AnaL Chem. 1983, 55, 583-584
cause time, rather than three-dimensional space, is used to control the injected sample volume. As an injection variable, time is far easier to control accurately than distance, particularly with the aid of a computer. The timing sequence may be readily automated by using either pneumatically or electrically actuated valves. Thus, the "heart-cut" injection technique described herein may be an important step toward the routine analytical application of microcolumn HPLC. ACKNOWLEDGMENT The fused-silica capillary tubing utilized in this investigation was obtained through the courtesy of Kenneth Mahler and Ernest Dawes of Scientific Glass Engineering, Inc. LITERATURE C I T E D (1) DiCesare, J. L.; Dona, M. W.: Atwood, J. G. J. Chromatogr. 1981, 277, 369-386. Novotny, M. Anal. Chern. 1981, 53, 1294A-1301A. Scott, R. P. W.; Kucera, P. J. Chromatogr. 1979, 769, 51-72. Tsuda, T.; Novotny, M. Anal. Chem. 1978, 50, 271-275. Ishii, D.; Takeuchi, T. J. Chromatogr. Scl. 1980, 78, 462-472. Martin, M.; Eon, C.; Guiochon, 0 . J. Chromatogr. 1975, 708, 229-24 1. Tsuda, T.; Nakagawa, G. J. Chromatogr. 1980, 799, 249-258. Yang, F. J. J. Chromatogr. 1982, 236, 265-277. Takeuchi, T.; Ishii, D. HRC CC, J. Hlgh Resoluf.Chromatogr. Chromafogr. Commun. 1981, 4 , 469-470.
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Hirata, Y.; Novotny, M. J. Chromatogr. 1979, 786,521-5213, Tsuda, T.; Tsuboi, K.; Nakagawa, G. J. Chromatogr. 1981, 274, 283-290. Taylor, G. R o c . R . SOC.London, Ser. A . 1953, 219A, 186. Sternberg, J. C. "Advances In Chromatography"; Giddings, J. C., Keller, R. A., Eds.; Marcel Dekker: New York, 1966; Vol. 2; pp 205-270. Kirkiand, J. J.; Yau, W. W.; Stokiosa, H. J.; Dilks, C. H. J. Chromafogr. Scl. 1977, 75,303-316. Chesler, S. N.; Cram, S.P. Anal. Chem. 1971, 43, 1922-1933. Knox. J. H.; Giibetit, M. T. J. Chromatogr. 1979, 786, 405-418. Karger, B. L.; Martin, M.; Guiochon, G. Anal. Chem. 1974. .46, 1640- 1647. Coq, B.; Cretier, G.;Rocca, J. L.; Porthauit, M. J. Chromatogr. fici. 1981, 19, 1-12. Harvey, M. S.;Steams, S. D. "Liquid Chromatography in Environmental Analysis"; Lawrence, J. F., Ed.; Humana Press: Cliffon, NJ, 1982; Chapter 10. McGuffin. V. L.;Novotny, M. J. Chromatogr., In press. Henion, J. D. J. Chromafogr. Sci. 1981, 79, 57-64. McGuffin, V. L.; Novotny, M. J. Chromatogr. 1981, 278, 179-187. Hirata, Y.; Lin, P. T.;Novotny, M.; Wightman, R. M. J. Chromatog./ Homed. Appl. 19130, 787, 287-294.
RECEIVED for review July 21, 1982. Accepted November 114, 1982. This research was supported by the Department of Health and Human Services, Grant No. GM 24349. V.L.IM. was the recipient of a full-year Graduate Fellowship from the American Chemical Society, Division of Analytical Chemistry, which was sponsored by the Upjohn Co.
