Estimation of non-ionic, surface-active substances in aqueous solutions by means of the Controlled Growth Mercury Electrode

In this paper, a quick and simple tensammetric method of estimation of non-ionic surfactants (NS) in aqueous solutions is proposed. The method makes use of the variation in the differential capacity of double layer in relation to the time of accumulation (C(d)-t(acc)) of non-ionic surfactants at the hanging mercury drop electrode, generated by a single, very quick opening of the valve. Under such conditions, the capacity current measured at the potential of maximum adsorption diminishes with accumulation time of non-ionic surfactants. The proposed method, which was verified for model surfactant (Triton X-100), may also be applied in the determination of other NS. Modifications in construction of the CGME electrode and its improved metrological parameters played an important role in the presented procedure. In addition, other measurements were performed using standard electrochemical techniques, whereby current-time and differential capacity-potential curves were recorded. Satisfactory results were obtained in the determination of Triton X-100 in the range from 0.05 to 20 mg L(-1) (R.S.D.=6%, recovery=94-103%, r=0.999, DL=0.15 mg L(-1)). Applicability of the method was presented using the water samples from Bia?ka and Dunajec rivers, from which NS were removed by addition of fumed silica.     

Studies on the electrocapillary curves of anionic surfactants in presence of non-ionic surfactants

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 > Aerosol IB while the shift in maxima is in the order Aerosol IB ~ Manaxol OT > SLS which confirms association of cationic characteristics with the micelles of these non-ionic surfactants. The magnitude of the shift in electrocapillary maxima is Nonex 501 > Nonidet P40 > Tween 20 > Tween 40 which may be the order of magnitude of the positive charge carried by these non-ionic surfactants.     

Surfactant-sensitized post-column reaction with xylenol orange for the determination of lanthanides by ion chromatography

The presence of the cationic surfactants cetylpyridinium chloride and hexadecyltrimethylammonium bromide in an alkaline 40% methanol medium was found to enhance sensitivity when xylenol orange is employed as the post-column reaction reagent for the determination of lanthanides by dynamic ion chromatography. Detection of individual lanthanides was carried out at 618 nm after separation by cation-exchange chromatography with gradient elution on a C₁₈ column. The eluent was -hydroxyisobutyric acid-sodium octanesulfonate, pH 3.8. Sensitivity enhancements by factors of three to six, compared with xylenol orange alone, were achieved at a cationic surfactant concentration of 2.4 mM. The calibration response was linear in the 0.05 to 5 μg ml⁻¹ analyte concentration range. Limits of detection below 3 ng were obtained for all the natural lanthanides and lanthanum. No sensitivity enhancement effects were observed with anionic (sodium dodecyl sulfate) and non-ionic (Triton X-100) surfactants under the conditions tested.     

Electrochemical masking of large amounts of copper in dpasv and the determination of thallium in the presence of a large excess of copper

The influence of the following surfactants on the peak of copper in 0.2M EDTA at pH 4.5 was investigated: polyoxyethylated alkylphenols having an average of 3 and 9.5 ethylene oxide units; polyoxyethylene alcohols having 4 and 7 ethylene oxide units; poly(ethylene glycols) having M.W. 4000, 9000 and 20000; hexadecyltributylphosphonium bromide (HDTBPB), tetraphenylphosphonium bromide (TPPB),N,N,N,N,N',N',N-examethylhexamethylenediammonium bromide (HMB), benzyl(di-isobutylphenoxyethoxy) dimethylammonium chloride (Hyamine 1622), hexadecyltrimethylammonium bromide (HDTMAB), hexadecyldimethylbenzylammonium chloride (HDDMBAC) and tetrabutylammonium chloride (TBAC). HDDMBAC, as well as all the substances examined which contained an ethylene oxide chain, completely suppressed the copper peak. HDTBPB and TPPB partially suppressed the peak, whereas HDTMAB, HMB and Hyamine 1622 enhanced it. TBAC was without effect. In 0.2M EDTA at pH 4.5 containing TBAC at 0.01M concentration and 10 ppm of Rokafenol N-3, Cu(II), Pb(II) and Bi(III) can be tolerated at concentrations of up to 0.05M, the height of the thallium peak being unaffected. The precision of the determination (3–10%) and the recovery are satisfactory. A 10³-fold ratio of Fe(III) to Tl(I) does not interfere with the determination.     

