Enhancement of the fluorescence of the zinc-morin complex by a non-ionic surfactant

A method is described for the fluorimetric determination of zinc, based on formation of a zinc-morin complex in the presence of a non-ionic surfactant. The complex has practically no fluorescence in the absence of surfactant, but the addition of Genapol PF-20 (non-ionic surfactant, ethylene oxide-propylene oxide condensate) makes possible the fluorimetric determination of low concentrations of zinc as it enhances the fluorescence of the complex about 75-fold. Maximum fluorescence is produced at pH 4.7 +/- 0.2 (acetic acid-acetate buffer), with 1.5% surfactant and 0.009% morin. The fluorescence is excited at 433 nm and measured at 503 nm. The calibration graph is linear up to 150 ng/ml zinc concentration and the detection limit is 3 ng/ml. The relative standard deviation (11 replicates) is 2.4% for zinc at 20 ng/ml concentration and 1.7% for 100 ng/ml. Of 29 ions studied, Al(3+), Be(2+), Zr(4+) and Cd(2+) strongly increase the fluorescence of the system, and Fe(3+), Ni(2+), Cu(2+), Ti(IV) and Co(2+) decrease the fluorescence signal.     

Electrostatic effects in films stabilised by non-ionic surfactants

The disjoining pressure Pi of films of aqueous octyl-beta-glucoside (beta-C(8)G(1)) solutions with and without salt was measured as a function of the film thickness by means of a thin film pressure balance. The analysis of the experiments confirms the presence of an electrostatic double layer which dominates the long-range interactions as found in previous experiments with other non-ionic surfactants in the presence of added salt. In the absence of salt, we find a local ion concentration much higher than that of the residual ionic impurities present in the bulk solution.     

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.     

Determination of critical micelle concentration of non-ionic surfactants by electrocapillary curves

A method is described for the determination of the critical micelle concentration of non-ionic surfactants by measurement of their effect on the electrocapillary curves for a dropping mercury electrode. The method was compared with the iodine-solubilization, surface tension, and polarographic maximum suppression methods.     

Determination of poly(oxyethylene) non-ionic surfactants by two-phase titration

The solvent extraction of non-ionic surfactants with sodium hydroxide and tetraphenylborate has been studied, and a method developed for the determination of non-ionic surfactants by two-phase titration. A hydrophobic indicator system was used. The method is valid only when the concentration of anionic surfactant in the sample solution is lower than 1 x 10(-4)M.     

A radiometric method for the determination of non-ionic surfactants

A radiometric method for the determination of non-ionic surfactants of ethylene oxide type has been elaborated. The principle of the method is the formation of an associate¹³³Ba-non-ionic surfactant — dicarbolide and its extraction into a mixture nitrobenzene-chloroform /41/. The extracted activity of¹³³Ba is proportional to the non-ionic surfactant concentration in the sample. The factors influencing the determination of non-ionic surfactants in the real waste solution after washing have been studied. The possibility of the determination of non-ionic surfactants by the calibration graph method and by the method of standard addition was verified.     

Extractive spectrophotometric determination of non-ionic surfactants in water

The solvent extraction of non-ionic surfactants with potassium chloride and tetrabromophenolphthalein ethyl ester potassium salt has been studied, and a method developed for determining trace amounts of non-ionic surfactants in water spectrophotometrically. Various non-ionic surfactants of general type RO(CH(2)CH(2)O)(n)H (where R is an alkyl or alkylphenyl group and n is the number-average degree of polymerization) are extracted quantitatively into o-dichlorobenzene from the water sample, and reacted in the organic phase with tetrabromophenolphthalein ethyl ester potassium salt to give a coloured product, the absorbance of which is measured at 620 nm.     

Investigation of colloidal properties of modified silicone polymers emulsified by non-ionic surfactants

An orchid-like polyaniline (PANI) structures was synthesized by initialing the polymerization at 80 °C and growing at 25 °C using ethanol and water as co-solvent in the presence of toluene-p-sulfonic acid (p-TSA) as the dopant. The "flowers" are consisted of 8-14 pieces of "petals" with 5-8 μm in length. By adjusting the molar ratio of p-TSA/aniline, the cooling rate and the component of the solvent, flake-like and peony-like morphology can also be obtained. The formation mechanism of the orchid-like structure is proposed.     

Determination of alkylphenol- and alkylalcohol-based non-ionic surfactants by a derivative chronopotentiometric method

The adsorption of surfactants at a dropping mercury electrode and at a hanging mercury drop electrode has been studied. The DME is more suitable for analytical purposes. For quantitative work the size of the indentation in the dE/dt-curve at the potential of desorption is used. A crude classification of surfactants is possible on the basis of the form of the dE/dt-curve.     

Modification of reversed-phase separations of small molecules using non-ionic surfactants and mixed ionic-non-ionic surfactants

The effects of non-ionic surfactants, Tween 20 and Tween 60, on reversed-phase separations of small molecules have been examined. Tween compounds were found to partition irreversibly into the ODS material used, markedly decreasing capacity factors for the compounds tested. Compounds which could hydrogen bond were less affected. Ion pairing using either anionic or cationic surfactants was possible in the presence of the non-ionic surfactants. While reversed-phase effects predominate under these conditions, secondary effects on retention order were observed and attributed to hydrogen bonding. Primary amines were retained longer than the corresponding secondary amine while catechols were retained longer than the corresponding methoxyphenols.     

