Indirect determination of surfactants by adsorptive stripping voltammetry

The effect of some anionic, cationic and nonionic surface-active substances on the suppression of adsorptive accumulation of the bis(dimethylglyoximato)nickel(II) complex, Ni(DMG)₂, is described. Competitive adsorption of surfactants can be used to determine surfactants commonly used in commercial detergents. Triton X-100 shows the most pronounced effect on the peak height. The shape of the calibration curve depends on the concentration and on the adsorption potential. Highest sensitivity is obtained when equilibrium between Ni(DMG)² in solution and on the electrode surface is attained rapidly. Under these conditins, the detection limit is 1 μ 1^?1 Triton X-100. Calibrations are linear over 1–2 orders of magnitude.     

Development of an acetylene black–dihexadecyl hydrogen phosphate composite-modified glassy-carbon electrode,and its application in the determination of lovastatin in dosage drug forms

An electrochemical method has been established for the determination of lovastatin (LV). It is based on the enhanced oxidation of lovastatin at a novel acetylene black–dihexadecyl hydrogen phosphate composite-modified glassy-carbon electrode (AB–DHP/GCE) in the presence of Triton X-100. This electrode was prepared by dispersion of acetylene black particles in an aqueous suspension of DHP and the formation of a stable film of the resulting AB–DHP composite on the surface of a glassy carbon electrode (GCE). As a result of modification of the AB–DHP composite, the electrochemical response of lovastatin at GCE was apparently enhanced; this was apparent as amplification of the oxidation current and the negative shift of the oxidation potential. The oxidation current can be further increased in the presence of a trace amount of Triton X-100. The enhanced oxidation of lovastatin at AB–DHP/GCE was due to enlargement of the effective electrode area, catalysis of lovastatin oxidation by AB, and accumulation of lovastatin at the hydrophobic surface of the DHP layer, which would be enhanced by the coherence with Triton X-100. The effects of some working conditions on the oxidation current of lovastatin were tested and the calibration plot was examined. The result showed that the oxidation current was a linear function of lovastatin concentration in the range 2.5×10^–8–1.0×10^–6 mol L^–1 and a low detection limit of 4.0×10^–9 mol L^–1 was obtained under optimum conditions. This electrode system was applied to the determination of lovastatin in dosage drug forms and the results were in accordance with the ultraviolet–visible spectroscopy method.     

Tensammetry with accumulation on the hanging mercury drop electrode : Part 3. The behaviour of triton X-100 in mixtures with PEG-9000

The behaviour of Triton X-100, which can be present in monomeric or associated form, and its mixtures with PEG-9000, which does not undergo association, is described. The tensammetric curve of Triton X-100 alone shows one or two peaks at negative potentials, depending on the concentration of Triton X-100, i.e., on the presence of associated forms. For <2 mg l^?1, there is one broad peak, related to monomers of Triton X-100. The calibration plot for this peak is sigmoidal but its rising section (0.05–0.20 mg l^?1) is approximately linear. The calibration curve of the second, much narrower, peak related to associated forms of Triton X-100, grows parabolically with increasing concentration of Triton X-100. The behaviour of a mixture of PEG-9000 with a larger amount of Triton X-100 is similar to the behaviour of a model mixture of components with sufficiently different properties (e.g., PEG 1500/PEG 9000). The peak for PEG-9000, the stronger surfactant, is relatively less affected by a large amount of Triton X-100. Even this effect can be decreased by using a suitable preconcentration potential (?1.45 V vs. SCE) so that PEG-9000 can be determined in the presence of a 1000-fold amount of Triton X-100. Both peaks of Triton X-100 are greatly decreased by the presence of PEG-9000 and the broad peak can be completely suppressed. Triton X-100 cannot be determined accurately in the presence of unknown amounts of PEG-9000.     