Spectrophotometric and Thermodynamic Studies of Micellar Interaction of Surfactants with p-Nitrophenol

Interaction of p-nitrophenol (NPH) with various surfactants, viz., cetylpyridinium chloride (cationic), sodium dodecylsulphate (anionic) and Triton X-100 (nonionic) are studied spectrophotometrically, in aqueous-micellar medium. The interactions are of electrostatic as well as hydrophobic nature. The strength of interaction is represented in terms of the equilibrium constants and other thermodynamic quantities of formation of the p-nitrophenol-micelle donor-acceptor complexes in addition to a shift in the acid-base equilibrium of NPH. The interaction between NPH and CPC is much stronger that with Triton X-100 whereas the interaction with SDS is very weak. Formation of 1:1 charge transfer (or electron donor-acceptor) complex is evidenced from the results. The interaction of NPH is enthalpy driven with CPC and entropy driven with Triton X-100.     

Micellar extraction preconcentration of barium with phases of nonionic surfactants at the cloud point

The micellar extraction of barium with phases of nonionic surfactant Triton X-100 was studied in the presence of aliphatic monocarboxylic acids, crown ethers, and Carboxyarsenazo and its mixtures with cetylpyridinium chloride and octylamine. It was shown that the complete extraction of barium into the micellar phase was attained using Carboxyarsenazo and cationic surfactants in the presence of octylamine through the formation of a ternary hydrophobic complex. The conditions for the determination of the atomic absorption of barium in water with preconcentration into the nonionic surfactant phase at the cloud point temperature were developed.     

In situ synthesis and preconcentration of cetylpyridinium complexed hexaiodo platinum nanoparticles from spent automobile catalytic converter leachate using cloud point extraction

In the present study, a green chemistry based cloud point extraction (CPE) method has been developed for the in situ synthesis and preconcentration of cetylpyridinium complexed hexaiodo platinum nanoparticles (Pt-I NP) from the leachate of spent automobile catalytic converter using potassium iodide (KI) and assisted by a combination of cationic and non-ionic surfactants; cetylpyridinium bromide (CPB) and Triton X-114, respectively. The process parameters such as concentrations of hydrochloric acid, platinum, KI, sodium chloride, CPB, Triton X-114; incubation temperature and complexation time on CPE were optimized. The synthesized nanoparticles were characterized by UV–visible spectroscopy (UV–vis), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and zeta potential techniques. The formation of Pt-I NP was followed with UV–vis. The XRD pattern established the tetragonal crystal structure of the produced nanoparticles. The nanoparticles were spherical in shape and the particle size obtained with TEM was about 5.6 nm. Further, the preconcentrated nanoparticles were quantified by continuum source electro-thermal atomic absorption spectrometry (ET-AAS) and a preconcentration factor of 25 was obtained for a reaction volume of 25 mL. The accuracy of the developed method was confirmed by analyzing the certified reference materials such as CCRMP PTM-1a (copper-nickel sulphide matte) and CCRMP PTC-1a (copper-nickel sulphide concentrate). The current CPE protocol demonstrates advantages such as simultaneous synthesis and preconcentration; synthesis at micromolar concentration from metal scrap, higher nanoparticle recovery; biodegradability and biocompatibility of the employed surfactants and dual solubility of the synthesized Pt-I NP. Thus, the developed method can be applied for the separation, large scale synthesis and preconcentration of Pt-I NP from various environmental and industrial wastes, in a single pot.     

Mixed Adsorption Layers of Nonionic and Cationic Surfactants on Quartz

Surfactant adsorption on quartz and wetting of glass by aqueous solutions of tetradecyltrimethylammonium bromide, Triton X-100, and their mixtures are studied. It is shown that synergistic adsorption of surfactants from mixed solutions occurs in the region of low concentrations. In the region of high concentrations, mixed molecular aggregates of the cationic and nonionic surfactants are formed on the surface. The structure of the mixed adsorption layers is discussed.     

