End-point detection of the potentiometric titration of anionic polyelectrolytes using an anionic surfactant-selective plasticized poly (vinyl chloride) membrane electrode and an anionic surfactant as a marker ion

A plasticized poly (vinyl chloride) (PVC) membrane electrode sensitive to dodecylbenzenesulfonate (DBS) ion is applied to the determination of anionic polyelectrolytes such as potassium poly (vinyl sulfate) (PVSK) by potentiometric titration, using a poly (diallyldimethylammonium chloride) (Cat-floc) solution as a titrant. The end-point of the titration is detected as the potential jump of the plasticized PVC membrane electrode caused by decrease in the concentration of DBS ion added to the sample solution as a marker ion, due to the ion association reaction between the DBS ion and Cat-floc. The effects of the concentration of DBS ion, coexisting surfactants and electrolytes in the sample solution and pH of the sample on the degree of the potential jump at the end-point were examined. A linear relationship between the concentration of anionic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 2 × 10^–5 to 4 × 10^–4 N for PVSK, alginate, and carrageenan. Received: 30 April 1998 / Revised: 6 July 1998 / Accepted: 11 August 1998     

End-point detection of the potentiometric titration of anionic polyelectrolytes using an anionic surfactant-selective plasticized poly (vinyl chloride) membrane electrode and an anionic surfactant as a marker ion

A plasticized poly (vinyl chloride) (PVC) membrane electrode sensitive to dodecylbenzenesulfonate (DBS) ion is applied to the determination of anionic polyelectrolytes such as potassium poly (vinyl sulfate) (PVSK) by potentiometric titration, using a poly (diallyldimethylammonium chloride) (Cat-floc) solution as a titrant. The end-point of the titration is detected as the potential jump of the plasticized PVC membrane electrode caused by decrease in the concentration of DBS ion added to the sample solution as a marker ion, due to the ion association reaction between the DBS ion and Cat-floc. The effects of the concentration of DBS ion, coexisting surfactants and electrolytes in the sample solution and pH of the sample on the degree of the potential jump at the end-point were examined. A linear relationship between the concentration of anionic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 2 × 10^–5 to 4 × 10^–4 N for PVSK, alginate, and carrageenan.     

Determination of cationic polyelectrolytes using a photometric titration with crystal violet as a color indicator

The reaction of the cationic dye, crystal violet (CV) with the anionic polyelectrolytes such as potassium poly (vinyl sulfate) (PVSK) results in a decrease of the absorbance of CV at the maximum absorption wavelength (590 nm). This change of the absorption spectra of the CV has been already applied to the determination of anionic polyelectrolytes using flow injection analysis method. In this paper, CV was applied to the indicator for the determination of cationic polyelectrolytes such as poly (diallyldimethylammonium chloride) (Cat-floc) by photometric titration, using a PVSK solution as a titrant. The end-point of the titration is detected as the break point of the titration curve. A linear relationship between the concentration of cationic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 0 to 5×10⁻⁵ eq. mol dm⁻³ for Cat-floc, glycol chitosan and methylglycol chitosan. The effects of the concentration of CV and coexisting electrolytes in the sample solution and the effect of pH of the sample solution on the degree of the change of absorbance at the end-point were also examined.     

Self-assembled monolayer gold electrode for surfactant analysis

A gold electrode coated with a self-assembled monolayer of octane-thiol (SAM/Au) has been used as an amperometric detector for the determination of surfactants. This detector operated in the presence of a high percentage of organic solvent and was adapted to an HPLC System. At the SAM/Au, the electrochemical response of an electroactive tracer (potassium ferricyanide) was completely inhibited, but, in the presence of a cationic surfactant, the electrochemical reduction was progressively restored. In flow injection analysis, using the SAM/Au in an amperometric flow-through detector polarised at 0.0 V vs Ag/AgCl, a linear response (i=f{[surfactant]}) was observed for cationic surfactants e.g. cetylpyridinium chloride in the concentration range 2 × 10⁻⁶–1 × 10⁻³ M. The electrochemical data along with the determination of the ion pair stoichiometry between the redox tracer and the surfactant suggest an electrochemical response related to ion pair formation and governed by electron transfer by tunneling effect. Received: 28 January 1997 / Accepted: 7 March 1997     

Phase behavior and solution properties of sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate in water

Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) is a conjugated anionic surfactant in which a glycerol residue connects with a hydrophilic sodium succinate and dodecanoate. Aqueous micellar phase (W_m), hexagonal (H₁), bicontinuous cubic (V₁), and lamellar (L_α) phases are successively formed with increasing the surfactant concentration in a binary SLGMS-water system. The Krafft point is below 0 °C. The effective cross sectional area per surfactant molecule, a _s, in the H₁ phase is almost constant, 0.5 nm², and the shape of cylindrical micelle is almost unchanged with surfactant concentration. The cmc value of SLGMS measured by means of surface tension, electrical conductivity, and fluorescence probe methods is in the range of 4∼9 × 10⁻⁵ mol/l that is much lower than that of sodium dodecanoate, 2 × 10⁻² mol/l, or SDS, 8 × 10⁻³ mol/l. Hence, it is considered that the polar glycerol part in the SLGMS acts as a hydrophobic part. The solubilization of oil in the SLGMS solution is much higher than that in the SDS solution and this also suggests that the glycerol and succinic units act as lipophilic moieties. Received: 15 June 2000/Accepted: 27 July 2000     

Potentiometric titration of anionic polyelectrolytes using a cationic surfactant solution as a titrant and a titrant-sensitive plasticized poly(vinyl chloride) membrane electrode

A potentiometric titration method for the direct determination of anionic polyelectrolytes using a plasticized poly(vinyl chloride) membrane electrode is described. A cationic surfactant solution is used as titrant. The method is based on ion association between the anionic polyelectrolyte in the sample and the cationic surfactant in the titrant. The end-point is detected as a sharp potential change due to an increase in the concentration of the free cationic surfactant at the equivalence point. The sharpness of the titration curve at the end-point is compared for several cationic surfactants; a solution of stearyltrimethylammonium ion has been found to be superior. Received: 8 October 1996 / Revised: 17 December 1996 / Accepted: 18 December 1996     

Polyelectrolyte complex formation between poly(diallyldimethyl-ammonium chloride) and copolymers of acrylamide and sodium-acrylate

 The interaction between oppositely charged polyelectrolytes, in this study poly(diallyldimethylammonium chloride) (PDADMAC) and copolymers of acrylamide and sodium-acrylate differing in their chain length and charge density parameter (ξ) was investigated in relation to the molar charge ratio of anionic to cationic charges (n ₋/n ₊). The molecular weights of the polyelectrolytes used were 2.9·10⁵g/mol for PDADMAC and for the polyacrylamide copolymers 14 ·10⁶g/mol as well as 5·10⁵g/mol obtained by ultrasonic degradation of the high molecular weight copolymers. The charge density parameters of the polyanions used (ξ ^PR ) varied between 0.14 and 0.64. Complexation between PDADMAC and high molecular weight polyanions leads mainly to macroscopic phase separation whereas the degraded polyanions and PDADMAC formed soluble complexes as well as stable dispersions, if charge excess was available. Precipitates and dispersions were characterized by several methods such as element analysis, thermogravimetry, pyrolysis-GC/MS, PEL titration, ζ-potential measurements, determination of turbidity, particle size measurements and determination of carbon content (TOC).  All precipitated complexes include about 20% water and are of 1:1 stoichiometry concerning ionic binding. Investigations of dispersions confirm 1:1 stoichiometry of complex particles stabilized by excess polyelectrolyte and soluble complexes. It was also found that the particle size can be varied via the charge density parameter of the polyanions used in the range of negative charge excess. Received: 21 June 2001 Accepted: 9 October 2001     

Potentiometric titration of anionic polyelectrolytes using a cationic surfactant solution as a titrant and a titrant-sensitive plasticized poly(vinyl chloride) membrane electrode

A potentiometric titration method for the direct determination of anionic polyelectrolytes using a plasticized poly(vinyl chloride) membrane electrode is described. A cationic surfactant solution is used as titrant. The method is based on ion association between the anionic polyelectrolyte in the sample and the cationic surfactant in the titrant. The end-point is detected as a sharp potential change due to an increase in the concentration of the free cationic surfactant at the equivalence point. The sharpness of the titration curve at the end-point is compared for several cationic surfactants; a solution of stearyltrimethylammonium ion has been found to be superior. Received: 8 October 1996 / Revised: 17 December 1996 / Accepted: 18 December 1996     

A Novel Enhancing Flow-Injection Chemiluminescence Method for the Determination of Glutathione Using the Reaction of Luminol with Hydrogen Peroxide

