V O L U M E 23, NO. 12, D E C E M B E R 1 9 5 1
1795
degree 01' FulBxtitution as sodiun~carboxymethylcellulose in the material to be analyzed. Probable Mechanism of Color Formation. The mechanism of the i,eartiori betn-een cellulose, and anthrone is not fully understood. .\?cording to Karrer ( 5 ) .anthrone reacts with aldehyde 01' ketone group.. Sattler and Zerban (8) postulated that the waction with sugars involves conversion of the sugar to furfural or a furt'ural derivative by deb>-dration and ring formation. \\~olfroni.Schuetz, and Cavalieri ( I O ) demonstrated the formation of j-h?-tlroxymethylful.Eural from glucose by refluxing in neutral or. acid aqueous solution. Heuser ( 4 ) stated that t,he \.ield of gluco~cfrom the sulfuric acid hydrol>-sis of c-?llulow is R I I O U t '36';.
Table 111.
Determination of Sodium Carbox\methjlcellulose in Detergents and Soaps Original KaChlC Contenta,
%
Detergent Detergent Detergent Detergent
IiaCJIC Added
%
NaCh'lC Present,
%
NaCMC Found,
%
1.25 0.W 1.94 1.9; B 0.68 0.85 0.86 0.17 C 0.42 0.68 1.10 1.12 1.21 D 0.53 0.68 1.23 0.69 Soap E 0.69 0.6Y 0.00 Soap F 0.6Y 0.69 0.00 0.69 * Ry a n t t r o n e method, sample size 0,1000 gram (in aliquot) A
Diffrrrncr c7
/c
io.01
n oo
f0.02
t o , 02 0.00 0.00
furfural than did the cellulose solution. I t may be that substituents in the 2 and/or 3 positions interfere with the formation of 5-hydroxymethylfurfural. Applications. Several commercial household detergents and soaps were analyzed for sodium carboxymethylcellulose by the method. A weighed amount of sodium carboxymethylcellulose TT-as added and the analysis repeated. The results, shown in Table 111, indicated substantially quantitative recovery of the added sodium carboxymethylcellulose. Interferences. Phosphates, silicates, and fatty acids appeared not to interfere with the determination of sodium carboxymethylcellulose in detergents and soaps. Carbohydrates, carbohydrate derivatives, furfural, and 5-hydroxymethylfuI.iural all give tolored complexes, anti each would interfere in the determination of another member of the group. S o other int,erferences were found here. Certain polyoxyethylene derivatives of fatt5- acids and phenols have been reported to depress color formation ( 1 ) . Sucah compounds can usually be removed from dry mixtures by extraction with anhydrous alcohol. Although the method was developed primarily for the determination of sodium carhox?.meth!.l(~ellulose in detergent mixtures. it is believed that it will be found useful for the determination of sodium carboxymethylcellulose in other mixtures and for the determination of other cellulose derivatives. LITERATURE CITED
Solutions of cellulose and of rarboxymethylcellulose in 60% sulfuric acid were heated in the boiling water bath for 15 minutes and cooled as in the analytical procedure. The ultraviolet absorption curves of these solutions were similar in shape t o that of ~-h~tlroxyniethylfurfural!with an absorption maximum a t 290 mM (Figure 6). Although the indicated yields of b-h>-droxymethylfurfural ~ w r e much below theoretical, this evidence tends t o confirm the formation of 5-hydroxymethylfurfural as an intermediate in the color-forming reaction. I t seems prob&le that ceilulose is hydrolyzed to glucose by sulfuric acid in the cold, the glucose yields 5-h-droxymethylfurfural by deb!-dration and ring formation on heating, and the 5-hydroxymethylfurfural then wa(,t.swith anthrone to give the color. The carboxymethylolutioii gavr a loiver apparent yield of 5-h>-droxyinrth>-l-
(1) C'oiiner, -4.Z.. private communication. ( 2 ) Conner, &4.Z.,and Eyler, R. TV., AN-AL.CHEM.,22, 1129 (1950). (3) Dreywood, R., ISD.Eso. CHEM.,Asar. ED.,18, 499 (1946). (4) Heuser, Emil, "Cellulose Chemistry," p. 520, Xew York, John Wiley & Sons, 1944. (5) Karrei., Paul, "Organic Chemistry," p. 405, ?;em T o r k . Nordeman Publishing Co., 1938. (6) Morse. E. E., ASAL. CHEY..19, 1012 (1947). (7) Samsel, E. P., and DeLap, R. A . , I b i d . . 23, 1795 (1951). (8) Rattler. L.. and Zerban. F. IT., Science, 108, 207 (1948). (9) Viles, F. .J.. ,Jr., arid Silrerman, L.. - 4 s . k ~ . CHEZI.,21, 950 (1949). (10) TTolfrom, 11. L.. Schuetz. R. D., and Caralieti, L. F., J . Am. C'hem. Soc., 70, 514 (1948). RECEIVED M a y 19, 1931. Presentpd before the Analytical Chemistry Division of the Third Delaware Chemistry Symposiuni. Delaware Section, AMERICANCHEMICAL SOCIETI-.University of Delawnrr, S e w a r k . Del., J o n r u r v 13, 1951.