Vergleich von Potentiometrischer Stripping-Analyse und Anodischer Stripping-Voltammetrie in der Flie?injektionsanalyse. St?rungen bei der Bleibestimmung

Summary The interferences caused by inorganic ions, organic anions and Triton X-100 in the determination of lead by flow injection potentiometric and voltammetric stripping analysis at a mercury film electrode were investigated. The experiments were performed in the concentration range of 1–10 mg/l Pb²⁺. For both methods linear calibration plots were obtained in the presence of an excess of nitrate, chloride, perchlorate and sulphate. Iodide strongly interferes due to mercury complexation.Metal ion interference caused by formation of irreversible amalgams (as in the case of codeposition of Ni, Co, Fe and Cr) is avoided by proper choice of deposition potential. No effect of water soluble reduced species, i.e. Fe(II) and Cr(II), on the stripping signals was observed. The presence of acetate, citrate and tartrate does not limit the determination of lead by potentiometric stripping analysis (PSA) but has a marked effect on anodic stripping voltammetric (ASV) signals. No influence of Triton X-100 on the determination of lead by PSA was found. In ASV 10^–3% Triton X-100 diminished the peak current by 15%.

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Herrn Prof. Dr. Rolf Neeb aus Anlaß seines 60. Geburtstags gewidmet     

Determination of the Micellar Properties of Triton X-100 by Voltammetry Method

ABSTRACT

The diffusion coefficient of the micelle, the first CMC and the second CMC of Triton X-100 are determined by cyclic voltammetry without any probe. The first CMC and the second CMC of Triton X-100 are 3.1x lO^?1 and 1.3× 10^?1 respectively. The viscosity of the micelle solution, the micellar aggregation number and the micellar size increase but the diffusion coefficient decreases with Triton X-100 concentration increasing. The mechanism of the electrochemical reaction of Triton X-100 at platinum electrode is deduced by measurements of conductivity, pH and cyclic voltammetry.     

Effects of Triton X-100 on Properties of Hemoglobin and Controlled Release of Drug in Hemoglobin/Ribavirin/H2O System

Effects of Triton X-100 on the properties of hemoglobin (Hb) and on the controlled release of ribavirin were studied using the methods of UV-Vis spectrum, fluorescence spectrum, zeta potential, conductivity, high-performance liquid chromatographic (HPLC), and image morphology in Hb/ribavirin/H₂O system. With the increase of concentration of Triton X-100 in the system, the intrinsic fluorescence intensity, synchronous fluorescence intensity, fluorescence polarization, zeta potential, and morphology of Hb all changed gradually, and the ribavirin located on the Hb surface was dissociated and released out. When the concentration of Triton X-100 was higher than 1×10⁻⁵ mol·L⁻¹, the stronger interaction of Triton X-100 with Hb was predominant. Hb was unfolded and denaturized. A little Triton X-100 can protect Hb from the effects of ribavirin.     

A Study on the Location and Aggregation of Tetrahydrophenylporphyrin with a Single Hexadecyl Chain in Triton X-100 Micelle

The location and aggregation of 5,10,15-tris(4-hydroxyphenyl)-20-(hexadecyloxyphenyl)porphyrin (P) in nonionic polyoxyethylene (9.5) octylphenol (Triton X-100) micelle solutions were studied by means of UV–Vis and fluorescence spectra. P forms premicelle surfactant–porphyrin aggregates when the surfactant concentration is below and approaching the CMC. In Triton X-100 micelle solutions, different types of H-aggregates of P were formed when the concentration of P is higher than 3.9×10^-6?mol?dm^-3. As the bulk pH is changed, a transfer process for the porphyrin moiety in Triton X-100 micelle occurs. In neutral Triton X-100 micelle solutions, P may be located at the inner layer of the micelle; in basic conditions, the porphyrin moiety may transfer to the outer surface of the micelle. The kinetic study of porphyrin complexed with Cu(II) in Triton X-100 micelle solutions shows that the metalation rate could be controlled by changing the pH.     