 A rapid flow-injection method with chemiluminescence (CL) detection is described for the determination of glutathione (GSH). The method is based on the CL reaction of luminol and hydrogen peroxide. GSH can greatly enhance the chemiluminescence intensity in 0.1 mol/L borax–sodium hydroxide buffer solution (pH = 9.7). The maximum CL intensity was directly proportional to the concentration of GSH in the range 3.0 × 10⁻⁷–2.0 × 10⁻⁵ mol/L, and the detection limit was 6.8 × 10⁻⁸ mol/L. The relative standard deviation was 3.4% for 5.0 × 10⁻⁶ mol/L of GSH (n = 11). Received October 23, 2001; accepted June 18, 2002     

Behaviour of cationic polyelectrolytes upon binding of electrolytes: effects of polycation structure, counterions and nature of the solvent

 The effects of polycation structure, counterions and the nature of the solvent on the interaction between low-molecular-weight salts with some cationic polyelectrolytes in water and methanol were investigated. The polyelectrolytes used in this study were cationic polymers with quaternary nitrogen atoms in the backbone with or without a nonpolar side chain (polymer type PCA₅H₁, PCA₅D₁ and PCA₅) or tertiary amine nitrogen atoms in the main chain (polymer type PEGA). LiCl, NaCl, KCl, NaBr, NaI and Na₂SO₄ were used as low-molecular-weight salts. The interaction between polycations and salts was followed by viscometric and conductometric measurements. The study of the interaction of monovalent counterions with cationic polyelectrolytes emphasized an increase in the interaction with the decrease in the radius of the hydrated counterion, both for strong polycations and for weak polycations, suggesting that counterion binding is nonspecific. In the case of SO²⁻ ₄ anions, the Λ_m−c ^1/2 curve passes through a minimum at c _p values between 1 × 10⁻³ and 3 × 10⁻³ unit mol/l; this phenomenon can be explained by the maximum counterion interaction owing to the capacity of the polyvalent counterion to bind two charged groups by intra- or interchain bridges. The investigation of the influence of the polycation structure on the counterion binding indicated an increase in charged group–counterion interactions with a decrease in the nonpolar chain length and an increase in the quaternary ammonium salt group content (charge density) in the chain. The polyelectrolyte with tertiary amine groups in the chain, PEGA, showed, on one hand, a cation adsorption order as K⁺>Na⁺>Li⁺ and, on the other hand, a stronger association between ions and PEGA chains in methanol than in water owing to the poorer solvating effect of methanol on the cations. Received: 20 February 2001 Accepted: 29 June 2001     

Improvement of an old spectrophotometric method for the microdetermination of ascorbic acid by the use of a micellar medium

₃]²⁺. Whereas the initial method is carried out in an aqueous solution, the improved one employs an aqueous micellar medium formed by the cationic surfactant cetylpyridinium bromide (CPBR). The λmax in both methods is the same, i.e. 510 nm. The mean apparent molar absorptivity (ɛ) and Sandell’s sensitivity (Ss) were calculated as ɛ=2.10×10⁴ Lmol^-1 cm^-1 and Ss=8.37 ng cm^-2 for the initial procedure, and ɛ=2.62×10⁴ Lmol^-1 cm^-1 and Ss=6.72 ng cm^-2 for the improved one. The regression line equation for the improved method was: A=1.487×10^-1C −1.415×10^-2 (r=0.9998). The accuracy and the precision of the improved method were investigated and the conclusions were satisfactory. The results obtained for ASCA by both the described method and an official one, were statistically compared by means of the Student’s t-test and by the variance ratio F-test; and no significant difference was observed. Received: 15 January 1996/Revised: 7 March 1996/Accepted: 13 March 1996     

Flow-injection analysis for the determination of total inorganic carbon and total organic carbon in water using the H2O2–luminol–uranine chemiluminescent reaction

