ANALYTICAL CHEMISTRY, VOL. 51, NO. 7, JUNE 1979 (8) W. A. Aue and S. Kapila, J . Chromatogr. Sci., 11, 255 (1973) (9) M. A. Biondi, M. H. Bortner, and T. Baurer, Ed., "Defense Nuclear Agency Reaction Rate Handbook", March 1975, 4th rev., Chap. 12. (10) S. G. Lias and P. Ausloos, "Ion Molecule Reactions", American Chemical Society, Washington, D.C., 1975, Chap. 4. (11) F. C. Fehsenfeld, P. J. Crutzen, A. L. Schmeltekopf, C. J. Howard, D. L. Albrtton, E. E. Ferguson, J. A. Davidson, and H. I . Schiff, J . Geophys Res., 8 1 , 4454 (1976). ( 12) F. C. Fehsenfeld, NOAA Environmental Research Laboratories, Boulder, Colo., personal communication, Sept. 1978. (13) J . Phys. Chem. Ref. Data, 6(1), 748, 757 (1977). (14) W. E . Wentworth, R. George, and H.Keith, J . Chem. Phys., 5 1 , 1791 (1969), references cited therein. (15) A . J. Gordon and R . A . Ford, "The Chemists Companion", John Wiley and Sons, New York. 1972.
859
(16) S W Benson. J . Chem. Educ.. 4 2 , 502 (1965). (17) 8.Darwent, Natl. Stand. Ref. Data Ser., Natl. Bur. Stand., No. 31 (1971). (18) "Handbook of Chemistry and Physics", 56th ed., The Chemical Rubber Company, Cleveland, Ohio, 1976. (19) W . E. Wentworth, R . S.Becker, and R. Tung, J . Phys. [?hem., 47, 1652 (1967), references cited therein.
RECEIVED for review October 19, 1978. Accepted February 23, 1979. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, to Research Corporation, and to the National Science Foundation for support of this research.
Nylon Membrane Electrode Selective for High Molecular Weight Alkyl Aryl Sulfonates Steven H. Hoke,* A. Gene Collins, and C. A. Reynolds' Bartlesville Energy Technology Center, U.S. Department of Energy, P. 0. Box 1398, Bartlesville, Oklahoma 74003
A nylon membrane electrode selective for pentadecyl benzene sulfonate is described. The active material in the membrane is a quaternary ammonium sulfonate salt. The electrode gives Nernstlan response to pentadecyl benzene sulfonate from the critical micelle concentration down to lo-' M. Selectivity coefficients for several sulfonates and inorganic anions are given. The electrode has been used as an end-point indicator for the potentiometric titration of sulfonates. The results from this method and the Methylene Blue Method for several petroleum sulfonates compare favorably.
Since the 1930's, petroleum sulfonates have found numerous applications for their surface-active properties. The hundreds of millions of pounds produced annually (1) will eventually require constant environmental monitoring. Surfactant flooding using petroleum sulfonates is becoming increasingly popular for tertiary oil recovery. Although environmental problems are not likely with sulfonates for oil recovery, monitoring the flow of surfactant through the underground reservoir is essential. Modifications of the two-phase Epton titration are the most widely used methods for determining sulfonates (2, 3). This titration procedure has been improved using various dyes and titrants ( 4 , 5 ) . Colorimeters improve the sensitivity over visual end-point detection ( 5 , 6). However, the two-phase titration consumes much time, and colored samples affect the accuracy. Ion selective electrodes offer a n attractive alternative for sulfonate analysis. Most of the sulfonate electrodes reported are of t h e liquid-membrane type. Coetzee and Freiser ( 7 ) prepared t h e methyltricaprylyl ammonium salt of several organic and inorganic anions using 1-decanol as t h e liquid phase. T h e electrode for p-toluene sulfonate gave a slope of 57 mV/log over t h e linear range between lo-' and M. Frieser e t al. (8) later coated a Pt wire by dipping it into a PVC solution containing the same complex. This electrode extended the linear response to p-toluene sulfonate down to 2.5 X M. A similar electrode for 1-naphthalene sulfonate Present address, Chemistry Department, University of Kansas, L a w r e n c e , K a n s a s 66045.
