interfere with the accurate de1.51 1.01 60 2.62 120 2.48 1 . 4 3 1 .05 termination of maltose and justify the use of the method for 1 CC. of this maltose solution alone was equivalent t o 1.01 cc. of the thiothe study of different amylases which act upon starch adjusted sulfate solution. to widely different conditions (4, 11). Moreover, the data summarized in Table I11 show that maltose was quantitaDETERMJNATION OF MALTOSE IN PRESENCE OF HEAVY WATER. Equal weights of maltose were dissolved in 100 OF MALTOSE FROM AQUEOUS SOLUTIONS per cent purified heavy water (5) and in redistilled ordinary TABLEI. RECOVERY OF KNOWN CONCENTRATION water and analyzed by the above procedure with the following results, given in cubic centimeters of 0.05 M thiosulfat,e Thioaulfate Equivalent Thiosulfate t o Maltoae Oxidized Maltose Recovered reqiiiied for the excess iodine in each case: Maltose for ExperiStoichioExperiStoichio5
Solution Used Cc. None 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1 .2 1.3
1.5
1.7 1.9 2.1
Residual Iodine
mental value
cc*
cc .
metric value Cc
4.07 3.85 3.61 3.40 3.14 2.90 2.65 2.44 2.22 2.00 1.76 1.52 1.30 1.12 0.75 0.55 0.42 0.30
0.00
0.00
0.22 0.46 0.67 0.93 1.17 1.42 1.63 1.85 2.07 2.31 2.55 2.77 2.95 3.32 3.52 3.66 3.77
.
0.23 0.46 0.69 0.92 1.16 1.39 1.62 1.85 2.08 2.31 2.54 2.77 3.00 3.47 3.93 4.39 4.86
mental valuea
metrlc value
.
Me.
Mg
0.00
0.00
1.93 4.03 5.88 8.16 10.26 12.45 14.30 16.22 18.15 20.26 22.36 24.29 25.87 29.12 30.87 32.01 33.06
2.03 4.05 6.08 8.10 10.13 12.16 14.18 16.21 18.14 20.26 22.29 24.31 26.34 30.39 34.44 38.49 42.55
a 1 cc. of the thiosulfate solution was equivalent to 8.77 mg. of maltose anhydride.
Reagents alone plus 1 cc. of ordinary water (blank) Reagents alone plus 1 cc. of 100 per cent heavy water (5) (blank) 1 cc. of a solution of maltose dispolved i? ordinary water 1 cc. of a solutlon of maltose dlssolved in 100 per cent heavy water ( 6 )
4.07, 4.07 4.07, 4.07 2.13, 2.13 2.13, 2.12
These data make it evident that the method outlined here may be used for the determination of maltose in the presence of heavy water.
Summary A rapid and convenient method for the quantitative determination of reducing sugar (maltose) formed in the hydrolysis of starch by amylases is briefly described. It is especially recommended for studies of amylase action in the presence of heavy water.
MAY 15, 1936
ANALYTICAL EDITIO?;
Literature Cited (1) Aoree and Kline, Bur. Standards J . Research, 5, 1063 (1930). (2) Auerbach and Bodlander, 2.angew. Chem., 36,602 (1923). (3) Cajori, J . B i d . Chem., 54,617 (1922). (4) Caldwell and Doebbeling, Ibid., 110,739 (1935). (5) Caldwell, Doebbeling, and Manian, J . A m . Chem. Soc., 58, 84 (1936). (6) Gobel, J . Biol. Chem., 72,801 (1927). (7) Linderstr$m-Lang and Holter, Compt. rend. trav. lab. Carlsberg, 19,No. 14, 1 (1933).
183
(8) MacLeod and Robinson, Biochem. J., 23,517 (1929). (9) Quisumbing and Thomas, J . A m . Chem. Soc., 43,1504 (1921). (IO) Sherman, “Organic Analysis,” 2nd ed., pp. 78-85, New York, Macmillan Co., 1917. (11) Sherman, Caldwell, and Adams, J. Am Chem. Soc., 50, 2529, 2535, 2538 (1928). (12) Sherman, Caldwell, and Boynton, Ibid., 52, 1669 (1930). (13) Sherman, Kendall, and Clark, Ibid., 32,1073 (1910). (14) Treadwell-Hall, “Quantitative Analysis,” Vol. 11, 6th ed., p. 554,New York, John Wiley & Sons, 1924. R B C ~ I V EJanuary D 28, 1936.
De termination of Phosphorus in Stainless Steels A Rapid Method Using Perchloric Acid CHARLES D. SUSANO‘ AND J. H. BARNETT, JR.,ZKnoxville, Tenn.