Correlation between surface free energy of quartz and its wettability by aqueous solutions of nonionic, anionic and cationic surfactants

The measurements of the advancing contact angle for water, glycerol, diiodomethane and aqueous solutions of Triton X-100 (TX-100), Triton X-165 (TX-165), sodium dodecyl sulfate (SDDS), sodium hexadecyl sulfonate (SHDS), cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPyB) on quartz surface were carried out. On the basis of the contact angles values obtained for water, glycerol and diiodomethane the values of the Lifshitz–van der Waals component and electron-acceptor and electron-donor parameters of the acid–base component of the surface free energy of quartz were determined. The determined components and parameters of the quartz surface free energy were used for interpretation of the influence of nonionic, anionic and cationic surfactants on the wettability of the quartz. From obtained results it was appeared that the wettability of quartz by nonionic and anionic surfactants practically does not depend on the surfactants concentration in the range corresponding to their unsaturated monolayer at water–air interface and that there is linear dependence between adhesional and surface tension of aqueous solution of these surfactants. This dependence for TX-100, TX-165, SDDS and SHDS can be expressed by lines which slopes are positive. This slope and components of quartz surface free energy indicate that the interaction between the water molecules and quartz surface might be stronger than those between the quartz and surfactants molecules. So, the surface excess of surfactants concentration at the quartz–water interface is probably negative, and the possibility of surfactants to adsorb at the quartz/water film–water interface is higher than at the quartz–water interface. This conclusion is confirmed by the values of the adhesion work of “pure” surfactants, aqueous solutions of surfactants and water to quartz surface. In the case of the cationic surfactants the relationship between adhesional and surface tension is more complicated than that for nonionic and anionic surfactants and indicates that the relationship between the adsorption of the cationic surfactant at water–air and quartz–water interface depends on the concentration of the surfactants in the bulk phase.     

Dynamic Interfacial Tension of Surfactant Mixtures at Liquid-Liquid Interfaces

Dynamic interfacial tensions for surfactant mixtures at liquid-liquid interfaces were obtained with a drop volume tensiometer. The surfactants tested were Triton X-100, palmitic acid, and Span 80 at both the water-hexadecane and water-mineral oil interfaces. Two-surfactant mixtures were examined with the surfactants initially dissolved in different phases to minimize bulk-phase interactions. For concentrations below the CMC, it was found that the adsorption kinetics of palmitic acid and Triton X-100 mixtures were dominated by the latter surfactant. Apparent diffusion coefficients were obtained for Triton X-100 both in the absence and in the presence of palmitic acid. These values were largely insensitive to the presence of palmitic acid. For mixtures of Span 80 and Triton X-100, the adsorption kinetics were found to be influenced significantly by both surfactants. In this case, relative changes in surfactant concentrations affected the dynamic interfacial tension of the mixed system. A previously proposed multicomponent adsorption model described the dynamic interfacial tension adequately at low concentrations of Triton X-100, when desorption could be neglected. At higher concentrations, modifications were needed to account for solubilization into the oil phase. These corrections allowed the model to describe the long time adsorption quite well. However, predicted values of short time interfacial tensions were overestimated, likely due to a synergistic interaction of the two surfactants. Copyright 1999 Academic Press.     

Flotation and adsorption investigations of the systemn-dodecanoic acid/mercury at different pH values

The systemn-dodecanoic acid/mercury in 0,1 N KCl solutions has been investigated within pH range 4,0–10,5 in order to characterize the adsorption of surfactant and to determine its influence on the flotation of mercury. Flotation tests have been carried out in a model mercury flotation apparatus developed by Pomianowski and Para. Some characteristic parameters of adsorption (attraction constant of Frumkin isotherm, adsorption coefficient at maximum adsorption potential, free standard adsorption enthalpy and area per molecule) have been determined by a. c. polarographic capacity-potential and capacity-time curves. Flotation recovery as well as attraction constant, adsorption coefficient and surface excess reach maximum at pH5,1. It is explained by the assumption of an ion-molecule associate formation.Publ.-No. 810 from Research Institute of Mineral Processing, Academy of Sciences of the German Democratic Republic, Freiberg     

