催化动力学光度法测定阴离子表面活性剂

基于在H2SO4介质中,阴离子表面活性剂对高碘酸钠氧化罗丹明B褪色的反应具有较强的催化作用,建立了测定阴离子表面活性剂的催化动力学光度法.本文以十二烷基硫酸钠为标准品进行实验,线性范围为0.08～0.20 mg/L,检出限为0.0193 mg/L.用于水样中阴离子表面活性剂总量的测定,测定结果的相对标准偏差为1.3%～1.4%,回收率为104%～106%.     

Methods for the determination of anionic surfactants

Methods for the determination of synthetic anionic surfactants published in the past two decades are considered, and their advantages and disadvantages are demonstrated. Spectrophotometric and potentiometric (with the use of ion-selective electrodes) techniques, including flow injection analysis versions, are used for the determination of anionic surfactants. Chromatographic techniques (primarily, high-performance liquid chromatography) are most frequently used for the separation, preconcentration, and determination of anionic surfactants in complex mixtures. Spectrofluorimetry, voltammetry, and immunoassay did not find wide application.     

Solid-contact potentiometric sensors based on ion pairs of cetylpyridinium with dodecylsulfate and tetraphenylboratc for various surfactants

Compositions of active membrane components for solid-contact potentiometric sensors selective to various surfactants were proposed. The stoichiometric ratios of components and the solubility and thermal stability of organic ion-exchangers were estimated. The main electroanalytical parameters of sensors were determined. Procedures for the potentiometric determination of nonionic surfactants in wastewater, cationic surfactants in hair rinses, and separate determination of nonionic and anionic surfactants in shampoos and synthetic detergents were developed. Presented at the V All-Russian Conference with the Participation of CIS Countries on Electrochemical Methods of Analysis (EMA-99), Moscow, December 6–8, 1999.     

Detection of bioactive surfactants in aqueous solutions on the basis of H2O2-voltammetry

The voltammetric determination of surfactants at the hanging mercury drop electrode in aqueous solutions is described, based on the shift of the peak potential deltaEp or the increase of the peak height deltaip of the electroreduction of hydrogen peroxide or of the second oxygen reduction step, with increasing concentration of surfactants. Although the selectivity of this method is rather limited, it could be utilized, e.g., for monitoring the absence (or presence) or for the determination of the contents of specified surfactants by comparing the obtained deltaip (deltaEp) signal with the reference state of the system or with that of a selected reference surface active substance. As model surfactants n-octanol, tetrabutylammonium chloride and sodium dodecylbenzenesulfonate were used, the regular adsorption behavior of which is well known. The method was successfully applied to control the presence of a commercial detergent in water for rinsing bottles for infusion solutions.     

Determination of the Critical Micelle Concentration of Cationic Surfactants by Capillary Electrophoresis

The determination of the critical micelle concentration (CMC) of cationic surfactants by capillary electrophoresis was demonstrated. In this study, tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DoTAB) were selected as cationic surfactants and propazine was chosen as test solute. In the evolution of the effective electrophoretic mobility of propazine as a function of surfactant concentration, a dramatic change in slope at a particular concentration is a good indication of the CMC of this surfactant. The CMC values determined experimentally were further confirmed by a curve-fitting approach. Simulation of the electrophoretic mobility curves as a function of surfactant concentration in both micellar electrokinetic chromatography and capillary zone electrophoresis using cationic surfactants as an electrolyte modifier was performed for propazine, and the intersection of these two mobility curves allowed us to precisely predict the CMC of the surfactant. The CMC values determined for TTAB and DoTAB are 1.6 ± 0.1 and 11.0 ± 0.1 mM, respectively, in the case of an electrolytic solution consisting of 70 mM phosphate buffer at pH 6.0. Moreover, the applicability of the electroosmotic mobility as a parameter for the determination of the CMC was examined.     

