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Studies on the electrocapillary curves of anionic surfactants in presence of non-ionic surfactants
Tolunro, Vol
23, pp. 667469
Pergamon Press. 1976 Prmted m Great Bnmn
SHORT COMMUNICATIONS STUDIES ON THE ELECTROCAPILLARY CURVES OF ANIONIC SURFACTANTS IN PRESENCE OF NON-IONIC SURFACTANTS RAMFSH BEMFH, R. N. GOYAL and
Chemistry
Department,
(Received 1 October
University
1975. Remed
WAHID U. MALIK
of Roorkee,
India
19 January 1976. Accepted 21 January 1976)
Polarographic maxima of simple and complex metal ions have been effectively suppressed by the use of surfactantslm3. In most cases, catiomc soaps suppress the negative maxima while anionic soaps suppress the positive maxima.’ However no such simple relation has been found for non-ionic surfactants. Studies have shown that weak posittve charges may be associated with the micelles 01 polyoxyethyl non-iomc surfactants, but the sign of these charges is not definite. The changes in the electrocapillary curves of ionic surfactants on addition of non-ionic surfactants provide a means to assess the nature of the net effective charge on the latter (and hence their effectiveness in suppressing positive and/or negative polarographic max-
ima). Studies have, therefore, been carried out on the effect of four such non-ionic surfactants, viz. Tween 20, Tween 40, Nonidet P40, and Nonex 501 on the electrocapillary curves of three anionic surfactants, viz. Aerosol IB (di-isobutyl sodium sulphosuccinate, c.m.c. 0.20 M), Manaxol OT (dioctyl sodium sulphosuccinate, c.m.c. 6.8 x 10m4 M) and SLS (sodium lauryl sulphate, c.m.c. 8.2 x 10m3 M). EXPERIMENTAL The surfactants were B.D.H. products. Other reagents used were of analytical-reagent grade. All solutions were prepared in doubly-distilled water
0 -02
Potential,
Roorkee,
V
-04
-Cl6 -08
Potefrtial,
-10
-1.2
-14
V
NONIDET WO
301
Potential, Fig.
1. Electrocaptllary
V
curves m 0.12 M Aerosol 0.08 g/100 ml concentrations 667
0 -02 -0.4 -fJ6 -08 -1.0 -I.2 -1.4 Potential, V
IB m the presence of A 0.0, B 0.01, of non-ionic surfactants.
C 0.04, D
668
SHORT
Table 1. Potentials Manaxol OT and
COMMUNICATIONS
at the electrocapillary maxrma m the presence of Aerosol IB. SLS alone and along with varymg amounts of the non-tome surfactants Potential
Concentration of the non-iomc surfactant, g/l00 ml 0.0 Tween 20 0.01 004 0.08 Tween 40 0.01 0.04 0.08 Nonidet P40 0.0 1 0.04 008 Nonex 501 001 0.04 008
Aerosol
AhD
Manaxol
OT
SLS
- 0.40
- 0.54
- 0.64
-0.30 -0 18 -0.12
-0.42 -0.30 - 0.20
-056 - 0.48 -0.30
-0.34 -0.30 -0.20
-0.48 - 0.40 -032
- 0.60 -0.52 - 0.44
-0.26 -0.16 -0.10
- 0.40 -030 -0 18
-0.54 - 0.42 -0.30
-0.22 -0.12 -0.08
-0.36 - 0.24 -0 18
-0.50 - ,040 - 0.24
A Cambrtdge pen-recordmg polarograph was used for electrocaptllary measurements The solutrons were deaerated by bubbling purtfied mtrogen through them m H-type polarographtc cells. At least 20 drops were counted and the drop-time was measured with a prectston stop-watch, each readmg bemg repeated at least three ttmes. The electrocapillary measurements were carrted out from 0.0 to - 1.4V at constant temperature (25 k I”). The concentratton of the amomc surfactants was kept below then respective c m c ‘s. RESLILTS
IB
at the electrocaprllary maxtmum. 1’
DISCUSSION