In the presence of carbonate and uranine, the chemiluminescent intensity from the reaction of luminol with hydrogen peroxide was dramatically enhanced in a basic medium. Based on this fact and coupled with the technique of flow-injection analysis, a highly sensitive method was developed for the determination of carbonate with a wide linear range. The method provided the determination of carbonate with a wide linear range of 1.0 × 10⁻¹⁰–5.0 × 10⁻⁶ mol L⁻¹ and a low detection limit (S/N = 3) of carbonate of 1.2 × 10⁻¹¹ mol L⁻¹. The average relative standard deviation for 1.0 × 10⁻⁹–9.0 × 10⁻⁷ mol L⁻¹ of carbonate was 3.7% (n = 11). Combined with the wet oxidation of potassium persulfate, the method was applied to the simultaneous determination of total inorganic carbon (TIC) and total organic carbon (TOC) in water. The linear ranges for TIC and TOC were 1.2 × 10⁻⁶–6.0 × 10⁻² mg L⁻¹ and 0.08–30 mg L⁻¹ carbon, respectively. Recoveries of 97.4–106.4% for TIC and 96.0–98.5% for TOC were obtained by adding 5 or 50 mg L⁻¹ of carbon to the water samples. The relative standard deviations (RSDs) were 2.6–4.8% for TIC and 4.6–6.6% for TOC (n = 5). The mechanism of the chemiluminescent reaction was also explored and a reasonable explanation about chemical energy transfer from luminol to uranine was proposed. Figure Chemiluminescence profiles in batch system. 1, Injection of 100 μL of K₂CO₃ into 1.0 mL luminol-1.0 mL H₂O₂ solution; 2-3 and 4-5, Injection in sequence of 100 μL of K₂CO₃ and 100 μL of uranine into 1.0 ml luminol-1.0 mL H₂O₂ solution; C_luminol = 1.0 × 10⁻⁷ mol/L, C_H2O2 = 1.0 × 10⁻⁵ mol/L, C_uranine = 1.0 × 10⁻⁵ mol/L, C_K2CO3 = 1.0 × 10⁻⁷ mol/L except for 4-5 where C_K2CO3 = 1.0 × 10⁻⁴ mol/L     

Voltammetric determination of malachite green in fish samples based on the enhancement effect of anionic surfactant

In this work, an electrochemical method for the determination of malachite green was developed on the basis of enhancement effect of an anionic surfactant: sodium dodecyl benzene sulfonate. It is found that the oxidation peak current of malachite green at carbon paste electrode significantly increases in the presence of low concentration of sodium dodecyl benzene sulfonate in pH 6.5 phosphate buffer, suggesting that sodium dodecyl benzene sulfonate shows obvious enhancement effect for the determination of malachite green. The experimental parameters, such as supporting electrolyte, kind of surfactant, concentration of sodium dodecyl benzene sulfonate and accumulation time, were optimized, and then a sensitive and convenient electrochemical method was proposed for the determination of malachite green. The oxidation peak current is proportional to the concentration of malachite green over the range from 8.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol l⁻¹, and the detection limit is 4.0 × 10⁻⁹ mol l⁻¹ after 5 min of accumulation. Finally, this new method was successfully employed to detect malachite green in fish samples. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 8, pp. 1019–1024. The text was submitted by the authors in English.     

流动电位/胶体滴定法测定聚电解质电荷密度的研究

探讨了应用粒子电荷测定仪的流动电位判定胶体滴定终点的可行性。结果表明流动电位曲线能在样品浓度大于 0 .6× 1 0 - 5mol· L- 1的溶液中准确指示胶体滴定的终点 ,较常用指示剂邻甲胺兰的使用极限浓度低一个数量级。观察到由阳离子聚电质滴定阴离子聚电质能减少盐干扰的现象。叔胺型阳离子淀粉应在酸性下滴定     

A catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances

A simple and fast catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances has been developed. The procedure for chromium determination in the presence of DTPA and nitrates was employed as the initial method. In order to enhance the selectivity vs. Cr(III) the measurements were performed at 40°C. Interference from dissolved organic matter such as humic and fulvic acids was drastically decreased by adding Amberlite XAD-7 resin to the voltammetric cell before the deaeration step. The whole procedure was applied to a single cell, which allowed monitoring of the voltammetric scan. Optimum conditions for removing humic and fulvic acids due to their adsorption on XAD-7 resin were evaluated. The use of XAD-7 resin also minimize interferences from various cationic, anionic, and nonionic surfactants. The calibration graph for Cr(VI) for an accumulation time of 30 s was linear in the range 5 × 10⁻¹⁰ to 5 × 10⁻⁸ mol L⁻¹. The relative standard deviation for determination of Cr(VI) at a concentration of 1 × 10⁻⁸ mol L⁻¹ was 3.5% (n = 5). The detection limit estimated from 3 times the standard deviation for low Cr(VI) concentrations and an accumulation time of 30 s was about 1.3 × 10⁻¹⁰ mol L⁻¹. The proposed method was successfully applied to Cr(VI) determination at trace levels in soil samples.     