Determination of surface-active compounds in precipitation studies by ac polarography

The simple procedure is based on measurement of the capacity current of the mercury electrode by a.c. polarography after adsorption of the surfactant. Nonionic surfactants of the Triton-X series were studied in connection with precipitation of colloidal silver iodide. Useful results were achieved in the 10^?4–10^-7 mol dm^?3 range for Triton X-100, X-305 and X-705 by adjusting the sorption time, the type of molecular transport to the electrode and the dilution ratio.     

A direct differential pulse anodic stripping voltammetric method for the determination of thallium in natural waters

A dual direct method for the ultratrace determination of thallium in natural waters by differential pulse anodic stripping voltamrnetry (d.p.a.s.v.) is presented. D.p.a.s.v. at the hanging mercury drop electrode and at the mercury film electrode is used in the concentration ranges 0.5–100 μg Tl l^-1, and 0.01–10 μg Tl l^-1, respectively. Quantification is aided by the technique of standard additions. The response of the method is optimized for typical natural surface water matrices. An intercomparison of thalium determinations performed by the two anodic stripping methods and electrothermal-atomization atomic absorption spectrometry on normal and thallium-spiked surface water samples demonstrates equivalent accuracy within the range where atomic absorption is applicable. The method appears free from serious interferences.     

Removal of humic acid and surfactant interferences in trace metal determinations by differential-pulse anodic stripping voltammetry with use of adsorption and chelate ion-exchanger columns in a flow-injection system

A flow-injection differential-pulse anodic stripping voltammetry (d.p.a.s.v.) method is modified so that interferences from humic acids or surfactants are eliminated. The injected, slightly acidic sample is passed through a silica anion-exchanger column to remove compoundswith a strong tendency to adsorb to the electrode. The sample then passes to a chelate ion-exchange column containing immobilized 8-quinolinol. The metal ions are retained and later eluted with acid into the voltammetric cell. The results show that the interferences from up to 500 mg 1^–1 humic acid or at least 50 mg 1^-1 Triton X-100 can be removed and that the metal ion can be determined in a range similar to that for normal d.p.a.s.v. methods. The complete cycle time for a determination was 12 min.     

Determination of zinc in foods by fluorescence spectroscopy in micellar media

The effect of cationic [cetyltrimethylammonium bromide (CTAB), Zephiramine], non-ionic (Triton X-100, Brij-35) and anionic (sodium lauryl sulphate) surfactant micelles on the fluorescence intensity of the zinc 5,7-dichloro-2-methylquinolin-8-ol chelate is described. In Brij-35 or CTAB micellar media, the fluorescence is about 25 times greater than that obtained in ethanol-water. The relationship between fluorescence intensity and experimental variables was studied in order to develop a procedure for the fluorimetric determination of zinc. Linear calibration graphs were obtained in the ranges 3–100 and 50–400 ng Zn ml^?1. The detection limit is 3 ng ml^?1. The method was successfully applied to the determination of zinc in food samples and drinking waters.     

Cloud point extraction of iron(III) and vanadium(V) using 8-quinolinol derivatives and Triton X-100 and determination of 10(-7)moldm(-3) level iron(III) in riverine water reference by a graphite furnace atomic absorption spectroscopy

The cloud point extraction behavior of iron(III) and vanadium(V) using 8-quinolinol derivatives (HA) such as 8-quinolinol (HQ), 2-methyl-8-quinolinol (HMQ), 5-butyloxymethyl-8-quinolinol (HO₄Q), 5-hexyloxymethyl-8-quinolinol (HO₆Q), and 2-methyl-5-octyloxymethyl-8-quinolinol (HMO₈Q) and Triton X-100 solution was investigated. Iron(III) was extracted with HA and 4% (v/v) Triton X-100 in the pH range of 1.70-5.44. Above pH 4.0, more than 95% of iron(III) was extracted with HQ, HMQ, and HMO₈Q. Vanadium(V) was also extracted with HA and 4% (v/v) Triton X-100 in the pH range of 2.07-5.00, and the extractability increased in the following order of HMQ < HQ < HO₄Q < HO₆Q. The cloud point extraction was applied to the determination of iron(III) in the riverine water reference by a graphite furnace atomic absorption spectroscopy. When 1.25 × 10⁻³ M HMQ and 1% (v/v) Triton X-100 were used, the found values showed a good agreement with the certified ones within the 2% of the R.S.D. Moreover, the effect of an alkyl group on the solubility of 5-alkyloxymethyl-8-quinolinol and 2-methyl-5-alkyloxymethyl-8-quinolinol in 4% (v/v) Triton X-100 at 25 °C was also investigated.     