Polyoxyethyl non-romc surfactants may have cattomc character. Chwala and Martma have proposed the existence of anionic character for the ethylene oxide adducts. However, Wurzschmttt.’ who studted the analytrcal behaviour of ethylene oxtde adducts, concluded that in aqueous soluttons they are present as catromc polyoxomum compounds Wurzschmrtt assumes that only a few of the ether oxygen atoms form oxonium tons and thts fraction has been termed the degree of oxontum formatron. Hsiaoh and Scholler’ a have supported these vtews The present studies further confirm the extstence of catton-actrve characteristtcs m these non-romc surfactants. Typrcal electrocaprllary curves obtained by plottmg drop-trme against apphed potentral are deptcted in Ftg. I. These curves, although parabolic, are marked by a lack of symmetry, mdtcating adsorptton of the surfactant on the mercury-solutron Interface. Lrpmann’ has shown that mercury carrtes the postttve charge (when the applied potentral IS zero). as a result of whrch the mterfacial tension is decreased and a lower drop-time 1s observed. As the mercury IS polarized to more negatrve potentrals. the postttve charge decreases and at a certam potenttal it disappears. At thus pomt the mterfacial tension IS maximum and hence a maxrmum drop-ttme 1s recorded Further negative polarrzation results m a drop of interfactal tensron and hence lower drop-trmes. An exammatron of the electrocapdlary curves shows that the non-ionic surfactants. Tween 20. Tween 40, Nomdet P40 and Nonex 501 influence the electrocaptllary curve of the anionic surfactants Aerosol IB. Manaxol OT and SLS m more or less the same manner The curves are shtfted downwards and
towards more posttive potentials with mcreasmg concentratton of the non-ionic surfactant and they progresstvely lose theu symmetry The values of the electrocaprllary maxima m the presence of the vartous anionic surfactants used (Table 1) show that their adsorbability at the mercury-solution interface follows the order: SLS ) Manaxol OT ) Aerosol IB. The gradual shift m the electrocapillary maxrma towards more positive potentials on additton of the non-tonic surfactants Indicates neutrahzation of the adsorbed surfaceactrve agent by the added non-ionic surfactant and its subsequent adsorptton at the mercury-solutron Interface. The shift m electrocapillary maxima is then in the order. Aerosol IB - Manaxol OT ) SLS. Thus the least shaft occurs in the case of SLS whrch ts the most strongly adsorbed amomc surfactant. These data provtde evrdence that the micelles of the polyoxyethylated non-iomc surfactants are assocrated wrth a net posntve charge. The values of the electrocaprllary maxtma m presence of added non-rontc surfactants (Table 1) show that the shaft caused by these surfactants follows the order: Nonex 501 ) Nomdet P40 > Tween 20 ) Tween 40. Thus may well be the order of the magmtude of posttrve charge carrted by the mrcelles of these non-tome surfactants
REFERENCES
1. W. U. Maltk and P. Chand, Anal. Chmr., 1965. 37. 1592. 2. W U. Mahk and 0. P. Jhamb. J. AIM. 011 Chrm. Sot. 1972. 49. 170. 3. W U Malik. P Chand and S. M. Saleem, Taluntcr. 1968. 15. 133. 1937. 4. A. Chwala and A Martma. Mrllrrrrd Trztilhrr.. 18. 992 Z. Anal. Chrru., 1950. 130. 105 5. B. Wurzschmitt, 6. L Hsiao, H M. Dunmng and P. B. Lorenz. J. Ph~7.s Chern., 1956, 60. 657. 7. C. Scholler. Angrw. Chrm.. 1950, 7. 60. Rundschau, 1950, 5. 77. 8. I&m, Ted Ann. Chim. Phys. 1876, 15. 494, 1877. 9 G. Lippmann, 16. 265.
