Anal. Chem. 1985, 57, 2091-2093
investigation of catalytic (poisoning and promotion) processes, diverse surface and the optimization Of the techniques. Registry No. Acetone, 67-64-1.
LITERATURE CITED (1) Tsuda, T.; Tokoro, N.; Ishii, D. J . Chromatogr. 1970, 46, 241-246. (2) Ettre, L. S.;Mazor, L.; Takacs, J. In “Advances in Chromatography”; Giddings, J. C., Kelier, R. A., Eds.; Marcel Dekker: New York, 1969; VOi. 8,pp 271-326. (3) Tsuda, T.; Yanagihara, H.; Ishii, 0 . J . Chromatogr. 1874, 101, 95-102. (4) Nonaka, A. In ”Advances in Chromatography”; Giddings, J. C., et al., Eds.; Marcel Dekker: New York, 1975,Vol. 12, pp 223-260. (5) Siu, K. W. M.;Aue, W. A. J . Chromatogr. 1880, 189, 255-258. (6) Parcher, J. F. J . Chromatogr. Scl. 1883, 2 1 , 346-351. (7) Bruner, F.; Bertoni, 0.; Ciccioll, P. J . Chromatogr. 1978, 120, 307-319. (8) Mangani, F.; Bruner, F. J . Chromatogr. 1984, 289, 85-94. (9) Lin, P. J.; Parcher, J. F. J . Co//old Interface Sci. 1983, 9 1 , 76-86. (IO) Bruner, F.; Clccloli, P.; Crescentini, 0.; Pistolesi, M. T. Anal. Chem. 1973, 45, 1851-1859. (11) Parcher, J. F.; Lin, P. J. J . Chromatogr. 1982, 250, 21-34. (12) Parcher, J. F.; Hyver, K. J. J . Chromatogr. Sci. 1983, 2 1 , 304-309. (13) Hyver, K. J.; Parcher, J. F. Anal. Chem. 1984, 56, 274-278. (14) Parcher, J. F.; Lin, P. J.; Johnson, D. M. Chem. Eng. Sci., in press.
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(15) Sterkhov, N. V.; Pavlov, S. S.;Ferapontov, V. A,; Chizhkov, V. P. Zh. Anal. Khim. 1982, 37, 1484-1489. (16) Sterkhov, N. V.; Pavlov, S. S.;Ferapontov, V. A.; Chizhkov, V. P. Zh. Anal. Khim. 1982, 37, 1521-1524. (17) Hoory, S.E.: Prausnitz, J. M. Chem. f n g . Sci. 1987, 22 1025-1033. (18) Steele, W. A. “The Interaction of Gases with Solid Surfaces”;Pergamon Press: Oxford. 1974;Chapter 4. (19) Suwanayuen. S.;Danner, R. P. AIChf J . 1980, 26 68-76. (20) Suwanavuen. S.:Danner. R. P. AIChf J . 1980. 2 6 . 76-83. (21j Glanz, P.; Findenegg, G. H. Adsorpt. Sci. Techno/. 1984, I, 41-50. (22) Glanz, P.; Korner, B.; Findenegg, G. H. Adsorpt. Sci. Techno/. 1984, I, 183-193. (23) Parcher, J. F.; Selim, M. I. Anal. Chem. 1979, 5 1 , 2154-2156. (24) Parcher, J. F. J . Chromatogr. 1982, 257, 281-288. (25) Laub, R. J. Anal. Chem. 1984, 5 6 , 2115-2119. (26) Hyver, K. J. Ph.D. Thesis, University of Mississippi, 1984. (27) Avgul, N. N.; Kiseiev, A. V. In “Chemistry and Physics of Carbon”; Walker, P. L., Ed.; Marcel Dekker: New York, 1970;Vol. 6. (28) Ross, S.;Oliver, J. P. “On Physical Adsorption”; Interscience: New York, 1964;p 245. (29) Chirnside, G. C.; Pope, C. 0. J . Phys. Chem. 1984, 68, 2377-2379.
RECEIVED for review February 25, 1985. Accepted M~~ 13, 1985. Acknowledgment is made to the National Science Foundation and to the donors of the Petroleum Research fund, administered by the American Chemical Society, for support of this research.