Phase Separation Phenomenon in Non-ionic Surfactant TX-114 Micellar Solutions: Effect of Added Surfactants and Polymers

Clouding (or phase separation) in non-ionic surfactants is a well-known phenomenon. Clouding is to be avoided in some applications whereas in others it is preferred. Herein the results of CP (cloud point—the temperature at which solution separates into two phases) measurements of the non-ionic surfactant Triton X-114 (TX-114) in the presence of surfactants and polymers are presented. Cationic and nonionic surfactants, in the absence and presence of the quaternary salt tetrabutylammonium bromide (TBAB), increase the CP of TX-114. Anionic surfactants, in the absence of TBAB, increase the CP; in the presence of TBAB, these surfactants decrease the CP. Polymers of PEG and PVP series have been found to decrease the CP. The results are discussed by taking into consideration the nature of the added surfactants and polymers.     

Adsorption of cationic and nonionic surfactants on a SiO<Subscript>2</Subscript> surface from aqueous solutions: 1. Adsorption of dodecylpyridinium bromide and Triton X-100 from individual solutions

Adsorption of cationic surfactant dodecylpyridinium bromide and nonionic surfactant Triton X-100 from aqueous solutions on the surface of SiO₂ particles is studied at various pH values (3.6, 6.5, and 10). The data on the adsorption are compared with the data on the wetting of quartz plates by solutions of these surfactants. Adsorption of both studied surfactants on the SiO₂ surface is greatly dependent on solution pH. The mechanism of adsorption of the cationic surfactant is shown to be changed when passing to the alkaline pH region. Triton X-100 does not demonstrate a substantial change in the adsorption mechanism in the pH range from 3.6 to 10.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 274–280.Original Russian Text Copyright © 2005 by Kharitonova, Ivanova, Summ.     

Surface enhanced Raman scattering of surfactants adsorbed on silver mirror surfaces

The surface enhanced Raman scattering (SERS) spectra of two surfactants: Triton X-100 and n-hexadecylpyridinium bromide adsorbed on the interfaces between chemically reduced silver mirrors and water are obtained. By comparing and analyzing their bulk and SERS spectra, we have studied the adsorption configurations of the two surfactants on the silver/water interfaces.     

Surfactant effects on the spectrophotometry of the gadolinium—chrome azurols complex

Increased molar absorptivities and red-shifted absorbance maxima were noted only upon the addition of cetylpyridinium chloride (CPC), a cationic surfactant. A 1:2:4 gadolinium/chrome azurol S/CPC complex was forned but dissociated at [CPC]/ [Gd³⁺] > 4 apparently because gadolinim(III) was displaced from this complex by additional surfactant monomers. Ternary complexes having different stoichiometries formed in the presence of excess dye. Sodium dodecyl sulfate (SDS), an anionic suffactant, induced dissociation of the binary complex at micellar concentrations, suggesting that dissociation resulted from adsorption of Gd³⁺ cations on the negatively charged micellar surface. Addition of Triton X-100, a nonionic surfactant, had little effect at either micellar or submicellar concentrations. These results confirm that complex stability is an important factor in the use of surfactants as sensitizers in quantitative spectrophotometry.     

Adsorption Kinetics of Some Polyethylene Glycol Octylphenyl Ethers Studied by the Fast Formed Drop Technique

The adsorption kinetics of Triton X-100 and Triton X-405 at solution/air and solution/hexane interfaces is studied by the recently developed fast formed drop technique. The dynamic interfacial tension of Triton X-100 and Triton X-405 solutions against hexane has been measured without preequilibration of the water and oil phases. It is found that the dynamic interfacial tension of Triton X-100 solutions passes through a minimum. This strange behavior is attributed to partial solubility of the surfactant in hexane. Such minima of the dynamic interfacial tension of Triton X-405 solutions have not been observed, which correlates well with the solubilities of both surfactants in hexane reported in the literature. The dynamic surface tension of solutions of both surfactants and the dynamic interfacial tension of Triton X-405 solutions are interpreted by the Ward and Tordai model for diffusion controlled adsorption. It is shown that proper interpretation of the experimental data depends on the type of isotherm used. More consistent results are obtained when the Temkin isotherm is used instead of the Langmuir isotherm. The results obtained with Triton X-100 at the solution/air interface confirm that the adsorption of this surfactant occurs under diffusion control. The adsorption of Triton X-405 at solution/air and at solution/hexane interfaces seems to occur under diffusion control at short periods of time, but under mixed (diffusion-kinetic) control at long periods of time. A hypothesis is drawn to explain this phenomenon by changes in the shape of the large hydrophilic heads of Triton X-405 molecules. Copyright 2000 Academic Press.     