669
SHORT COMMUNICATIONS
Summary-Polyoxyethylated non-ionic surfactants such as Tween 20, Tween 40, Nonidet P40 and Nonex 501 have been supposed to be associated with cationic characteristics. Studies on the effect of these surfactants on the electrocapillary curves of the anionic surfactants Aerosol IB, Manaxol OT and sodium lauryl sulphate (SLS), show that the electrocapillary maxima shift towards positive potentials. The order of adsorption of the anionic surfactants is SLS ) Manaxol OT j Aerosol IB while OT j SLS which confirms association of the shift in maxima is m the order Aerosol IB - Manaxol cationic characteristics with the micelles of these non-ionic surfactants. The magnitude of the shift m electrocapillary maxima is Nonex 501 ) Nonidet P40) Tween 20 j Tween 40 which may be the order of magnitude of the positive charge carried by these non-ionic surfactants.
Tulanro. Vol 23.pp 669411 PergdmonPress, 1976Prmted m Great Bntam
EFFECTS OF AUXILIARY COMPLEX-FORMING AGENTS ON THE RATE OF METALLOCHROMIC INDICATOR COLOUR CHANGE-IV* MECHANISM OF THE COLOUR CHANGE OF XYLENOL ORANGE IN COPPER(IItEDTA TITRATIONS HIROKO
WADA,TOMOSUKE
Laboratory
of Analytical Gokiso-cho,
ISHIZUKI and
Chemistry, Showa-ku,
Nagoya Nagoya,
GENKICHI
NAKAGAWA
Institute of Technology, 466, Japan
(Recerved 12 March 1976. Accepted 18 March 1976)
In the copper(IItEDTA titration with Xylenol Orange (X0) as indicator, hexamine slows down the rate of colour change of X0. 1,2 In the work described here, the rate of the substitution reaction of the copper(IIkX0 chelate with EDTA was determined in MES buffer [2-(N-morpho1mo)ethanesulphonic acid] and in hexamine buffer, and the mechanism of the disturbing effect of hexamine on the colour change of the indicator discussed. EXPERIMENTAL
and purified in a manner similar to that in the literature.3 The free acid form (H,XO) was dissolved in water, and the solution stored in a refrigerator. Dissociation constants of X0 determined by spectrophotometry and pH-titration were in good agreement with the values given by Murakami et ~1.~ A copper(H) solution was prepared from the reagentgrade nitrate. Reagent-grade hexamme dried over phosphorus pentoxtde was used without further purification. The purity was established as 99.0% by means of pH-titration with sodium hydroxide in the presence of excess of hydrochloric acid. Other reagents and apparatus employed were the same as those reported previously.4 All experiments were carried out at 25 f I” and at ionic strength of 0.1 (KNO,). X0
with 0.198M sodium hydroxide shows the formation of Cu,HXOat pH 2, and further release of one proton, which corresponds to the sixth proton of H,XO, takes place in the pH-range from 3.5 to 5.5. In thts pH-range the absorption maximum shifts from 440 to 574nm, and an isosbestic point occurs at 487 nm. From these results the following equilibrium exists: Cu,XO*+ H+ $ Cu2HXO-. The equilibrium constant, K&x0 = [Cu,HXO-]/[Cn,XO*-][H’], was evaluated as lo4 ss by spectrophotometry and pH-titration.
was synthesized
06-
04s 5 f :: 9
RESULTS AND DISCUSSION
The composrtlon of copper(lltX0
chelates
From the results of the contmuous variation method, the molar-ratio method by spectrophotometry and the potentiometric titration wtth use of a copper(H) ion-selective electrode, the ratio of copper to X0 was essentially 2: 1 in MES buffer. The pH-titration of a solution 3.76 x 10e3M in Cu and 0.934 x 10m3M in H,XO * Part III: Talanta, 1976, 23, 155.
500
600
550 Wavelength,
nm
Fig. 1. Spectra of Cu-X0 chelates. Cc. 1.6 x 10m4!vf, Cxo 1.1 x lO-‘M. 1, X0 blank; 2, Cu,XO*-; 3, Cu,XOL*-, Chex 2.0 x lo-‘M, pH 6.0.