produced linear response only down to M (9). Nernstian response to dodecylbenzene sulfonate (DBS-) down to M was reported by Gavach and Bertrand (10) using a n ammonium complex of DBS- in a liquid membrane of nitrobenzene. Ishibashi et al. (11) reported a 1,2-dichloroethane membrane containing the Crystal Violet complex of DBS-. Near-Nernstian response was observed down to M sulfonate. Ferroin complexes of DBS- were reported for liquid membranes by Ciocan and Anghel (12),in PVC matrix-type electrodes (131, and in a porous graphite membrane (14). No apparent difference in response between these three electrodes was observed. Anghel and Ciocan (15) later reported a similar liquid electrode, except that ferroin was replaced with bis(dimethylglyoxime)(o-phenanthroline)cobaltate(III). However, no change in electrode response was indicated. Most sulfonate electrodes reported are the liquid-membrane type which are difficult to construct and involve the manipulation of organic solvents. It would be desirable to have a n electrode which is easy to construct and gives Nernstian response to sulfonates over a wider concentration range. Higuchi (16, 17) reported a nylon electrode which responded to organic anions. Our laboratory found this electrode gives 30-40 mV/decade response to sulfonate ions. Since plastic electrodes are more desirable to work with than the liquidmembrane type, the authors decided to incorporate various quaternary ammonium sulfonate complexes into the nylon matrix to enhance its response.
EXPERIMENTAL Apparatus. Electrode potentials were measured with an Orion 801A Ionalyzer and recorded on a Perkin-Elmer model 56 recorder. A model E536 Brinkmann automatic titrator was used for all
titrations. Materials. The following chemicals were generously donated by their suppliers: Hyamine 1622 (see structure below), and
H Y A M I N E 1622 (DIISCBUTYLPHENCXYETHCXYETHYL DIMETHYL BENZYL A M M O N I U M CHLORIDE MCNCHI'DRATE)
This article not subject to U.S. Copyright. Published 1979 by the American Chemical Society
860
ANALYTICAL CHEMISTRY, VOL. 51, NO. 7, JUNE 1979
Table I.
Determination of Commercial Sulfonates 70 by wt.
sulfonate
eyuiv wt
titration
supplier
Methylene Blue
Cities Service AA-10
348.5
96.0
92.0
Conoco Blend
408
96.1 96.0 33.6 33.6
Flood Aid 1 4 1
450
48.6
45.0
Llorco H-62
520
47.3 63.1
62.0
P l a s t i c t u be
32.5 A g 1 Ag C I
45.5 OWN K C I
65.3
Kasul-SS Synex 1152
482.5
Shell H M b
540
Shell Regular
465
Stepaii Petro Step Sulfonate Stepan Petro Step PDBS Witco Petronate TRS-18 R'itco Petronate TRS-10-41 0 Witco Petronate TRS-12
450 390.5 495 422 410
37.6 40.5 41.1 72.2 68.4 63.7
62.8 59.8 57.8 75.0 69.5 63.1 62.1 63.0 64.0 63.4
50
68
Nylon
61.6
Figure 1. Nylon membrane electrode and measuring circuit
75.1
Titrant. The titrant chosen for these analyses was Hyamine 1622. This quaternary ammonium salt was stable in water and precipitated well with the sulfonates tested. A 0.02 M solution of H yamine was standardized against LAS and pentadecyl benzene sulfonate.