Micellar-enhanced ultrafiltration of cadmium ions with anionic–nonionic surfactants

Micellar-enhanced ultrafiltration (MEUF), a surfactant-based separation process, is promising in removing multivalent metal ions from aqueous solutions. The micellar-enhanced ultrafiltration of cadmium from aqueous solution was studied in systems of anionic surfactant and mixed anionic/nonionic surfactants. The micelle sizes and zeta potentials were investigated by dynamic light scattering measurements. The effects of feed surfactant concentration, cadmium concentration and the molar ratio of nonionic surfactants to sodium dodecyl sulfate (SDS) on the cadmium removal efficiency, the rejection of SDS and nonionic surfactants and the permeate flux were investigated. The rejection efficiencies of cadmium in the MEUF operation were enhanced with higher SDS concentration and moderate Cd concentration. When SDS concentration was fixed at 3 mM, the optimal ranges of the molar ratios of nonionic surfactants to SDS for the removal of cadmium were 0.4–0.7 for Brij 35 and 0.5–0.7 for Triton X-100, respectively. With the addition of nonionic surfactants, the SDS dosage and the SDS concentration in the permeate were reduced efficiently.     

Reduction of hexavalent chromium at solid electrodes in acidic media: reaction mechanism and analytical applications

The electrochemical detection of hexavalent chromium species was investigated. It was found that Cr(VI) can undergo chemically irreversible reduction in acidic solutions at gold, glassy carbon and boron-doped diamond electrodes. The process was found to be diffusionally controlled at all three electrodes studied. The response obtained at a gold electrode towards the reduction of chromium(VI) produced an electrochemically reversible wave in contrast to those recorded at glassy carbon and boron-doped diamond electrodes. The analytical response of the hexavalent species was studied at gold electrodes in the presence of common environmental interferences: Ni²⁺, Cu²⁺, Fe³⁺, Cr³⁺ and Triton X-100 (surfactant), with an LoD of 4.3 μM obtained in the presence of 5 mM Cr(III).     

Spectrophotometric determination of chlorhexidine with bromocresol green by flow-injection and manual methods

A spectrophotometric study of the chlorhexidine/bromocresol green/Triton X-100 system is reported; at pH 5.3, both 2:1 and 1:1 bromocresol green/chlorhexidine complexes are formed. In the manual spectrophotometric method, Beer's law is obeyed for chlorhexidine concentrations of 2.9–32.2 μg ml^?1 (r.s.d. 0.4–1.3%); the molar absorptivity is 12 500 l mol^?1 cm^?1. In the flow-injection method, the calibration graph is linear for the chlorhexidine range 23.0–83.9 μg ml^?1 (r.s.d. 0.8%); the injection is ca. 60 h^?1. Benzocaine, acetylsalicylic acid, ascorbic acid and sucrose are tolerated at 10^?2?10^?3 M levels. Hibitane 5% was analyzed successfully.     

Determination of residual chlorine in tap water by flow-injection spectrophotometry

The method is based on the redox reaction between 4,4′-tetramethyldiaminothiobenzophenone (thio-Michler's ketone) and chlorine at pH 3.5; 2-methoxyethanol and Triton X-100 are used to keep the reagent in solution. The absorbance of the blue quinoidal product is measured at 640 nm. Linear calibration is obtained for 0.2?1.0 mg l^?1 chlorine. The method is suitable for tap waters.     