23, pp. 667469
Pergamon Press. 1976 Prmted m Great Bnmn
SHORT COMMUNICATIONS STUDIES ON THE ELECTROCAPILLARY CURVES OF ANIONIC SURFACTANTS IN PRESENCE OF NON-IONIC SURFACTANTS RAMFSH BEMFH, R. N. GOYAL and
Chemistry
Department,
(Received 1 October
University
1975. Remed
WAHID U. MALIK
of Roorkee,
India
19 January 1976. Accepted 21 January 1976)
Polarographic maxima of simple and complex metal ions have been effectively suppressed by the use of surfactantslm3. In most cases, catiomc soaps suppress the negative maxima while anionic soaps suppress the positive maxima.’ However no such simple relation has been found for non-ionic surfactants. Studies have shown that weak posittve charges may be associated with the micelles 01 polyoxyethyl non-iomc surfactants, but the sign of these charges is not definite. The changes in the electrocapillary curves of ionic surfactants on addition of non-ionic surfactants provide a means to assess the nature of the net effective charge on the latter (and hence their effectiveness in suppressing positive and/or negative polarographic max-
ima). Studies have, therefore, been carried out on the effect of four such non-ionic surfactants, viz. Tween 20, Tween 40, Nonidet P40, and Nonex 501 on the electrocapillary curves of three anionic surfactants, viz. Aerosol IB (di-isobutyl sodium sulphosuccinate, c.m.c. 0.20 M), Manaxol OT (dioctyl sodium sulphosuccinate, c.m.c. 6.8 x 10m4 M) and SLS (sodium lauryl sulphate, c.m.c. 8.2 x 10m3 M). EXPERIMENTAL The surfactants were B.D.H. products. Other reagents used were of analytical-reagent grade. All solutions were prepared in doubly-distilled water
0 -02
Potential,
Roorkee,
V
-04
-Cl6 -08
Potefrtial,
-10
-1.2
-14
V
NONIDET WO
301
Potential, Fig.
1. Electrocaptllary
V
curves m 0.12 M Aerosol 0.08 g/100 ml concentrations 667
0 -02 -0.4 -fJ6 -08 -1.0 -I.2 -1.4 Potential, V
IB m the presence of A 0.0, B 0.01, of non-ionic surfactants.
C 0.04, D
668
SHORT
Table 1. Potentials Manaxol OT and
COMMUNICATIONS
at the electrocapillary maxrma m the presence of Aerosol IB. SLS alone and along with varymg amounts of the non-tome surfactants Potential
Concentration of the non-iomc surfactant, g/l00 ml 0.0 Tween 20 0.01 004 0.08 Tween 40 0.01 0.04 0.08 Nonidet P40 0.0 1 0.04 008 Nonex 501 001 0.04 008
Aerosol
AhD
Manaxol
OT
SLS
- 0.40
- 0.54
- 0.64
-0.30 -0 18 -0.12
-0.42 -0.30 - 0.20
-056 - 0.48 -0.30
-0.34 -0.30 -0.20
-0.48 - 0.40 -032
- 0.60 -0.52 - 0.44
-0.26 -0.16 -0.10
- 0.40 -030 -0 18
-0.54 - 0.42 -0.30
-0.22 -0.12 -0.08
-0.36 - 0.24 -0 18
-0.50 - ,040 - 0.24
A Cambrtdge pen-recordmg polarograph was used for electrocaptllary measurements The solutrons were deaerated by bubbling purtfied mtrogen through them m H-type polarographtc cells. At least 20 drops were counted and the drop-time was measured with a prectston stop-watch, each readmg bemg repeated at least three ttmes. The electrocapillary measurements were carrted out from 0.0 to - 1.4V at constant temperature (25 k I”). The concentratton of the amomc surfactants was kept below then respective c m c ‘s. RESLILTS
IB
at the electrocaprllary maxtmum. 1’
DISCUSSION