62.5 59.6 75.0
RESULTS AND DISCUSSIONS
62.0 62.0
61.6
62.0
nonylphenol, Rohm and Haas; Elvamid 8064 nylon resin, Du Pont: dodecylbenzene sulfonate, Cities Service; pentadecylbenzene sulfonate, Stepan Chemical Company; and LAS Standard (linear alkyl benzene sulfonate),U.S. Environmental Protection Agency. Petroleum sulfonates are listed with their respective suppliers in Table I. Purification of Pentadecylbenzene Sulfonate. Twenty-five g of the sulfonate-oil-salt-water mixture was dissolved in 300 mL of CHC13. Upon standing overnight, the mixture was filtered through a fine 6.35-cm diameter sintered glass filter to remove the salt. The oil was removed by passing the chloroform solution through a column containing 100 g of 62-mesh silica. The column was then treated with 200 mL CHC1,. The sulfonate was reclaimed from the silica with 200 mL of methanol. After removing the solvent, the light yellow solid product (sulfonate) was stored in a desiccator. P r e p a r a t i o n of Complex. Ten mL of 0.1 M Hyamine 1622 was slowly added with stirring to 10 mL of 0.1 M sulfonate. The resulting white flocculant precipitate was allowed t o stand for 0.5 h before decanting. The precipitate was dissolved in hexane and centrifuged. Upon evaporation of the organic layer, a greenish yellow semisolid resulted which was stored in a desiccator. Nylon Solution. To 1 g of nylon pellets enough nonylphenol plasticizer and complex were added to make the final membrane composition 35% plasticizer and 2 % complex salt. This mixture was dissolved with 5 mL of methylenedichloride and 5 mL of methanol. Electrode Construction. The electrode body consisted of a 10-mL disposable pipet with the conical tip cut off to give an i.d. of 1-2 mm. The tip of the tube was dipped into a nylon solution coating the end to a height of 1 cm and forming a film over the end of the tube. After drying 3-4 min, the tip was touched to the surface of the nylon solution. This process was repeated four times allowing 3-4 min each time for drying. After the electrode dried overnight, 0.1 N KC1 was added to the inside of the tube and the outer membrane was soaked overnight in a dilute (ca. M) solution of the sulfonate ion to be measured. Potential Measurements. Electrodes were removed from the soaking solution, rinsed with deionized water, and placed in 100 mL of deionized water with a saturated calomel electrode as a reference. The solution was stirred at a constant rate and the potential was recorded with time. Upon reaching a stable potential (h0.5 mV/min), successive additions of sulfonate were made with the potential recorded after each addition.
Slope D e t e r m i n a t i o n . A detailed description of the electrode and measuring circuit is shown in Figure 1. T h e electrochemical cell can be represented by: Ag/AgCl/O. 1 N K C l / m e m brane / /sulfonate / S C E solution Figure 2 shows typical electrode response upon successive additions of sulfonate. Additions above the CMC (critical micelle concentration) cause a n increase in sulfonate ion activity which immediately decreases as micelles begin t o form. The slope of the electrode was obtained by plotting mV vs.-log [sulfonate] as indicated in Figure 3. T h e reduction in response a t high concentration was undoubtedly due to micelle formation of the sulfonate ions. At low concentration, response was slow- about lC-15 min. Slopes typically ranged between 55 and 59 mV/decade. Several electrodes were tested over a period of time and found to be functioning properly after 5 months. Electrodes prepared with the quaternary ammonium dodecylbenzene sulfonate complex only performed for 2-3 weeks. Presumably, this complex is more soluble in water and consequently leaches out of the membrane. Selectivity Determination. Several inorganic and organic anions were considered as possible interferences. Interference experiments were carried out by first measuring the electrode potential t o a lo4 M) solution containing the sulfonate ion the electrode was designed t o measure. T h e equilibrium mV reading was recorded, the electrodes were blotted dry and immersed in a sulfonate solution of identical concentration containing an interfering ion. By knowing the concentrations of the species in each solution, the electrode potentials, and the slope of the electrode, the following equation can be used t o calculate the selectivity coefficient of the interfering ion:
where aA = concentration of the ion measured, aB = concentration of interfering ion B, ZA = charge on ion A, and& = charge on ion B. As shown on Table 11, , high-molecular-weight sulfonates offer significant interference. Response of the electrode above p H 9 falls off rapidly; therefore, carboxylate interference could not be evaluated. T i t r a t i o n R e s u l t s . Since the electrode does respond t o a variety of sulfonates, it was decided t o use the sulfonate electrode as an end-point detector for titrating petroleum
ANALYTICAL CHEMISTRY,
VOL. 51, NO. 7,
JUNE
1979
861
1
140-
- 50-
120-
2 1000
> J J
-
I
80
-
601-
40 -
-200 7
5
6
- Lop
4
[PSI
Figure 3. Response of sulfonate electrode to pentadecyl benzene sulfonate. Slope over linear range, -57 mV/decade
20 -
---I 0
I J . ,
1
4
8
1
1 12
1
j I6
I
I 20
1
1 24 400k
interferent dodecylbenzene sulfonate methyldodecyl benzene sulfonate butyldodecyl benzene sulfonate octadecyl benzene sulfonate benzene sulfonate octylsulfate chloride sulfate
selectivity coefficient 0.18 0.15
1.36 9.6 3.0 x 1.4 x 10-3 5.7 x 1 0 - j 6.9 x 10.'
