1444
Anal. Chem. 1987, 59, 1444-1445
(17) Douglas, D. J.; Houk, R. S. Prog. Anal. At. Spectrosc. 1985, 8 . 1-18. (18) Houk, R. S.Anal. Chem. 1988. 58. 97A-105A. (19) Gray, A. L. Spectrochim. Acta, Part6 1985, 4 0 8 , 1525-1537. (20) Tan, S. H.; Horiick, G. Appl. Spectrosc. 1986, 4 0 , 445-460. (21) Jiang, S.J.; Houk, R. S. Anal. Chem. 1986, 58, 1739-1743. (22) Jiang, S.J.; Houk, R. S. Spectrochlm. Acta. Part 6,in press. (23) Harrison, W. W.; Hess, K. R.; Marcus, R. K.; King, F. L. Anal. Chem. 1986, 58, 341A-356A. (24) Park, C. J. Ph.D. Dissertation, University of Toronto, Toronto, Ontario, Canada, 1985. (25) Arrowsmith, P.; French, J. B.; Park, C. J.; Van Loon, J. C., submitted for publication in Anal. Chem . (26) Welch, M. Lasers Appl. 1988, 5, 67-71. (27) McLaren, J. W.; Beauchemin, D.; Berman, S. S.Anal. Chem. 1987, 59,610-613. (28) Laqua, K. In Chemical Analysis; Omenetto, N., Ed.; Wiiey-lnterscience: New York, 1979; Voi. 50, Chapter 2, pp 47-118. (29) Huie, C. W.; Yeung, E. S. Anal. Chem. 1986, 58, 1989-1993.
(30) Belchamber, R. M.; Horiick, G. Spectrochim. Acta, Part B 1982, 376, 1037- 1046. (31) Bevington, P. R. Data Reduction and Error Analysls for the Physical Sciences, McGraw-HIik New Yo&, 1969. (32) Tan, S.H.; Horiick, G., submitted for publication in Spectrochlm. Acta,
Part B . (33) DeMarco, R.; Kew, D.; Sullivan, J. V. Spectrochim. Acta, Part 6 1986, 4 1 8 , 591-595. (34) Burstenbinder, J., personal communication, Statistik Software Systemtechnik GMBH, Berlin, 1986.
RECEIVED for review October 6, 1986. Accepted February 1, 1987. Presented in part at the Pittsburgh Conference and Exposition on Analytical Chemistry and Applied Spectroscopy, Atlantic City, NJ, March 1986, and at the American Society for Mass Spectrometry, Cincinnati, OH, June 1986.
Determination of Low Levels of Cationic Polyelectrolytes in Water Dennis P. Parazak,* Charles W. Burkhardt, and Kevin J. McCarthy Petrolite Corporation, 369 Marshall Avenue, St. Louis, Missouri 63119
Anionic dye complexatlon has been used to measure the concentrations of cationic polyelectrolytes in water. The colloldai form of the complex interferes with spectrophotometric measurements and must be removed. Advantage Is taken of the natural hydrophobic character of the complex to facilitate its removal with Freon.
There are a number of publications describing the quantitative determination of quaternary ammonium surfactants in water. These methods include polarography ( l ) ,chromatography (2),fluorometry (3), potentiometry ( 4 ) ,two-phase titration ( 5 ) , the colloidal titration (6), extraction-spectrophotometry (7-9), and flow injection analysis (10). Several of these methods have been applied to the determination of cationic polyelectrolytes. One of the most common methods for these polymers is the colloidal titration (11). Josephs and Feitelson (12) used a turbidimetric titration. However, for low concentrations a direct spectrophotometric method is preferred since it is more sensitive. In this area, Toei and Zaitsu (13) used flow injection analysis and Klyachko et al. (14) used a combination of fluorometry, potentiometry, and infrared spectroscopy. The method described herein is similar to that of Dey and Palit ( I @ , in that the polycation forms an insoluble charge complex with an anionic dye. The complex is insoluble in both water and organic solvents and can be removed from the test mixture. Consequent changes in the light absorbance of a standard dye solution are proportional to the mass of polyelectrolyte complexed with the dye. The major differences between this procedure and the method of Dey and Palit are that ponceau S dye is used instead of eosin A or rose bengal and the need for centrifugation to remove the colloid has been eliminated.