Colorimetric Determination of Methylcellulose with Anthrone E. P. S.IMSEL AUD R. A. DEL-IP The Dow Chemical Co., Midland, Mich.
T
HE rapidly increasing commercial importance of methyl-
cellulose ( 3 ) makes desirable the development of a colorimetric method to be used in conjunction with the well-known alkoxy1 determination ( 1 , 7 ) . Methods have been developed for the identification of this paiticular cellulose ether when it is found incorporated with other mnteiiale such as starch, gums, emulsions, and suspensions. Methocel ( D o x meth: lcellulose) is an ether of cellulose formed by interaction of methyl rhloride and cellulose n hich has been saollen by treatment with a strong base. TWOtypes are available, a water-soluble material and an alkali-soluble material; the latter has a lower degree of substitution. The tests described herein are applicable to both types, but unless specifically mentioned, the water-soluble type is meant. The Tvater-soluhle ma-
terial is a white, odorless, tasteless powder n-hich is soluble in cold water, but soluble to only a very slight degree in hot water, an interesting and unusual property. The solubility of the several viscosity grades in hot 1%-aterwas studied. Methocel is insoluble in most saturated salt solutions and most organic solvents. Methylcellulose (6) can be separated from starches and gums by first dissolving in water and then adding alcohol to throw out these materials. T e a k acids or alkalies may be added to remove interfering substances. Water-soluble impurities may be separated from methglcellulose by hot water extraction. Sodium carboxymethylcellulose, being soluble in hot water, can be extracted from methylcellulose in this manner. The use of anthrone as a qualitative and quantitative test for
ANALYTICAL CHEMISTRY
1796 The purpose of this work was to learn the solubility of Methocel in hot water and to develop a quantitative method for its determination both in the pure state and mixed with other materials. The method was to be used in conjunction with the alkoxy1 determination. A colorimetric method was developed for the determination of Methocel with anthrone and was used to test the solubility of Methocel in water at 85" and 95' C. There was very little difference in
carbohydrate materials is a relatively recent addition to the few general tests now in use. Dreywood ( 4 )initially suggested the use of this reagent as a qualitative test for carbohydrates, and obtained a positive test for eighteen carbohydrate materials. In the presence of carbohydrates, a green to blue-green color developed, depending on the concentration of the material tested. Morse (6) used a 0.05'% solution of anthrone in concentrated sulfuric acid for quantitative estimations of sucrose solutions. He found that the anthrone reagent gave a more sensitive test than 1-naphthol, which has been used extensively as a test for sugars. Viles and Silverman (9) applied the anthrone reagent to the analysis of starch and cellulose. They presented spectral transmittance curves showing that a wave length of 626 mk m-as best to use for the colorimetric analysis of starch and cellulose with anthrone. They also discussed the effect of heat on color development in this test. 100
90 80 70
60 50
I
40
water solubility between the two temperatures. The higher viscosity materials were almost insoluble in water at the above temperatures. The solubility data are useful in many cases where iMethocel is to be separated from other materials that are soluble in hot water. The colorimetric method given is useful for the determination of Methocel incorporated with other materials that would interfere with the methoxy1 de termination.
As the development of color depended on the heat evolved when the reagent in conccntrated sulfuric acid was mixed with aqueous solutions, reaction tubes of definite shape and size were used to minimize errors caused by evolution of too little or too much heat. In the tests made on methylcellulose, 20 X 160 mm. tubes were used. All color transmittances were measured with a Beckman spectrophotometer (;\lode1 B ) with a reagent blank in the reference cell, made by adding 10 ml. of anthrone reagent to 5 ml. of distilled water. The anthrone was obtained from the Sational Biochemical Co., Chicago, Ill., snd was used without purification. ANALYTICAL PROCEDURE
All reagents are of reagent grade unless otherwise noted. Anthrone Reagents. Sulfuric acid, 95%. Anthrone solution. Dissolve 0.05 gram of anthrone in 100 m!. of 957, sulfuric acid. Allow to stand a t least 4 hours before using. Procedure. Pipet 1 ml. of the methylcellulose solution ( 3 )to be tested and 4 ml. of distilled water into a teet tube which ie 19 to 25 mm. in diameter. Add 10 ml. of 0.05% anthrone solution, mix well, and allow to stand for 10 minutes. Measure the color transmittance of the solution, using the 625 mp wave length on the Beckman spectrophotometer (Model B), standardized a t 100% transmittance using a reagent blank. To make the reagent blank, add 10 ml. of anthrone solution t o 5 ml. of distilled water. Determine the per cent methylcellulose from a previously calibrated curve. I t is best to work'with a solution, the concentration of which is between 100 and 500 p.p.m. of methylcellulose, EXPERIMENTAL RESULTS AND DISCUSSION
2
I
Samples of varying methoxyl content (27 to 32%) were subjected to the anthrone test, concentrations of 50 to 400 p.p.m.