Polyoxyethyl non-romc surfactants may have cattomc character. Chwala and Martma have proposed the existence of anionic character for the ethylene oxide adducts. However, Wurzschmttt.’ who studted the analytrcal behaviour of ethylene oxtde adducts, concluded that in aqueous soluttons they are present as catromc polyoxomum compounds Wurzschmrtt assumes that only a few of the ether oxygen atoms form oxonium tons and thts fraction has been termed the degree of oxontum formatron. Hsiaoh and Scholler’ a have supported these vtews The present studies further confirm the extstence of catton-actrve characteristtcs m these non-romc surfactants. Typrcal electrocaprllary curves obtained by plottmg drop-trme against apphed potentral are deptcted in Ftg. I. These curves, although parabolic, are marked by a lack of symmetry, mdtcating adsorptton of the surfactant on the mercury-solutron Interface. Lrpmann’ has shown that mercury carrtes the postttve charge (when the applied potentral IS zero). as a result of whrch the mterfacial tension is decreased and a lower drop-time 1s observed. As the mercury IS polarized to more negatrve potentrals. the postttve charge decreases and at a certam potenttal it disappears. At thus pomt the mterfacial tension IS maximum and hence a maxrmum drop-ttme 1s recorded Further negative polarrzation results m a drop of interfactal tensron and hence lower drop-trmes. An exammatron of the electrocapdlary curves shows that the non-ionic surfactants. Tween 20. Tween 40, Nomdet P40 and Nonex 501 influence the electrocaptllary curve of the anionic surfactants Aerosol IB. Manaxol OT and SLS m more or less the same manner The curves are shtfted downwards and
towards more posttive potentials with mcreasmg concentratton of the non-ionic surfactant and they progresstvely lose theu symmetry The values of the electrocaprllary maxima m the presence of the vartous anionic surfactants used (Table 1) show that their adsorbability at the mercury-solution interface follows the order: SLS ) Manaxol OT ) Aerosol IB. The gradual shift m the electrocapillary maxrma towards more positive potentials on additton of the non-tonic surfactants Indicates neutrahzation of the adsorbed surfaceactrve agent by the added non-ionic surfactant and its subsequent adsorptton at the mercury-solutron Interface. The shift m electrocapillary maxima is then in the order. Aerosol IB - Manaxol OT ) SLS. Thus the least shaft occurs in the case of SLS whrch ts the most strongly adsorbed amomc surfactant. These data provtde evrdence that the micelles of the polyoxyethylated non-iomc surfactants are assocrated wrth a net posntve charge. The values of the electrocaprllary maxtma m presence of added non-rontc surfactants (Table 1) show that the shaft caused by these surfactants follows the order: Nonex 501 ) Nomdet P40 > Tween 20 ) Tween 40. Thus may well be the order of the magmtude of posttrve charge carrted by the mrcelles of these non-tome surfactants
REFERENCES
1. W. U. Maltk and P. Chand, Anal. Chmr., 1965. 37. 1592. 2. W U. Mahk and 0. P. Jhamb. J. AIM. 011 Chrm. Sot. 1972. 49. 170. 3. W U Malik. P Chand and S. M. Saleem, Taluntcr. 1968. 15. 133. 1937. 4. A. Chwala and A Martma. Mrllrrrrd Trztilhrr.. 18. 992 Z. Anal. Chrru., 1950. 130. 105 5. B. Wurzschmitt, 6. L Hsiao, H M. Dunmng and P. B. Lorenz. J. Ph~7.s Chern., 1956, 60. 657. 7. C. Scholler. Angrw. Chrm.. 1950, 7. 60. Rundschau, 1950, 5. 77. 8. I&m, Ted Ann. Chim. Phys. 1876, 15. 494, 1877. 9 G. Lippmann, 16. 265.