EXPERIMENTAL SECTION The polyelectrolytes used were poly(dimethyldially1ammonium chloride) (poly(DMDAAC)and a dimethylamineepichlorohydrin condensation copolymer (DMA/EPI) of molecular weights 2.8 0003-2700/87/0359-1444$01.50/0
X 105 and 3.3 x lo4 (by light scattering) and charge densities of 6.19 and 7.27 mequiv of quaternary nitrogen/g, respectively. These were exhaustively dialyzed, freeze-dried, and assayed by chloride content before use. Ponceau S dye was supplied by Aldrich Chemical Co. It has a dye content of approximately 75% and was used as received. Stock solutions of the polyelectrolytes were prepared and diluted with an appropriate aqueous solvent to give a series of solutions ranging in concentration from 0 to 0.7 mequiv of quaternary nitrogen/L. In order to examine matrix effects, two aqueous phasea were used. These were distilled water and distilled water with the following inorganic salts: 2.16 mequiv/L HCO,, 1.35 C1-, 1.19 Sod2-, 2.53 Ca2+, 1.32 Mg2+,0.75 Na+, 0.12 Kf. The salts used were all analytical reagent grade and used as received. This particular combination of salts was selected to duplicate Mississippi River water sampled in the New Orleans area in late 1984 and is designated reconstituted Mississippi River water. Traces of boron, aluminum, barium, nickel, silver, and strontium also found in this water sample were not added. Ten-milliliter aliquots of the stock polyelectrolyte solutions were transferred to 100-mL volumetric flasks along with 10 mL of a 200 mg/L (h0.2mg) ponceau S dye solution and 4 mL of 0.5 mol/L H2S04. The flasks were filled to volume with the appropriate solvent and mixed. The contents of the flasks were transferred to 250-mL separatory funnels, 20 mL of freon (C2C13F3) was added, and the funnels were shaken 100 times. The phases were allowed to separate for 15 min. The hydrophobic precipitate is insoluble in water and freon, and adheres to the freon/water interface. On settling, the precipitate gathers rapidly between the two phases. The absorbance of the aqueous phase was read in 1-cm cells on a spectrophotometer at 520 nm. Plots of absorbance vs. milliequivalenta of polyelectrolyte yielded plots with negative slopes. Samples of unknown concentration are run in the same manner. Equation 1is used to calculate concentrations
mequiv of charged N (aA/slope) liter vol of sample (liters)
(1)
where AA equals the change in absorbance. Concentrations expressed in mass units, mg/L, may be calculated from the results of eq l,by dividing by the polymer charge density in mequiv/mg. In this analysis the sample volume may be varied, depending on the concentration, to give reasonable absorbance readings. 0 1987 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 59, NO. 10, MAY 15, 1987
-5
Oqk
2
'
O9\
08
i1
07-
8
-
6
OL
0O 67 I
05041
04-
0302
1445
03t 02
-
-
\ I
\
01
0
1
2
3
4
5 6 7 8 meq charged Nitrcgsn (x103)
9
10
11
0
12
"I
I
"s
01
0
1
2
3
4
5
6
7
8
2
3
4
5
rrmc charged Nitrcgen (xlo')
Figure 1. Absorbance values vs. mequk of DMAIEPI in dlstilled and reconstituted Mississippi River water.
02
1
9
10
11
12
meq charged Nitrogen(x103)
Figure 2. Absorbance values vs. mequiv of DMDAAC in distilled and reconstituted Mississippi River water.
Volumes of up to 86 mL may be used for dilute polyelectrolyte samples.