3.YETHOCEL
3 4 L
I
1
!
I ,
5 100
200
I
/
400 PARTS PER MILLION
300
I
l 500
I-
l
1
]
\K6
/
600
ln
1000
a 0
5
Figure 1. Anthrone Calibration Curves for Cellulosic Materials ?!
Black ( 2 ) used the anthrone reagent to determine sodium carboxymethylcellulose in detergent mixtures. His reagent was prepared by dissolving 1 gram of anthrone in 1 liter of 95% sulfuric acid, which was diluted to 60% acid concentration before using. The method is essentially the same as the procedure presented by the authors in this article, except that a definite 15-minute heating period rather than the diluting procedure itself is employed to provide the necessary heat required to give reproducible results. The authors have applied the anthrone reagent to the quantitative determination of methylcellulose by a procedure adapted from information furnished by Schriver (8).
04
OS
g
Figure 2.
12 16 SOLUBLE METHOCEL
20
2.4
Hot Water Solubility of Various Viscosity Grades of Methocel
V O L U M E 23, NO. 1 2 , D E C E M B E R 1 9 5 1
1797
heing tested. The average transmittances were plotted against concentrations, giving a straight-line curve. The greatest deviation from the average transmittances amounted to 20 p.p.m. The results are shown in Table I and Figure 1. Deviations from the average curve were found to be greatest a t a concentration of 400 p.p.m. and least a t a concentration of 50 p.p.ni.
By utilizing the 95” C. solubility curve (Figure 2) a correction of f$% was added to each of the calculated hlethocel values (Table ‘A,.
I n analyzing the data found in Table 11, several interesting facts are apparent. Three of the mixtures tested show a deviation of 3% or more from a 100% recovery of methylcellulose, whereas
___ An alkali-soluble m e t h y 1c el 1 ul o s e s a m p l e [llethocel AS (Dow alkali-soluble methylcelluTable 11. Recovery of Methylcellulose from Mixtures lose)] with a 12.8% methoxyl content, was also Rlixture 2nd hlethocel Found subjected to the anthrone test. .4s this sample ~. weight Component (by Difference) was insoluble in water, various weights were R-eight dissolved in separate 100-ml. portions of previtaken, taken, Found Corrected ously cooled anthrone solution, ~ ~ ~10 d d CoIlrwnent i ~ ~ grains Colnponent grams Grams . % Grains % “0 hlethocel 2.0 Sodium carboxy2.0 2.05 102.5 1 . 9 5 97.5 98.9 of the anthrone solutions to 5 ml. of distilled niethylcellulose water and mixing, the positive test for methylMethocel 2.0 Dextrose 2.0 2 . 1 4 107.0 1.86 93.0 94.4 cellulose was obtained. The curve obtained by RIethocel 2.0 Ilydroxyethyl2.0 1.98 99.0 2.02 101.0 102.4 cellulose this method had a slightly steeper slope than .\Iethocel 2.0 Carboxymethyl2.0 1.93 96.5 2.07 103.5 104.9 t h a t of the water-soluble methylcellulose, owing methylcellulose to the much lower methoxyl content. llethocel 2.0 Starch 2.0 2.10 105.0 1.90 95 96.4 Methocel 2.0 Sorbitolo 2.0 0.02 1 . 0 1.98 99 100.4 Anthrone reagent was also used to test the Methocel 2 .O llannitola 2.0 0.02 1 . 0 1.98 99 100.4 solubility of methylcellulose samples in water a t 85’ and 95’ C. Samples ranging from 15 to Sorbitol and mannitol do not give a color with anthrone reagent. 4000 cp. in viscosity were tested. ,4 25-gram ___ sample was dispersed in 1000 ml. of hot distilled water and agitated for 0.5 hour a t a constant temperature of 95’ C. The slurry was then filtered rapidly through a steam-jacketed Buchner funnel into the other four show a recovery of better than 97%. A possible a suction flask. hlethylcellulose was determined on the filexplanation for a low recovery -when sugar and starch are used a~ trate by using the anthrone reagent and the calibrated Methocel second components is that these components tend to make curve. The procedure was repeated a t a constant temperature of 85” C. methylcellulose more soluble in hot water and thus increase the amount found in the filtrate. In those mixtures in which the second component does not give a positive test with anthrone, the Results plotted in Figure 2 show the lower viscosity types t c be recovery of methylcellulose is remarkably good, indicating that soluble to the extent of 2.6%, whereas the higher viscosity types the solubility curves shown in Figure 2 can be used to good ad(above 400 cp.) are soluble only to the extent of 0.295. The vantage. The hot TTater extraction of water-soluble substances solubilities are based on the weight of dry methylcellulose. As from methylcellulose is useful when the component that is excan be observed in Figure 2, there is only a slight difference in the tracted interferes with a methoxyl determination made directly solubility of methylcellulose of a given viscosity in water a t 85” on the mixture. Such is the case when the mixture consists of and 95” C. methylcellulose plus hydroxpethylcelluloee or c,zrboxymethylmethylcellulose. Table I .