Determination of Carboxymethyl Substitution in Cellulose Ethers by Zeisel Reaction and Liquid Chromatography T. G. Miller* and R. J. Hronek’ Dowel1 Schlumberger, Post Office Box 2710, Tulsa, Oklahoma 74101
A new method has been developed for the determination of the Carboxymethyl substitution in cellulose ethers. The carboxymethyl groups are cleaved using hydriodic acld with the formation of acetic acid. The acetic acid Is quantitated using a Zorbax CB column with UV detection at 205 nm. Before quantitatlon, most of the Iodide and Iodine from the hydriodic acid must be removed due to their interference in the chromatography and detection. With the combination of oxidation and extraction, most of the iodide and Iodine Is removed. This method is applicable to the determination of carboxymethyl groups in the presence of other cellulose ether substituents. A model compound has shown reaction yields of +97%. The relative precision for 10 determinations at the 95 % confidence level for a carboxymethylcellulose (CMC) and a Carboxymethyl hydroxyethyl cellulose (CMHEC) was found to be f2.4 % and k3.0% , respectively.
Carboxymethyl celluloses have widespread applications in areas of detergents, food, pharmaceuticals, textiles, paper, ceramics, and the oil industry. The properties of carboxymethyl cellulose (CMC) and carboxymethyl hydroxyethyl cellulose (CMHEC) are largely dependent on the degree of substitution (DS) of carboxymethyl (CM) groups on the anhydroglucose unit in the cellulose. The CM content in CMC and CMHEC can be determined by several analytical procedures. These include titrimetry (1, ‘Present address: The Dow Chemical Co., Zionville Rd, Indianapolis, IN 46268. 0003-2700/85/0357-2091S01.50/0 _. ... .1 ~
2),gravimetry (3,4), and colorimetry ( 5 , 6 ) . More recently, the DS of CMC has been determined with proton nuclear magnetic resonance (7). The wet chemical techniques require several steps that are often time-consuming. The nuclear magnetic resonance (NMR) procedure works well for CMC, but CMC with other ether-substituted groups is not as applicable to the NMR technique. Determination of alkoxy1 substitution in cellulose (8)and starch (9) ethers has been reported using the Zeisel reaction with gas chromatography. In those reports, the products formed were extracted from the hydriodic acid with xylene. In the present work, the product (acetic acid) remains in the hydriodic acid and is determined by liquid chromatography after removal of interferences. The new method extends the work reported by Hodges (8)to the determination of carboxymethyl groups on cellulose ethers. The method requires no expensive equipment and should be easily applied in most analytical laboratories. EXPERIMENTAL SECTION Reagents. The CMC and CMHEC samples were obtained from Hercules, Inc. The 57% hydriodic acid, xylene, hydrogen peroxide, carbon tetrachloride, methoxyacetic acid, iodoacetic acid, and acetic acid were obtained from Aldrich Chemical Co. The acetonitrile was obtained from Burdick and Jackson. Apparatus. The Temp-Blok module heater and junior orbit shaker were obtained from Lab-Line Instruments, Inc. The 5-mL Reacti-vial with Mininert valves was obtained from Pierce Chemical Co. The chromatographic system consisted of a Waters M6000 pump, a Rheodyne Model 70-40 injection valve with a 20-pL sample loop, a Du Pont Zorbax C8 (4.6 mm x 25 cm) column, a Perkin-Elmer LC-75 spectrophotometric detector with autocontrol, and a Hewlett-Packard Model 3390A integrator. The 0 1985 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 11, SEPTEMBER 1985
nuclear magnetic resonance data were obtained with an IBM NR/80B NMR operating at 80 MHz. Chromatographic Conditions. The chromatographyof acetic acid in the present matrix was accomplished with 5% (v/v) acetonitrile in water, adjusted to pH of 3.3 with sulfuric acid, using a flow rate of 1mL/min and UV detection of 205 nm. An integrator was used to improve data precision. Sample Preparation. Approximately 100 f 0.1 mg of CMC or CMHEC was weighed in a 5-mL Reacti-vial. Subsequently, 2 mL of xylene is placed in the 5-mL Reacti-vial, and then 2 mL of 57% hydroidic acid is added. Immediately,the 5-mL Readi-vial is capped with a Mininert valve and shaken vigorously for 20-30 s. The vial is reweighed and placed in the Temp-Blok heater which has been preheated to 150 "C. With the Temp-Blok mounted onto the orbit shaker, the shaker is set at 180 rpm for 1 h. At completion, the vial is removed and allowed to cool to room temperature. The vial is reweighed to determine if any signifiicant weight loss due to leakage has occurred. The aqueous layer is transferred into a 25-mL volumetric flask. The vial is washed with three 2-mL aliquots of deionized water which is transferred to the 25-mL flask. Next, 3 mL of 10% hydrogen peroxide is added to the flask, and then the flask is filled to the 25-mL mark with deionized water. After approximately 30 min, 5 mL of the flask solution is extracted three times with 15 mL of carbon tetrachloride. After the extractions, 20 fiL of the aqueous phase is injected into the chromatograph using conditions listed previously. Since the glass vials are under pressure at elevated temperatures, the reaction should be conducted behind a safety shield in a fume hood. Also, chemical goggles and insulated gloves must be worn to prevent exposure to hydriodic acid in the event of accidental escape of reaction contents. Before calculations, the cellulosic sample weight is corrected for the percent moisture by drying approximately 1 g in a 110 "C oven for 1 h and then reweighing. The acetic acid content is determined by using an external standard. Calculations. % -CH2C02Na = 3.38
A
B
(1)
where A represents the milligrams per liter of acetic acid found and B represents the milligrams of dry sample 3.38 = 0.025L
81 X 100% 60
X
(2)
where 0.025L is the size of the volumetric flask for total amount of acetic acid, 81 is the molecular weight of -CH2C02Na(NaCM), and 60 is the molecular weight of CHBC02H.