RESULTS AND DISCUSSION A problem associated with dye complexation procedures for polyelectrolytes has been the tendency of the insoluble complex to remain in suspension in colloidal form. This contributes to the total light absorbance as turbidity, which, unless removed, will cause considerable error in the procedure. Filtration is slow and there is usually an uncorrected amount of dye lost to the filtering medium. Dey and Palit effectively used centrifugation to remove the precipitate, but this is time-consuming and requires another major piece of equipment. This step was eliminated by taking advantage of the natural hydrophobicity of the insoluble polycation-dye complex. Shaking the test mixture with a small volume of water-insoluble solvent (Freon) causes the colloidal suspension to agglomerate and settle rapidly to the interface as a strong weblike structure. Once this interference is removed, the analysis is straightforward. Other dyes were examined in addition to ponceau S. These acid were Eriochrome Black T, anthraquionone-l,5-disulfonic disodium salt, eosin B, and alizarine sodium monosulfate. These dyes either were too pH sensitive or complexed readily with calcium ion or did both. These difficulties were not evident with ponceau S using the described procedure. The calibration curves for poly(DMDAAC) and DMA/EPI compounds are shown in Figures 1 and 2. The curves were
Figure 3. Effect of excess DMAIEPI on absorbance values in distilled
water. constructed by using both distilled water and reconstituted Mississippi River water in order to represent a natural water source. These curves do show a matrix effect which, while slight, is real. For optimum results, a calibration curve must be constructed using a solvent approximating that of the water sample being analyzed. With proper sample size selection, this method is sensitive mequiv/L (or for the polycations exdown to (3-4) X amined here, 0.5-1.0 mg/L). Figure 3 shows that there is also an upper limit restriction. When the polyelectrolyte is in excess, it will resolubilize, or restabilize, the colloidal precipitate, which causes the absorbance readings to increase with increasing polycation concentration. This procedure has been found especially useful in adsorption studies for the two polyelectrolytes discussed, as well as in the determination of their Mark-Houwink-Sakarada constants (16, 17). Registry No. H20,7732-18-5; ponceau S, 6226-79-5; poIyDMDAAC, 78130-34-4;(DMA)(EPI) (copolymer),25988-97-0.
LITERATURE CITED Evisifeev, M. M.; Sadimenko, L. P.; Sokolov, V. P.; Samenov, A. D.; Bagdasarov, K. N.; Lokshina, G. A. I z v . Sev.-Kavk. Nauchn. Tsentra Vyssh. Shk., Estestv. Nauki1982, 16, 5 5 . Wee, V. T. Water Res. 1984, 18 (2), 223. Pilipenko, A. T.; Pshinko, G. N.; Zhebentyaev, A. I.; Volkova, A. I.; Denlsenko, V. P. Khlm. Tekhnol. Vody 1980, 2 (2), 130. Chrlstopoulos, T. K.; Diamandis. E. P.; Hadjiloannou, T. P. Anal. Chim. Acta 1982, 143, 143. Tsubouchi, M.; Mltsushio, H.; Yamasaki, N. Anal. Chem. 1981, 5 3 , 1957. Nakashima, R.; Sasaki, S.; Shibata, S. Nagoya Kogyo Gptsu Shikensho Hokoku 1973, 22 ( 5 ) , 183. Kawase, J.; Yamanaka, M. Analyst (London) 1979, 104, 750. Wang, L. K.; Langley, D. F. Arch. Environ. Contam. Toxicol. 1977, 5 , 447. Wang, L. K. U.S. Patent 3992149 (Nov. 16, 1976) Chem. Abstr. 1977, 8 6 , 110878. Kawase, J. Anal. Chem. 1980, 5 2 , 2124. Wang, L. K.; Shuster, W. W. Ind. Eng. Chem., Rod. Res. Dev. 1975, 14, 312. Josephs. R.; Feltelson, J. J . folym. Sci., folym. Chem. Ed. 1983, 1 , 3385. Toei, K.; ZaAzu, T. Anal. Chim. Acta 1985, 174, 369. Klyachko. Y. A.; Shnaider, M. A.; Kamenskaya, E. V.: Topchiev, D. A,; Korshunova, M. L. I z v . Vyssh. Uchebn. Zaved., Pishch. Tekhnol. 1984, 4 , 95. Dey, A. N.; Pallt, S. R. Indian J . Chem. 1988, 6 , 538. Burkhardt, C. W.; McCarthy. K. J.; Parazak, D. P. J . folym. Sci., f o lym. Lett., in press. McCarthy, K. J.; Burkhardt, C. W.; Parazak, D. P., submitted for publication In J . Appl. folym. Sci.
RECEIVED for review November 19,1986. Accepted February 18, 1987. The authors express their appreciation to the Petrolite Corporation for authorizing publication of this work.