Per Cent Transmittance on Methylcellulose Samples of Varying Degrees of Substitution ( B y anthrone colorimetric procedure) OCHs, OCHI. OCHa, OCHa.
Concn., P.P.M.
OCHa,
OCHa,
27%
29%
100 50 200 300
89 76 56.5 40.0 28.0
400
29.2%
30.1%
:!
F!:
i:
51.8 38.3 27.3
56.0 37.3 28.0
52 36.5
26.5
30.3%
31%
OCHs,
OCH:,
31.4%
31.9%
;T,5 52.5 39.3 30.5
52 40 27
SUMMARY
AI-.
The anthrone method is useful for the determination of methylcellulose mixed with other carbohydrate materiale. By combining methoxyl
;i,5 ;!:; 55.5 40 29.8
___\Vhen methylcellulose of a known viscosity is to be separated from another material by a hot water extraction, the above solu-
bility curves can be utilized for correcting the methylcellulose content.
determinations, selective solubilities (particularly in hot water), and colorimetric determinatione of carbohydrates by the anthrone method, various mixtures can be analyzed successfully. I n some cases it is necessary to know what other carbohydrate and what viscosity methylcellulose are present in order to obtain most accurate results. hfethylcellulose can be determined to an accuracy of approximately 4 ~ 5 %by the above method.
52.0 38 27.5
53.3 38.9 28.2
~~
LITERATURE CITED
This was shown by further work in which several two-component mixtures consisting of Methocel and another watersoluble material were dispersed in 95’ C. distilled water and extracted and the anthrone test was made on the filtrate. I n each case the mixture was made by adding 2 grams of Methocel ( 2 5 cp. viscosity grade) to a n equal amount of sodium carboxymethylcellulose, dextrose, hydroxyethylcellulose, carboxymethylmethylcellulose, and starch. .4s these materials gave positive tests with the anthrone reagent, individual calibration curves were made for each (Figure 1). To calculate the amount of Methocel in the original mixture, the amount recovered from the filtrate was subtracted from 4 grams, the combined weight of the two components. Methocel was also dispersed with sorbitol and mannitol, materials which were still water-soluble but did not give a positive test with anthrone. To ralculate the Methocel content of these mixtures, the amount recovered from the filtrate was subtracted from 2 grams, the amount originally added.
(1) rlm. SOC. Testing Materials, “Tentative Methods of Testing
Ethylcellulose,” D 914-47T-P315-318. (2) Black, H. C., Jr., ANAL.CHEM.,23, 1792 (1951). (3) Dow Chemical Co., “Methocel Handbook,” 1949. (4) Dreywood, Roman, IXD.ENG.CHEM.,ANAL.ED.,18, 499 (1946). ( 5 ) Grant, E. H., J . Assoc. Ofic.A g r . Chemists, 2 5 , 918 (1942). (6) Morse, E. E., AS.AL.CHEM.,19, 1012-13 (1947). (7) Samsel, E. P., and McHard, J. A , , Ibid., 14,750 (1942). (8) Schriver, Ellsworth, Institute of Paper Chemistry, Appleton, Wis., ”Sorption of Water-Soluble Ethers by Cellulose,” 1950. (9) Viles, F. J., and Silverman, L., IND. ENG.CHEM.,A x . 4 ~ ED., . 21,
950 (1949). RECEIVED September 30, 1950. Presented before the Division of Analytical CHEMICALSOCIETY. Chemistry a t the 118th Xeeting of the AMERICAY Chicago, Ill.