RESULTS AND DISCUSSION The success of the present method depends on the quantitative conversion of the substituted carboxymethyl groups to acetic acid with hydriodic acid. The conversion is indicated to be occurring through the following steps:
R-O-CH2C02H
+ HI
+
R-I
+ HOCHzCO2H I
(1A)
R = anhydroglucose unit R-O-CH2COZH
+ HI
+
R-OH
HOCHzCOzH
+ HI
ICH2COzH
+ HI
+ ICHZCOZH
I1 H2O + ICHzCO2H +
I2 + CHSC02H 111
(1B) (2) (3)
Steps 1A and 1B are the Zeisel reaction of ethers, where cleavage commonly occurs on both sides of the ether oxygen (10). A mixture of the corresponding alcohols and alkyl iodides is usually obtained. In the presence of an excess of hydriodic acid, the alcohol is converted to the alkyl iodide. Any hydroxyacetic acid (I)should be converted to iodoacetic acid (11). The use of hydriodic acid sometimes results in reduction of the alkyl iodide to the corresponding alkane (11). In other
Table I. Chemical Shifts of Acetic Acid and Derivatives compound
chemical shift, ppm
CH*30CH,COZH CHSOCH*zCHzH HOCH*ZCOzH
3.38 4.12 4.24
compound
chemical shift, ppm
ICH*ZCOzH CH*&OzH
3.74 2.08
AR
I
C, 4.71 rnin
Chromatogram of Zeisel reaction of CMC showing (A) iodide, (6) iodine, and (C) acetic acid after peroxide and carbon tetrachloride treatments. Chromatographic conditions are listed in the Experimental Flgure 1.
Section.
reports (8, 91, the iodo products were extracted from the hydriodic acid in situ before reduction might occur. In the present work, the iodo product remains in the hydriodic acid. Reagent grade iodoacetic acid in hydriodic acid a t ambient temperatures was found by proton NMR to rapidly convert to acetic acid (111). Methoxyacetic acid (CH30CH2C02H)was found by proton NMR to convert to a mixture of hydroxyacetic and acetic acid which converted to only acetic acid with additional heating. No iodoacetic acid was found. The carboxymethyl-substituted celluloses showed only acetic acid after heating at 150 "C for 1 h. At temperatures below 150 "C by 10 "C or more, incomplete conversion and a mixture of I and I11 were found by proton NMR. The quantitative conversions of substituted celluloses might require higher temperatures or longer reaction times as the carboxymethyl level reaches higher values. Table I lists the proton chemical shifts for the compounds of interest for this work. The chemical shifts are corrected to a MeaSi reference using sodium trimethylsilyl propanesulfonate (-0.07 ppm) in hydriodic acid. Iodoacetic acid was run in deuterium oxide. Although Hodges (8) reported the use of an organic acid catalyst, the presence or absence of such catalyst showed no observable difference. It may be that the present method is self-catalyzed since the final product (acetic acid) is among the catalysts listed by Hodges (8). Hodges (8) and Lee (9) used xylene to extract the products before reduction might occur and to quantitate the products by gas chromatography. The product does not extract into the xylene in the present work. However, the use of xylene during the Zeisel reaction did yield slightly higher substitution values than when xylene was not present. The xylene may function by preventing loss of acetic acid from the aqueous layer or extracting iodine to allow further reaction. Likely, the xylene serves both purposes. With the product remaining in the hydriodic acid solution, the interference from the iodide and iodine must be removed to detect the acetic acid by liquid chromatography. Upon addition of hydrogen peroxide to the hydriodic acid solution, a large amount of iodine is produced with precipitation. After carbon tetrachloride extractions of the peroxide-treated solution, the acetic acid is easily observed as shown in Figure 1. The two large peaks would primarily be iodide and iodine, eluting in that order. Standards carried through the same steps as the carboxymethyl-substituted celluloses showed no
ANALYTICAL CHEMISTRY, VOL. 57, NO. 11, SEPTEMBER 1985