Adsorption of surfactants on low-charged layer silicates Part II: Adsorption of non-ionic surfactants

Nonionic surfactants were adsorbed on low-charged layer silicates in the interlayers. After drying, the surfactants were arranged in densely packed double layers. However, in suspension considerably higher basal spacings are measured by x-ray diffraction which indicate that large quantities of non-ionic surfactants are adsorbed. With the aid of calorimetry, enthalpies of displacement were recorded which suggest strong interactions of the non-ionic surfactants with smectites. In analogy to tests on hydrophilic SiO₂, the adsorption of smectites is found to depend on the degree of ethoxylation of the non-ionic surfactant. The adsorption declines with increasing EO content.List of symbols n ^s adsorbed amount of surfactants (mmol/g) - n _max ^s maximal adsorbed amount of surfactants - d _L basal spacing (nm) - d _L interlayer separation because of adsorption - V _M molar volume of surfactant - V _max ^s volume of adsorbed surfactants (cm³/g) - V _int volume between the silicate layers (interlayer volume) (cm³/g) - H enthalpy of displacement (J/g) - h _max max. molar enthalpy of displacement (kJ/mol) Part I: Prog. Colloid Polymer Sci. 84, 206This paper is part of W. Röhl's doctorial dissertation at the Heinrich-Heine University, Düsseldorf     

Separation and determination of non-ionic surfactants of the nonylphenol polyglycol ether type by liquid chromatography

A normal-phase method for the separation and determination of non-ionic surfactants of the 4-nonylphenol polyglycol ether (NPEO) type by liquid chromatography is described, based on a LiChrosorb-Diol column and nonpolar linear gradient elution, with spectrophotometric detection at 275 nm. The method was applied to the determination of NPEO oligomers in the technical surfactants Arkopal N-20, N-40, N-60 and N-100 and in aqueous solutions from flotation processes. The relative standard deviations were 2.47–5.62%. The detection limits for nonylphenol polyglycol ether with 2, 4, 6, 8, 10, 13 and 15 ethoxy units were 51, 57, 64, 74, 85, 118 and 132 ng, respectively. The method can also be used for the determination of other alkylphenol polyglycol ethers. Reversed-phase LC with an octadecylsilica column was investigated and can be applied to the identification of the alkyl group present.     

An extraction—spectrophotometmc method for the determination of non-ionic surfactants

The surfactant is extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozincate(II), and zinc(II) in the extract is determined spectrophotometrically after addition of l-(2-pyridylazo)-2-naphthol and triethanolamine. With a 150-ml water sample, the limit of detection is 15 μg l^-1 (as Triton X-100). The method requires only one extraction and is applicable, without modification, to fresh, estuarine and sea-water samples.     

An atomic absorption spectrometric method for the determination of non-ionic surfactants

A method is described for the determination of non-ionic surfactants in the concentration range 0.05–2 mg l^-1.Surfactant molecules are extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozincate(II) and the determination is completed by atomic absorption spectrometry. With a 150-ml water sample, the limit of detection is 0.03 mg l^-1(as Triton X-100).The method requires a single phase separation step, is applicable, without modification, to fresh, estuarine and sea-water samples and is relatively free from interference by anionic surfactants; the presence of up to 5 mg l^-1 of anionic surfactant (as LAS) introduces an error of no more than 0.07 mg l^-1 (as Triton X-100) in the apparent non-ionic surfactant concentration.     

The partition of ethoxylated non-ionic surfactants between two non-miscible phases

The partition of a polydispersed ethoxylated non-ionic surfactant in equilibrated oil–water systems has been studied at 25 °C. The model surfactant used was a commercial sample of nonylphenol ethoxylated with 10 moles of ethylene oxide (NPEO₁₀). The partition isotherms over the range of surfactant concentration including the critical micelle concentration (CMC) were made with n-hexane, i-octane and n-decane as oil phases. Each partition isotherm exhibits a change of slope that matched the CMC value of surfactant determined by surface tension measurements on aqueous solutions. During the partition of NPEO₁₀ in the oil–water systems, the oligomer distribution in the oil and water phases changed because of fractionation. Below CMC, the mean ethoxylation degree in the oil phase was smaller, whereas in water it was higher than the mean initial value of the surfactant. Moreover, the mean ethoxylation degree in both oil and water phase was practically independent of surfactant concentration. Above CMC, the mean distribution of ethoxymers decreased in both phases. This was ascribed to the competition between micelles from water and the oil phase for the more hydrophobic species of the surfactant. The mean distribution of ethoxymers in the aqueous phase asymptoted to a value that was the mean of the surfactant itself, whereas it steeply decreased in the organic phase.     

Sources of error in the determination of non-ionic surfactants in environmental samples

The analytical procedures for the determination of non-ionic surfactants (NS) consist of sampling, multistage separation and final determination. Each of these stages is a potential source of error. 33% of an initial amount of 100 g NS may be lost due to adsorption on the walls of glass vessels during storage or 55% in the case of polyethylene vessels. Ineffective preservation of samples leads to very quick biodegradation of NS and incorrect results. Chloroform, frequently used for this purpose, is ineffective, whereas formaldehyde gives satisfactory results. Also during the separation procedure substantial fractions of NS are lost. The currently used methods enable the determination of NS having 5–30 oxyethylene subunits only. In the extraction with ethyl acetate NS having long oxyethylene chain remain in the water phase or are caught at the interface. If looked at carefully these analytical procedures show serious drawbacks. The washing of the precipitate in the BiAS procedure causes a dramatic loss of precipitate. The recommended use of G4 glass filters also leads to loss of precipitate. Instead, the use of G5 gives satisfactory results. The choice of one surfactant as the standard, necessary for the determination of the total concentration of a mixture of unknown composition, possibly consisting of several hundred of individual compounds, can be also a serious source of error. The higher is the difference between the slopes of the calibration curves of the mixture components, the higher is the error. Two newly developed techniques, namely the indirect tensammetric method (ITM) and the BiAS procedures combined with the ITM give better results than the procedures currently recommended.