TiC Working Electrode. Voltammetric Characteristics and Application for Determination of Lead Traces by Stripping Voltammetry

The TiC working electrode was tested as a novel, potential electrode for anodic stripping voltammetric determination of lead(II) ions traces. To demonstrate the practical applicability of the TiC electrode, an underpotential deposition/dissolution (UPD) phenomena system in electrolyte without removal of oxygen was tested. The electrode was constructed be means of mounting a TiC disk (Ø=3.5 mm) in a resin body. Three compositions of TiC were tested differing in stoichiometry, namely TiC_0.6, TiC_0.8, and TiC_1.0. The key problem is the method of electrochemical activation of the TiC electrode. No or improperly activated electrode is not polarized and is unsuitable as a voltammetric sensor. The TiC electrode was used for the determination of Pb²⁺ in concentrations ranging from 1 to 100 nM. The instrumental parameters, composition of supporting electrolyte and procedures of the electrode activation were optimized. The repeatability of DP ASV runs in synthetic solutions covering the entire concentration range is better than 3%. The calibration curve is characterized by a correlation coefficient of at least 0.999. The detection limit was 2 nM for an electrodeposition time of 30 s. The method enables determination of Pb²⁺ in the presence of, among the others, high excesses of Cd, Cu, In, Sb, Se, and Tl ions as well as surfactants, Triton X‐100 and humic acids. The analysis of Pb²⁺ in synthetic solutions with and without surfactants, certified reference material and natural water samples have been performed. The voltammetric data were associated with the structural characterization of the electrode surface using scanning electron microscopy (SEM) and X‐ray fluorescence spectroscopy (XRF).     

Ion-association compounds of anionic surfactants with iron(II)chelates: Part II. Selective determination of surfactants

Homologous anionic surfactants may be separated from each other by solvent extraction of their ion-association compounds with iron(II) chelates. Separations of components from a number of surfactant mixtures were investigated, and the effect of solution variables on extraction and separation was studied. A method is proposed for the determination of surfactants of various chain lengths. Applications of this method to synthetic mixtures and to biodegradation experiments are described.     

Sensitive measurement of methylene blue active substances by attenuated total reflection spectrometry with a trimethylsilane-modified glass slab optical waveguide

Attenuated total reflection spectrometry with a slab optical waveguide (SOWG) was explored for the simple, rapid and sensitive measurement of total anionic surfactants by the methylene blue active substance (MBAS) method. A fused-silica sheet used as a guiding layer was modified with trimethylsilane (TMS) to extract and concentrate the MBASs on the SOWG surface. Based on preliminary studies of the adsorption behavior and visible ATR spectrum of MB on the modified silica surface, a detection wavelength of 600 nm was chosen for the sensitive measurement of anionic surfactants. When the concentration of MB was set at 10 microM in the final measurement solution, the calibration curve for a typical anionic surfactant (sodium dodecylbenzenesulfonate) was linear up to 0.6 microM and the detection limit was 0.07 microM. The proposed method was applied to the determination of total anionic surfactants in river water.     

Detection of bioactive surfactants in aqueous solutions on the basis of H2O2-voltammetry

The voltammetric determination of surfactants at the hanging mercury drop electrode in aqueous solutions is described, based on the shift of the peak potential ΔE_P or the increase of the peak height Δi_P of the electroreduction of hydrogen peroxide or of the second oxygen reduction step, with increasing concentration of surfactants. Although the selectivity of this method is rather limited, it could be utilized, e.g., for monitoring the absence (or presence) or for the determination of the contents of specified surfactants by comparing the obtained Δi_P (ΔE_P) signal with the reference state of the system or with that of ¶a selected reference surface active substance. As model surfactants n-octanol, tetrabutylammonium chloride and sodium dodecylbenzenesulfonate were used, the regular adsorption behavior of which is well known. The method was successfully applied to control the presence of a commercial detergent in water for rinsing bottles for infusion solutions.     

Determination of homologues anion surfactants in technical preparations using a multisensor system and HPLC

New potentiometric solid-contact sensors with polyvinyl chloride membranes based on compounds of alkyl sulfates with cationic complexes copper(II)–organic reagent are proposed for the determination of synthetic anionic surfactants (ASs). Multisensor systems are developed for the quantitative determination of ASs in raw technical preparations (alkylbenzene sulfonates, alkyl sulfates, and sodium cocosulfate).     