669
SHORT COMMUNICATIONS
Summary-Polyoxyethylated non-ionic surfactants such as Tween 20, Tween 40, Nonidet P40 and Nonex 501 have been supposed to be associated with cationic characteristics. Studies on the effect of these surfactants on the electrocapillary curves of the anionic surfactants Aerosol IB, Manaxol OT and sodium lauryl sulphate (SLS), show that the electrocapillary maxima shift towards positive potentials. The order of adsorption of the anionic surfactants is SLS ) Manaxol OT j Aerosol IB while OT j SLS which confirms association of the shift in maxima is m the order Aerosol IB - Manaxol cationic characteristics with the micelles of these non-ionic surfactants. The magnitude of the shift m electrocapillary maxima is Nonex 501 ) Nonidet P40) Tween 20 j Tween 40 which may be the order of magnitude of the positive charge carried by these non-ionic surfactants.
Tulanro. Vol 23.pp 669411 PergdmonPress, 1976Prmted m Great Bntam
EFFECTS OF AUXILIARY COMPLEX-FORMING AGENTS ON THE RATE OF METALLOCHROMIC INDICATOR COLOUR CHANGE-IV* MECHANISM OF THE COLOUR CHANGE OF XYLENOL ORANGE IN COPPER(IItEDTA TITRATIONS HIROKO
WADA,TOMOSUKE
Laboratory
of Analytical Gokiso-cho,
ISHIZUKI and
Chemistry, Showa-ku,
Nagoya Nagoya,
GENKICHI
NAKAGAWA
Institute of Technology, 466, Japan
(Recerved 12 March 1976. Accepted 18 March 1976)
In the copper(IItEDTA titration with Xylenol Orange (X0) as indicator, hexamine slows down the rate of colour change of X0. 1,2 In the work described here, the rate of the substitution reaction of the copper(IIkX0 chelate with EDTA was determined in MES buffer [2-(N-morpho1mo)ethanesulphonic acid] and in hexamine buffer, and the mechanism of the disturbing effect of hexamine on the colour change of the indicator discussed. EXPERIMENTAL
and purified in a manner similar to that in the literature.3 The free acid form (H,XO) was dissolved in water, and the solution stored in a refrigerator. Dissociation constants of X0 determined by spectrophotometry and pH-titration were in good agreement with the values given by Murakami et ~1.~ A copper(H) solution was prepared from the reagentgrade nitrate. Reagent-grade hexamme dried over phosphorus pentoxtde was used without further purification. The purity was established as 99.0% by means of pH-titration with sodium hydroxide in the presence of excess of hydrochloric acid. Other reagents and apparatus employed were the same as those reported previously.4 All experiments were carried out at 25 f I” and at ionic strength of 0.1 (KNO,). X0
with 0.198M sodium hydroxide shows the formation of Cu,HXOat pH 2, and further release of one proton, which corresponds to the sixth proton of H,XO, takes place in the pH-range from 3.5 to 5.5. In thts pH-range the absorption maximum shifts from 440 to 574nm, and an isosbestic point occurs at 487 nm. From these results the following equilibrium exists: Cu,XO*+ H+ $ Cu2HXO-. The equilibrium constant, K&x0 = [Cu,HXO-]/[Cn,XO*-][H’], was evaluated as lo4 ss by spectrophotometry and pH-titration.
was synthesized
06-
04s 5 f :: 9
RESULTS AND DISCUSSION
The composrtlon of copper(lltX0
chelates
From the results of the contmuous variation method, the molar-ratio method by spectrophotometry and the potentiometric titration wtth use of a copper(H) ion-selective electrode, the ratio of copper to X0 was essentially 2: 1 in MES buffer. The pH-titration of a solution 3.76 x 10e3M in Cu and 0.934 x 10m3M in H,XO * Part III: Talanta, 1976, 23, 155.
500
600
550 Wavelength,
nm
Fig. 1. Spectra of Cu-X0 chelates. Cc. 1.6 x 10m4!vf, Cxo 1.1 x lO-‘M. 1, X0 blank; 2, Cu,XO*-; 3, Cu,XOL*-, Chex 2.0 x lo-‘M, pH 6.0.