Table 11. % NaCM D e t e r m i n a t i o n s of CMC and CMHEC sample
Zeisel/LC
titrationa
CMC CMHEC
33.9 12.4
32.4 12.0
Triplicate determinations b y a standard apid wash procedure described in ref 1. ~~~
~
~~~~
noticeable differences in the acetic acid content. So, the standards were prepared externally in deionized water. The detector showed a linear response from 250 to 1500 mg/L which includes the concentrations for this work. If there is a lack of separation of the peaks for confident data, the peroxide step can be allowed additional time or the acetonitrile may be removed from the mobile phase. During the development and the validation work for this method, no significant change in the chromatography was observed. As with any chromatographic column, proper use and care will extend its lifetime. If there is concern about any unreacted peroxide affecting the chromatography, smaller injection volumes may be used where appropriate or the aqueous solution before injection may be heated to reduce the amount of peroxide. With the conditions in the experimental section, methoxyacetic acid gave reaction yields of +97% for the amount of acetic acid expected. The analysis of a CMC (33.9% NaCM) and a CMHEC (12.4% NaCM) showed a relative precision for 10 determinations at the 95% confidence level of f2.4% and f3.0%, respectively. Table I1 lists values of NaCM in the CMC and the CMHEC by the present and the ASTM (1) methods. In general, the Zeisel/LC method gave approximately 4% higher values than those found by the ASTM acid wash titration. This is in line with the proton NMR work of Ho and Klosiewicz (7). Presumably, the hot, hydriodic acid reacts with carboxymethyl groups that are not accessible in the titration as reported by Schleicher et al. (12). Frequently, the carboxymethyl celluloses will contain a small amount of salts including sodium glycolate (hydroxyacetate) which would be converted to acetic acid and produce
2093
falsely high values. So, it is recommended to wash the carboxymethyl celluloses with aqueous methanol to remove these salts for more confident data.
CONCLUSIONS This report describes a method which can be adapted for fast confident analyses on multiple samples in most analytical laboratories with no, or little, extra equipment. The 1-h reaction period would allow a large number of samples to be analyzed per day. By determination of reaction time and temperature, this method should be useful for other carboxymethyl-substituted carbohydrates. In addition to carboxymethyl groups, alkoxy1 groups could be determined simultaneously using the work of Hodges (8)since xylene is used in both methods. ACKNOWLEDGMENT The authors express their appreciation to H. A. Mottola, Chemistry Department, Oklahoma State University, for his constructive review in preparing this manuscript. Registry No. CMC, 9000-11-7;CMHEC, 9004-30-2;CH30CHZCOZH, 625-45-6. LITERATURE CITED ( I ) ASTM D 1439-72(78). (2) (3) (4) (5) (6) (7)
(8) (9)
(IO) (1 1)
(12)
Eyler, R. W.; Kiug. E. D.; Dlephuls, F. Anal. Chem. 1947, 79, 24-27. Conner. A. 2.; Eyler, R. W. Anal. Chem. 1950, 22, 1129-1132. Francis, C. V. Anal. Chem. 1953, 25, 941-943. Calkins, V. P. Ind. Eng. Chem., Anal. Ed. 1943, 75, 762-763. Mukhopadhyay, S.; Mltra, B. C.; Palit, S. R. Anal. Chem. 1978, 45, 1775-1778. Ho, F. F.-L.; Klosiewicz, D. W. Anal. Chem. 1980, 52, 913-916. Hodges, K. L.; Kester, W. E.; Wlederwlck, D. L.; Grover, J. A. Anal. Chem. 1979. 51, 2172-2176. Lee, Y.-C.; Baaske, D. M.; Carter, J. E. Anal. Chem. 1983, 55, 334-338. March, J. “Advanced Organic Chemistry: Reactions, Mechanisms, and Structure”; McGraw-Hill: New York, 1968; p 344. March, J. “Advanced Organic Chemistry: Reactions, Mechanisms, and Structure”; McGraw-Hill: New York, 1968; p 343. Schleicher, H.; Dantzenberg, H.; Philipp, B. Papier (Darmstadt) 1977, 3 7 , 499-503.
RECEIVED for review December 10, 1984. Resubmitted May 9, 1985. Accepted May 9, 1985.