Rapid Determination of Anionic Surfactants in Seawater under Shipboard Conditions

An installation for the rapid determination of surfactants in seawater using ion-selective electrodes was developed. The serviceability of the electrode was examined with reference solutions, and the electromotive force of the measuring circuit was found to be a linear function of surfactant concentration over the range 10^–6–10^–2M. The detection limit for anionic surfactants was 0.3 mg/L. The ranges of random errors in the determination of surfactants were calculated using a set of measurements within a series and between series of check samples to be about 0.7 and about 6 rel %, respectively. The installation was tested under on-site conditions on shipboard in the course of integrated marine studies of environmental conditions in the Baltic Sea. Maximum marine pollution levels were detected in the near-shore zone; this fact can be explained by waste discharge from sites where surfactants are in wide residential and industrial use.     

Separation of synthetic food colourants in the mixed micellar system. Application to pharmaceutical analysis

The paper presents a rapid method for the determination of commonly used synthetic food dyes by micellar electrokinetic capillary chromatography. Detection and separation conditions allowing complete resolution of 15 synthetic food colourants were investigated. The effect of different surfactants on the analytes mobility in relation to their structure was tested. After optimization procedure a dual micellar system was selected. All food dyes were separated in less then 20 min using a fused silica capillary in the borate/dodecylsulfate/deoxycholate buffer containing acetonitrile as organic modifier. The detection wavelength was set at 210nm. The method was successfully validated by determination of linearity ranges, detection limits, precision and repeatability for all colourants tested. In order to apply the method for pharmaceutical analysis a sample pretreatment procedures were found. Liquid pharmaceuticals were used as it or just after dilution with water. From tablets or capsules the colourants were isolated by adsorption on acidic aluminium oxide. The method was used for identification and if possible for quantification the synthetic food dyes in pharmaceuticals. The analytes are detectable at a concentration level 0.3-0.8 microg ml(-1).     

Determination of cinnamic acid by capillary zone electrophoresis using ion-pair reagents

The behavior of cinnamic acid in the presence of ion-pair reagents has been studied. Conditions have been chosen for the selective determination of cinnamic acid by capillary zone electrophoresis with normal and reversed polarity and spectrophotometric detection; the results have been applied for the analysis of drinks and milk hydrolysates. The influence of surfactants (sodium dodecyl sulfate, sodium octyl sulfonate) present in the buffer electrolyte on the efficiency of cinnamic acid determination is discussed.     

Liquid chromatography/electrospray ionisation mass spectrometric investigations of imidazoline corrosion inhibitors in crude oils

The so-called imidazolines (2-alkyl-1-[ethylalkylamide]-2-imidazolines and 2-alkyl-1-ethylamine-2-imidazolines) are a group of surface-active compounds, complex mixtures of which are used by various industries as surfactants and corrosion inhibitors. Although their industrial synthesis was reported over 100 years ago, few methods for the determination of individual imidazolines in mixtures, including industrial matrices such as crude oils, have been reported. Here we demonstrate that spiking of crude oils with synthetic imidazolines followed by solid-phase extraction and liquid chromatography/electrospray ionisation multistage mass spectrometry (LC/ESI - MS(n)) allows an estimation of low (<10) parts per million concentrations of individual imidazolines in crude oils. Whilst non-optimised at present, the method is a significant advance and may prove useful not only for improving an understanding of the mechanisms of industrial imidazoline synthesis and for monitoring downhole and topside oilfield operations, but also for the determination of the fate of imidazoline-based oilfield corrosion inhibitors and surfactants in the environment.     

Determination of Bismuth by Adsorptive Stripping Voltammetry Using Aluminum Oxide for Elimination of Environmental Sample Matrix Interferences

The aim of this work was to find a fast new and simple method for efficient elimination of negative influence of humic substances and synthetic surfactants in the voltammetric determination of bismuth. The negative influence of the organic matrix present in environmental water samples due to their adsorption on aluminum oxide was successfully evaluated. The organic compounds such as humic substances and surface active compounds were removed by adsorption on the surface of aluminum oxide from the water samples. The application of this method was the recovery of Bi(III) from spiked water samples.     