Determination of Anionic Surfactants in Presence of Cationic: Surfactants by Two-Phase Tit ration Masahfro Tsubouchi" Laboratory of Chemistry, Kochi Medical School, Oko, Nankf~ku,Kochi 78 1-5 1, Japan
Yuroku Yamamoto Deparfment of Chemistry, Faculty of Science, Hiroshima University, Hiroshima 730, Japan
Ionic surfactants are widely used in both industrial and medical applications. Anionic surfactants (AS) are precipitated by the addition of cationic surfactants (CS),but the fine turbidity is scarcely deposited in sewage or drainage samples, cases where the concentration is low. It is necessary t o determine total AS in the presence of the fine turbidity in water. Two-phase titration is one of the most frequently used methods for the determination of AS. However, it is generally difficult to determine total AS in the presence of CS because CS is used as a titrant (1,2).This paper presents a titrimetric method for the determination of total AS or CS in mixtures. EXPERIMENTAL SECTION Apparatus. A 25-mL buret was used. Materials. Solutions of cationic surfactants were prepared by dissolving zephiramine (tetradecyldimethylbenzylammonum chloride), benzethonium (benzyldimethyl[2-[2-[4-(1,1,3,3-tetramethylbutyl)phenoxy]ethoxyJethylJammoniumchloride), and R = CBH1,-C18H97). They benzalkonium (C6H5CH2N(CH3)2RCl, were standardized according to the official titrimetric method (3) using Methyl Orange as an indicator and used after accurate dilution. Solutions of anionic surfactants were prepared by dissolving sodium dodecyl sulfate, sodium dodecyl benzenesulfonate, and Aerosol OT (sodium bis(2-ethylhexy1)sulfosuccinate). They were standardized according to the official titrimetric method ( 4 ) using Methylene Blue as an indicator and used after accurate dilution. A 0.02 M solution of tetraphenylboron sodium salt wm checked according to the official gravimetric method (5)#andused after accurate dilution. Victoria Blue E3 (color was dissolved in ethanol to make a index: 44045,C33H32N3C1) 0.01% solution; it was used as an indicator. A pH 9.0 buffer solution WHS prepared by mixing 0.3 M sodium dihydrogen phosphate solution and 0.05 M sodium borate solution. All
reagents used were from Wako Pure Chemical Ind. (Tokyo, Japan). Procedure A. To 10 mL of a AS and CS mixture, each at (1-12) X 10" M concentration (AS > CS) in a 300-mL Erlenmeyer flask, were added 5 mL of buffer solution (pH 9.0), 1-2 drops of the indicator, and 3 mL of 1,2-dichloroethane. The mixture was titrated with a standard CS solution ( 5 X M or 1 X lo4 14) with vigorous shaking after each addition, until a color change from blue (Arna = 615 nm) to red,,A,( = 505 nm) took place in the organic phase. 1 mL of 1 X M titrant = 1 mL of the difference (AS - CS)(l x hl) Procedure B. To 10 mL of the same sample solution, as in procedure A, were added 5 mL of 6 N sodium hydroxide solution, 1-2 drops of the indicator, and 3 mL of 1,2-dichloroethane. The mixture was titrated with a standard solution of tetraphenylborate or 1 X (5 X M') in the same way as in procedure A, until a color change from red to blue took place in the organic phase. 1 mL of 1 X M titrant = 1 mL of 1 X M CS independent of AS present The totalconcentration calculated from the two titres in procedwe A and B corresponds to the total amount of AS. R E S U L T S AND DISCUSSION With a 5 X W5M[titrant, a blank titration is necessary because the color change at the end point is not sharp. The aqueous phase remains colorless throughout the titration in both prrocedures, due to the insolubility of the Victoria Blue B in alkaline water. 'The titre was constant between pH 8.5 and 9.5 in procedure A. In procedure B, the best color change and most constant titre were obtained a t a concentration of
0003-2700/63/0355-0583$01.50/00 1983 American Chemical Society
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Anal. Chem. 1983, 55, 584-585
Table I. Determination of AS and CS in Mixtures mixture ( 6 mL) found 10-5[CS], 10-5[AS], 10-5[CSl, 10-5[AS1, M M M M 8.60
8.70 10.8 10.9 10.8 4.40 11.1 4.30 8.60 10.8 8.12 11.0a 2.15 5.40 2.20 5.53 4.30 5.40 4.35 5.52 a Mean of 10 titrations with a standard deviation of 0.15
x 10-5 M.
sodium hydroxide from 0.5 to 2.5 N at the end point in the aqueous layer. Chloroform did not give a sharp end point. On the basis of these results, both procedures A and B are recommended. CS-AC ion pair (fine turbidity) in sample solution is extracted (dissolution) into dichloroethane. Only residual AS (AS uncombined with CS) is titrated at pH 9. The indicator combined with AS is replaced by excess of CS titrant to form an CS-AS ion pair at the end point. The titre in procedure A corresponds to free AS. In procedure B, the extracted CS-AS ion pair is decomposed by tetraphenylborate titrant and the CS-tetraphenylborate ion pair is formed. In the presence of 0.5-6 N sodium hydroxide solution, the indicator does not react with AS. An indicator-tetraphenylborate ion pair is formed at the end point. The titre in procedure B corresponds to the total amount of CS independent of AS. The total concentration of free AS in procedure A and CS in procedure B corresponds to the total amount of AS present. The method retains its validity only in cases where the concentration of CS is lower than that of AS.