sulfonates. In most cases, good potentiometric breaks were obtained a t the end point (Figure 4). This electrode was expected to be an exceptionally good end-point detector because it responds not only to the decrease in sulfonate ion, but also exhibits near-Nernstian response to Hyamine concentration. Table I lists the results obtained for several commercial sulfonates analyzed by this method. Also listed are results obtained by the two-phase Epton titration or Methylene Blue Method, and by the supplier. Suppliers contacted also used the Methylene Blue Method. Results from the potentiometric titration method were obtained a t approximately equiv/L of sulfonate. Close agreement was found in almost all cases. T h e main advantages of the potentiometric titration method are that it is rapid, requiring approximately 10 min/run and the accuracy is fairly independent of the ability of the technician. The Methylene Blue Method involves the manipulation of organic chemicals and
J
l
7 200
++ - + - o
3 MILLILITERS
Potentiometric titration of 40 rnL of 2.5 benzene sulfonate with 0.0193 M Hyamine Figure 4.
X
M pentadecyl
Table HI. Effect of Sodium Chloride on Percent Recovery of a 40-mL Sample of Pentadecyl Benzene Sulfonate moles of PS 2.78
X
2.78 x
2.78
X
2.78 x 2.78 X
NaC1, moles/L
m L of
... 0.00125 0.00375 0.0100
3.33
100.0
3.26 3.22
100.9 96.1 108.1 113.2
0.0500
titrant
3.60 3.77
recovery, 70
is time-consuming, requiring the phases to separate between each increment of titrant. The color of'the sample also affects the accuracy of the end point. We have found that it takes
862
ANALYTICAL CHEMISTRY, VOL. 51, NO. 7, JUNE 1979
an experienced technician to obtain reliable results using the Methylene Blue Method. The results from Table I11 indicate that chloride ion may be included as part of the precipitate, leading to a positive error. Chloride has also been reported to give a positive error with the Methylene Blue Method ( 4 , 18). The interference of chloride on the results of surfactant analyses using quaternary ammonium salts needs further investigation.
ACKNOWLEDGMENT T h e authors thank M. W. Listen for testing many of the electrodes and C. A. Pearson for the Methylene Blue data.
LITERATURE CITED (1) C. Bluestein and B. R . Bluestein, "Anionic Surfactants", W. M. Linfield, Ed., Marcel Dekker, New York, 1976, Part 11, Chapter 9. (2) S.R. Epton, Trans. Faraday Soc., 44, 226 (1948). (3) L. Smith, E. W. Malmberg, H. W. Kelley, and S. Fowler, "The Quantitative Analysis of Adsorbed Petroleum Sulfonates", Paper SPE 5369 presented at the 45th Annual Regional Meeting of the Society of Petroleum Engineers of AIME, Ventura, Calif., April 1975. (4) G. F. Longman, "The Analysis of Detergents and Detergent Products", John Wiley 8 Sons, New York, 1977, pp 215-251.
(5) L. K . Wang and D. F. Langley, N . f n g i . Water Works Assoc., 89, 301, (1975). (6) "Standard Methods for the Examination of Water and Waste-Water", 14th ed., American Public Health Association, American Water Works Association, and Water Pollution Control Federation, Washington, D.C., 1976, pp 600-603. (7) C.J. Coetzee and H. Freiser, Anal. Cbem., 40, 2071 (1968); 41, 1129 (1969). (8) T. Fujinaga, S. Okazaki, and H. Freiser, Anal. Cbem., 46, 1842 (1974). (9) N. Ishibashi, A. Jyo, and K. Matsumoto, Chern. Lett., 1297 (1973). (10) C. Gavach and C. Bertrand, Anal. Chlrn. Acta, 55, 385, (1971). (11) N. Ishibashi, H. Kohara, and K. Horinouchi, Talents, 20, 867 (1973). (12) N. Ciocan and D. F. Anghel, Anal. Lett., 0, 705 (1976). (13) T. Tanaka, K. Hiiro, and A. Kawahara, Anal. Lett., 7 , 173, (1974). (14) N. Clocan and D. Anghel, Tenside Deterg., 13, 188, (1976). (15) D. F. Anghel and N. Ciocan, Anal. Lett., 10, 423, (1977). (16) T. Higuchi, C. R. Man, and J. L. Tossounian, Anal. Chem., 42, 1874, (1970). (17) T. Higuchi, U.S. Patent 3843505 (1974). (18) "Methods for Chemical Anatysis of Water and Waste", U S . Environmental Protection Agency, EPA-62546-74-003, Washington, D. C., 1974, p 157.