Determination of cationic surfactants in water samples by their enhanced resonance light scattering with azoviolet

A simple assay of cationic surfactants in water samples was developed based on the measurements of enhanced resonance light scattering (RLS). At pH 6.09 and ionic strength 0.03 M, the interactions of azoviolet (AV) with cationic surfactants, including zephiramine (Zeph) and cetyl trimethyl ammonium bromide (CTMAB), result in enhanced RLS signals characterized by the peaks of 470.0, 485.0 and 495.0 nm. The enhanced RLS intensity is proportional to the concentration of cationic surfactant of Zeph in the range of 0.2~6.0x10(-6) M, and to that of CTMAB in the range of 0.4~4.8x10(-6 )M. The limit of determination (3 sigma) is 2.1x10(-8) M and 3.8x10(-8) M for the two surfactants, respectively. Determinations of cationic surfactants in synthetic and tap water samples were successfully made with a recovery of 90.5~108.6%.     

稀土配合物的荧光衰减动力学特性和时间分辨光谱分析研究

研究了稀土配合物的荧光衰减动力学特性及其影响因素,拟定出长寿命组份存在下测定短寿命组份及短寿命组份存在下测定长寿命组份的2种时间分辨荧光光谱分析方法。用于纯稀土氧化物及合成水样中痕量铕和镝的测定,获得了满意的结果。     

Flow-Injection Differential Spectrophotometric pH Selectivity System for the Determination of Cyclamate Contaminants

A flow-injection system with differential spectrophotometric detection is proposed for the simultaneous determination of aniline and cyclohexylamine based on their reaction with 1,2-naphthoquinone-4-sulfonate (NQS). The pH is chosen to achieve selectivity since only aniline reacts at acidic pH whereas the two amines are derivatized in basic medium. The flow manifold comprises two reactors and two detection cells for developing and monitoring the reaction under selective and general (non-selective) conditions. A double beam spectrophotometer is used for differential detection, with two flow cells placed in the sample and reference holders. Figures of merit such as sensitivity, linear range, detection limit and precision are established. The evaluation of accuracy using a series of synthetic mixtures indicates overall prediction errors of 3% and 5% for aniline and cyclohexylamine, respectively. The method is applied to the determination of amine impurities in commercial sweeteners. Good concordance between the proposed and the standard chromatographic methods is found.     

Effect of Aqueous Phase pH on the Dynamic Interfacial Tension of Acidic Crude Oils and Myristic Acid in Dodecane

The time dependence of the interfacial tension between water–acidic crude oil and water–synthetic oil was investigated for aqueous phase pHs ranging from 2 to 9 using the du Noüy ring method at 20°C. Myristic acid in dodecane was selected as a model (synthetic oil) for acidic crude oil containing indigenous surfactants, and the similarities and differences between the dynamic interfacial tension behaviours of the natural and synthetic crude oil systems were compared. The initial interfacial tension and the relaxation of the interfacial tension are sensitive to the aqueous phase pH for both systems. The adsorption kinetics of the indigenous surfactants and myristic acid could be well fitted with the monoexponential model, and the time constants obtained in this manner indicates that reorganization of the indigenous surfactants and myristic acid at the w/o interface are pH dependent. The experimental results also indicate that indigenous surfactants in acidic crude oil and myristic acid in dodecane have similar film formation behaviours at the w/o interface for the range of pHs investigated.     

Micellization and solubilization of phospholipids by surfactants

Phospholipids comprise the major component that defines biological membranes. Yet these amphiphilic molecules exist as liquid crystals when they are dispersed in water. Surfactants which form micelles in aqueous solution are quite useful in solubilizing the phospholipids by converting them into mixed micelles. Phospholipids containing short-chain fatty acids have also been chemically synthesized and these form micelles themselves without added surfactants. Below their cmc, monomers of these synthetic phospholipids can be co-micellized with surfactants. The solubilization of natural phospholipids and the micellization of synthetic phospholipids as well as their co-micellization by surfactants will be discussed. Emphasis will be placed on nonionic surfactants where the formation of micelles and mixed micelles with phospholipids has been well studied.