Sono-anodic stripping voltammetric determination of cadmium in the presence of surfactant

The effect of applying ultrasound in anodic stripping voltammetry analysis of Cd²⁺ in pH 4.6 buffer containing the surfactant Triton X-100 has been investigated. Manipulation of the horn intensity and the horn/electrode distance was found to reduce the deleterious influence of the surfactant on the height of the cadmium peak. The system has been optimised to take advantage of the in situ cleaning action offered by ultrasound. As a result facile detection of Cd²⁺ (0.05–4 μM) in solutions containing 10 μg/mL Triton X-100 can be achieved without recourse to sample pretreatments or electrode modifications. Received: 17 April 2000 / Revised: 2 June 2000 / /Accepted: 8 June 2000     

Preconcentration procedure using cloud point extraction in the presence of electrolyte for cadmium determination by flame atomic absorption spectrometry

This paper describes a micelle-mediated phase separation in the presence of electrolyte as a preconcentration method for cadmium determination by flame atomic absorption spectrometry (FAAS). Cadmium was complexed with ammonium O,O-diethyldithiophosphate (DDTP) in an acidic medium (0.32 mol l^− 1 HCl) using Triton X-114 as surfactant and quantitatively extracted into a small volume (about 20 μl) of the surfactant-rich phase after centrifugation. The chemical variables that affect the cloud point extraction, such as complexing time (0–20 min), Triton X114 concentration (0.043–0.87% w/v) and complexing agent concentration (0.01–0.1 mol l^− 1), were investigated. The cloud point is formed in the presence of NaCl at room temperature (25 °C), and the electrolyte concentration (0.5–5% w/v) was also investigated. Under optimized conditions, only 8 ml of sample was used in the presence of 0.043% w/v Triton X-114 and 1% (w/v) NaCl. This method permitted limits of detection and quantification of 0.9 μg l^− 1 and 2.9 μg l^− 1 Cd, respectively, and a linear calibration range from 3 to 400 μg l^− 1 Cd. The proposed method was applied to Cd determination in physiological solutions (containing 0.9% (w/v) of NaCl), mineral water, lake water and cigarette samples (tobacco).     

Electrocatalytic performance of cobalt microparticles film-modified platinum disk electrode for amperometric detection of ascorbic acid

Deposited cobalt microparticales (Co-MPs) film onto the platinum disk electrode has been successfully used as a new amperometric sensor for the determination of ascorbic acid (AA). AA is detected by surface catalyzed oxidation involving cobalt(III) oxyhydroxides in alkaline solution. The Co-MPs/Pt electrode exhibits a high electrocatalytic activity toward the AA oxidation. The diffusion coefficient of AA (6.09 × 10⁵ cm²/s) and the catalytic rate constant (k _cat = 6.27 × 10³ M^–1s^–1) have been determined using electrochemical approaches. The amperometric response of the modified electrode is linear against the AA concentration in the range (0.01?0.48 mM). The sensor displays the best activity with a high response signal, a good sensitivity of 74.3 μA/mM, a low detection limit of 2.5 μM (signal/noise = 3) and a fast response time (<3 s). Moreover, the reproducibility, selectivity and applicability of this biosensor are satisfactorily evaluated.     

Cloud point extraction and spectrophotometric determination of codeine in pharmaceutical and biological samples

Cloud point extraction process using non-ionic surfactant, Triton X-114, to extract codeine from aqueous solution was investigated. The method was based on the extraction of codeine and bromothymol blue from acetate buffer media to surfactantrich phase and formed a charge transfer-ion pair complex. The extracted surfactant-rich phase was diluted with ethanol and its absorbance was measured at 430 nm. The effect of different variables such as pH, Triton X-114 concentration, cloud point temperature and time was established. The calibration graph was linear in a wide range of 100–700 ng ml^?1 of codeine with r = 0.998 (n = 7). The detection limit based on three times standard deviation of the blank (3s) was 4.6 ng ml^?1 and relative standard deviation (R.S.D) is 2.15% for 500 ng ml^?1 codeine (n = 5). The proposed method was applied to the determination of codeine in acetaminophen codeine tablets and blood samples.