The results of the determination of dodecyl benzenesulfonate in the presence of Zephiramine, shown in Table I, indicate a relative error of 2-3%. Nonionic surfactants (0.005%) disturb the end point in procedure B, because the reaction of indicator with titrant may be retarded by nonionic surfactants in alkaline solution. The following ions did not interfere at the lo4 M level in both procedures; K+, Zn2+,A13+, NH4+,NO3-, C1-, Br-, Sod2-, Si032-, and oleate. Benzethonium and benzalkonium are used as a disinfectant and anionic surfactants as a detergent in an infirmary. Sewages from a disinfecting room in the infirmary were titrated. One of the samples was 3.35 X M CS and 6.04 X M AS, vis-a-vis 2.51 X M AS by an alterative spectrophotometric method (6) using Methylene Blue. A recovery test using 2 mL of a 9.80 X M dodecyl sulfate yielded a result of 102%. In another sample, the concentration of CS was higher than that of AS. A known amount of dodecyl M) was added benzenesulfonate solution (5mL of 4.30 X to this sample (5 mL), and it was then titrated by this proM CS and 6.46 X cedure. The results were 4.17 X M AS, and it indicates 2.16 X M AS in this sample. Registry No. Zephiramine, 139-08-2;benzethonium chloride, 121-54-0; sodium dodecyl sulfate, 151-21-3; sodium dodecyl benzenesulfonate, 25155-30-0.
LITERATURE CITED (1) Reid, V. W.; Longman, G. F.; Heinerth, E. Tenside 1967, 4, 292-304. (2) Li, P.; Rosen, M. J. Anal. Chem. 1981, 53, 1516-1519. (3) "The Japanese Pharmacopoeia", 9th ed.: Hirokawa Publlshing: Tokyo, 1976; p C-317. (4) Pharmaceutical Society of Japan "Standard Methods of Analysis for Hygienic Chemist": Kinbara Publishing: Tokyo, 1980; p 660. (5) "The Japanese Pharmacopoeia", 9th ed.: Hirokawa Publishing: Tokyo, 1976; p 8-458. (6) Japanese Industrial Standard, JIS-K 0102, 1981.
RECEIVED for review October 12,1982. Accepted November 23, 1982.
Determination of Soluble and Insoluble Glucose Oligomers with Chromotropic Acid Mark T. Holtzapple"' and Arthur E. Humphrey2 Whitaker Laboratory No. 5, Lehigh University, Bethlehem, Pennsylvania 180 15
Lignocellulosic materials consist of a mixture of cellulose, pentosans, and lignin. The enzymatic hydrolysis of the carbohydrate fraction of the lignocellulose results in a mixture of various glucose and pentose oligomers. In order to calculate the amount of cellulose hydrolyzed, it is necessary to measure the concentration of total soluble hexoses. Generally, the hexose concentration is measured by reducing sugar assays (1-3). Pentoses interfere with reducing sugar assays. Additional error is introduced because the glucose oligomers must be calibrated against a single oligomer such as glucose. The phenol-sulfuric assay ( 4 ) overcomes this problem because the acid hydrolysis employed in the method converts all of the glucose oligomers to glucose. Therefore, glucose is a valid calibration sugar. Unfortunately, pentoses interfere with this assay. The concentration of the individual hexose oligomers 'Present address: Department of the Army, US.Army Natick R&D Labs, Natick, MA 01760. *Present address: Office of the Provost, Alumni Memorial Building, Lehigh University, Bethlehem, PA 18015.
may be measured by chromatographic methods (5-7), but these techniques are very time-consuming. As in the phenol-sulfuric assay, the Klein and Weissman chromotropic acid assay (8)hydrolyzes all of the glucose oligomers to glucose so glucose is a valid calibration sugar in this assay. Since pentoses do not interfere with this technique, it is ideally suited for measurement of the extent of cellulose hydrolysis. Unfortunately, the method requires protein free samples and it has a limited range (to 0.3 g/L). This paper describes an improvement to the Klein and Weissman technique which overcomes some of these problems.
EXPERIMENTAL SECTION Reagent. The Klein and Weissman method recommends the use of 2 g/L chromotropic acid (sodium 1,8-dihydroxynaphthalene-3,6-disulfonate, Eastman Kodak 230). Unfortunately, this method is subject to error due to the presence of protein in the solution. If the chromotropic acid concentration is increased, the effect of protein interference is markedly reduced. For example, the error introduced by 2.5 g/L bovine serum albumin (BSA) protein is 11%,4 % , and 0.5% for 2, 10, and 20 g/L
0003-2700/83/0355-0584$01.50/0$2 1983 American Chemical Society