Synergistic adsorption of Triton X-100 and CTAB surfactants at the toluene + water interface

Equilibrium interfacial tension measurements at 25.0 °C of the toluene + water system with two widely used surfactants, octylphenol decaethylene glycol ether (Triton X-100) and cetyl trimethyl ammonium bromide (CTAB) having concentrations much lower than their CMC were performed. According to the obtained parameters from the Szyszkowski equation, Triton has higher adsorption tendency than of CTAB. The results obtained for surfactants mixtures are analyzed by the theory of non-ideal interactions in binary mixtures (NIBMs) and the interfacial composition and the interaction parameter in the mixed adsorbed monolayer are determined. The attractive interaction shows a maximum value at nearly equal surfactants bulk mole fraction. The synergism is achieved for Triton bulk mole fractions of 0.30 and higher, and the highest degree of synergism (40.6%) is found for the bulk mole fraction of 0.52 with the lowest investigated constant interfacial tension of 28.0 mN m⁻¹. A correlation was developed for variation of the interaction parameter with bulk mole fraction.     

Comparison of the utility of several tensammetric techniques for the determination of traces of surfactants after preconcentration at the hanging mercury drop electrode

After preconcentration of surfactants at the HMDE, four tensammetric signals were examined to establish the optimum conditions for the determination of ultratraces of surfactants in alkaline, neutral and acidic media. The signals studied were: (1) the depth of the depression occuring on the curves obtained in a.c. fundamental tensammetry; and (2–4) the height of the peaks on the curves obtained in a.c. fundamental tensammetry, a.c. second-harmonic tensammetry and differential pulse tensammetry, respectively. The lowest detection limits found for Triton X-100 and a polyethylene glycol (PEG-4000) were 10 and 2 μg dm^-3, respectively. Traces of surfactants found in supporting electrolytes (ca. 25 μg dm^-3) gave desorption peaks at potentials around ?1 V. These contaminants had no significant effect on the peaks on Triton X-100 and PEG-4000 and they affected the SDS peak markedly. The reproducibility of the results obtained for SDS was poorer than for Triton or PEG.     

Cationic Surfactants as Regulators in Paper Separation of 2‐Nitrophenol and 2,4,6‐Trinitrophenol in Water

The chemical pollutants 2‐nitrophenol (2‐NP) and 2,4,6‐trinitrophenol (2,4,6‐TNP) were studied for their separation from water by the paper capillary permeation adsorption technique by the use of the four cationic surfactants dodecyltrimethylammonium chloride (DTAC), tetradecyltrimethylammonium bromide (TTAB), cetyltrimethylammonium bromide (CTAB), cetylpyridinium chloride (CPC) as regulators. The effect of pH and the concentration of surfactant on the separatability have been investigated. A nearly 100% separatability was obtained for each pollutant at its optimum pH and surfactant concentration. It was shown that the separation was accomplished via surface adsorption onto the fibers of paper. The change in separatability at basic pH 11 with surfactant variety was analyzed. The result shows that the surfactant with a longer chain alkyl group is more effective for the separation of 2‐NP and the surfactants with 16 carbons in the long chain alkyl group are most effective. The surfactants with 12 carbons or more in the long alkyl group but containing no aromatic group such as pyridyl group are equally effective for accomplishing an efficient separation of 2,4,6‐TNP. Selective separation of 2‐NP from an admixture of 2‐NP plus 2,4,6‐TNP was attempted. The optimum surfactant for each pollutant was tested with seawater for removing the pollutant. The goal of this study is to search for an optimum cationic surfactant and optimum separation conditions for nitrophenols.