RECEIVED for review December 15, 1978. Accepted February 15, 1979. Mention of brand names does not imply endorsement by DOE.
Ion-Exchange Selectivity and Metal Ion Separations with a Perfluorinated Cation-Exchange Polymer H. L. Yeager" and A. Steck Department of Chemistry, The University of Calgary, Calgary, Alberta T2N 1N4, Canada
Selectivity coefficients for hydrogen Ion exchange with the alkali metal ions and silver ion have been measured for varying ionic fractions of metal ion using Nafion 120 perfluorinated sulfonate cation-exchange membrane. Powdered samples of Naflon were used to separate the alkali metal ions and alkaline earth ions by column chromatography. Results indicate that Nafion exhibits higher selectivity and more uniform exchange site environment than conventional sulfonate ion-exchange resins. The ion-exchange properties of Nafion are discussed in terms of its water sorption and morphology.
Homogeneous ion-exchange membranes have found application as separators in electrolysis ( 1 , 2 ) and battery cells ( 3 , 4 ) ,as analytical preconcentrating devices of various types (5-8), and as the essential component in industrial processes such as the production of chlorine-caustic (9). A study of the use of ion-exchange membranes in the electrolytic separation of ions has recently been published (10). Nafion (Du Pont and Co.) perfluorinated sulfonic acid ion-exchange membrane has been used in each of these applications because of its excellent chemical and thermal stability and good ionic transport properties. This material differs from conventional cross-linked polystyrene sulfonate resins in two important respects: Nafion is presumably not cross-linked, although the polymer is insoluble because of its very high molecular weight, and the ion-exchange capacity of Nafion is about four times smaller than typical sulfonate resins. The morphology of Nafion and its polymeric precursor have been studied by a variety of techniques (11-13); the results of these studies indicate that sulfonate exchange sites, exchangeable count0003-2700/79/0351-0862$01 .OO/O
erions, and sorbed water exist in ion clusters distributed throughout the polymer. The Bragg spacing distance of these clusters, determined by low angle X-ray scattering measurements, is about 50 8, ( 1 1 , 13). Recently the results of theoretical modeling and studies of some spectroscopic and transport properties of Nafion have been reported (14-1 7). We have studied ionic exchange rates, water uptake, and cation diffusion in Nafion for membranes equilibrated with water and other solvents (18,19). Diffusion of Na+ and Cs+ was found to be much higher in protic solvents than aprotic ones. In addition, the material demonstrated a high selectivity of Cs+ to Na+ in water and methanol solvents. We report here the results of the ion-exchange behavior of Nafion with regard to alkali metal ions and hydrogen ion. Chromatographic separations of alkali metal ions and of alkaline earth ions are also reported. The objectives of this research are to gain a better understanding of ion clustering through its influence on ion-exchange reactions, and to characterize the ionic selectivity of Nafion for membrane-related and other applications.
EXPERIMENTAL Materials. Nafion-120 (Plastics Dept., Du Pont and Co., Wilmington, Del. 19898) with nominal capacity and thickness of 0.83 mequiv/g dry H-form polymer and 0.025 cm, respectively, was used in this work. Reagent grade alkali metal chloride salts and silver nitrate were used as received. The radioisotopes '*Na and 13'Cs were obtained as carrier-free aqueous solutions from commercial sources. Procedure. Membrane samples of about 4 cm2 in area were pretreated by initial washing in 95% ethanol followed by repeated equilibrations in 1 M NaOH, water, 1 M HCl, and water. The pieces were then used in either the H-form or in a salt form obtained by soaking in the appropriate 0.1 M chloride salt solution, C 1979 American Chemical Society