I
N THE course of recent months, the materials testing
laboratories of the Tennessee Valley Authority have been called upon to make a large number of analyses of stainless steels. Particular stress was placed upon the rapidity with which the analyses could be made. The analysis in general presented no unusual difficulties, but since time was an important factor, a more rapid method for the determination of phosphorus was sought to replace the one now in general use. The method now used requires the action of hydrochloric-nitric acid mixture to effect solution of the sample, oxidation of phosphides to phosphate, and the subsequent removal of hydrochloric acid, a t best a time-consuming operation fraught with many difficulties. Perchloric acid (60 per cent) was found to be suitable for replacing the above-mentioned acid mixture, thus eliminating the necessity of removal of hydrochloric acid. It is known that perchloric acid interferes neither with the precipitation of ammonium phosphomolybdate nor with its estimation by alkalimetric methods (6). It is shown below that phosphides in steel are completely oxidized to phosphate by the action of hot 60 per cent perchloric acid. The use of weaker concentrationti of perchloric acid is not recommended. Lundell advises that from 10 to 15 per cent of the phosphorus may be lost if a 50 per cent acid is used (6). The speed of the method lies in obviating the necessity of removing chlorides and in circumventing oxidation by nitric acid and potassium permanganate as practiced in the normal phosphorus procedure (4). It is known that perchloric acid may be: used for the removal of chlorides, when present, as hydrochloric acid in phosphorus determinations (7), but the power of perchloric acid to oxidize phosphides to phosphate has apparently not been described. The authors’ conclusions with regard to the accuracy and the precision of the suggested method are based on the results of repeated analyses of several Bureau of Standards samples and a comparison with the certified values given therewith. The data given below show close agreement with Bureau of Standards phosphorus values. To show that perchlorates do not interfere with the precipitation of ammonium phosphomolybdate, a series of determinations on pure diammonium phosphate was made in the presence of normal concentrations of perchloric acid. The results (Table 111) gave close checks with the calculated theoretical phosphorus content of the salt in each case. I n the determination of phosphate in iron ore, Willard has substituted perchloric acid for nitric acid in the procedure for the removal of chlorides after silica dehydration. He re1 2
Tennessee Valley Authority, Knoxville, Tenn. Present address, The Reilly Tar & Chemical Corp , Chattanooga, Tenn.
ports that the presence of perchloric acid introduces no error (11).
I n this laboratory, this method has resulted in more than 50 per cent saving in operator’s time in the analysis of stainless steels. Fewer losses by splattering occur and, in general, greater accuracy has been obtained. While 60 per cent perchloric acid is among the more expensive analytical reagents, the saving in operator’s time more than compensates for the additional cost. The cost of the chemicals for this method amounts to approximately 7 cents per determination.
Experimental
REAGENTS.The reagents for this method are essentially those required in the normal determination of phosphorus in steel, plus 60 per cent reagent grade perchloric acid (1). Procedure To a 2.00-gram sample placed in a 500-ml. Erlenmeyer flask, add 20 ml. of 60 per cent perchloric acid and warm to effect complete solution. Cover with a funnel, the stem of which has been removed, and boil for 30 minutes or until the chromium is completely oxidized. Here a modified still head, as described by Smith, may be used to advantage (8). The solution should be a deep red to brown color. Cool, dilute t o 100 ml., and add ammonium hydroxide (specific gravity 0.90) until a slight precipitate is formed. Approximately 12.5 ml. will be required. Dissolve the brown precipitate by the addition of nitric acid (specific gravity 1.20). Here 20 t o 25 ml. will suffice. Add 1 to 5 ml. of 1 to 10 ammonium bisulfite, sufficient to reduce the chromium and vanadium present (ferrous sulfate may be used for this reduction). Boil to remove nitrous oxide fumes and free chlorine (2). Allow the solution t o cool slightly, add 50 ml. of ammonium molybdate solution, and agitate for 5 minutes. Allow the precipitate t o settle at room temperature for 2 hours or more. Filter the yellow precipitate and wash from the containing vessel, first with 2 per cent nitric acid five to ten times to remove iron salts, and subsequently with 2 per cent potassium nitrate solution until the filtrate is no longer mid to litmus paper. Place the precipitate with the filter pa er in the original precipitation vessel, dilute with about 50 cc. oFwater, and then add 8 drops of phenolphthalein indicator. Add an excess of standard sodium hydroxide solution and agitate to effect complete solution of the yellow precipitate. Titrate the excess of alkali with standard acid solution.
If the standard solutions are adjusted to 0.149 N , 1 ml. of alkali consumed by the yellow precipitate will be equivalent to 0.01 per cent of phosphorus in the original 2.00-gram sample. The alkali was standardized against Bureau of Standards potassium acid phthalate. The acid was then,