Effects of concentration of nonionic surfactant and molecular weight of polymers on the morphology of anisotropic polystyrene/poly(methyl methacrylate) composite particles prepared by solvent evaporation method

The effects of the concentration of polyoxyethylene octylphenyl ether (OP-10) as a nonionic surfactant and the molecular weight of polymers (polystyrene (PS) and poly(methyl methacrylate) (PMMA)) on the morphology of anisotropic PS/PMMA composite particles were investigated. In the case of polymers with lower molecular weight (M _w ≈ 6.0 × 10⁴ g/mol), the PS/PMMA composite particles have dimple, via acorn, to hemispherical shapes along with the increase of the OP-10 concentration. On the other hand, when the polymers have higher molecular weight (M _w ≈ 3.3 × 10⁵ g/mol), the morphology of PS/PMMA composite particles changed from dimple, via hemispherical, to snowman-like structure while the concentration of OP-10 was increased. Furthermore, thermodynamic analysis was first simply made by spreading coefficients, and the results indicated that both the concentration of OP-10 aqueous solution and the molecular weight of polymers were very important to the final morphology of anisotropic composite particles.     

A new Fluorimetric Reagent for Highly Selective and Sensitive Determination of Terbium Ion

 In this work, a new ligand, 2,9-bis[N,N-bis(carboxymethyl)-aminomethyl]-1,10-phenanthroline (BBCAP), was synthesized and used to establish a novel fluorimetric method for the determination of trace amounts of terbium in a binary system. Its luminescence mechanism was studied. The excitation and emission wavelengths are 284 nm and 547 nm, respectively. Other rare-earth metal ions in 100-fold excess caused no interference. The fluorescence intensity was a linear function of the concentration of terbium in the range of 5.0 × 10⁻¹⁰–1.0 × 10⁻⁶ mol/L. The detection limit was 2.0 × 10⁻¹¹ mol/L (n = 12). The standard addition method was used to determine the terbium in a synthetic rare-earth sample with satisfactory results. This method represents a direct, rapid, selective and sensitive analytical procedure with a widely linear range. Received November 29, 2001 Revision February 9, 2002     

Study of the Fluorescence System of Europium–Enoxacin and its Applications

 This paper is the study of the fluorescence enhancement of Eu³⁺-1-ethyl-6-fluoro-4-oxo-7-(1-piperazinyl)-1,8-naphthyridin-3-carbonic acid (enoxacin, EFLX) system by surfactants. It was found that sodium dodecylbenzenesulfonate (SDBS) exhibits great enhancement on the fluorescence of the Eu-EFLX system. The molar ratio is 1:2:1 for Eu:EFLX: SDBS. Under the optimum conditions, the fluorescence intensity is a linear function of europium in the range of 1.0 × 10⁻⁸ ∼ 5.0 × 10⁻⁶ mol/L, the detection limit is 1.0 × 10⁻⁹ mol/L. The application of the Eu-EFLX-SDBS system for the determination of trace europium in rare earth samples gave satisfactory results. Received October 19, 2000. Revision August 10, 2001.     

Determination of Periodate by Fluorescence Quenching of Tetraiodofluorescein

 The fluorometric determination of periodate with tetraiodofluorescein has been developed. Under the optimum conditions responses were linear between 4.0×10⁻⁷ ∼ 1.0 × 10⁻⁵ mol/L of periodate. The detection limit was 1.0 × 10⁻⁷ mol/L corresponding to a signal to noise ratio of 2. The proposed method was applied to the determination of periodate in artificial fresh water and kelp sample with good results. Received March 20, 2001 Revision December 19, 2001     

Simultaneous determination of catechol and hydroquinone based on poly (diallyldimethylammonium chloride) functionalized graphene-modified glassy carbon electrode

Simultaneous determination of catechol (CC) and hydroquinone (HQ) were investigated by voltammetry based on glassy carbon electrode (GCE) modified by poly (diallyldimethylammonium chloride) (PDDA) functionalized graphene (PDDA-G). The modified electrode showed excellent sensitivity and selectivity properties for the two dihydroxybenzene isomers. In 0.1 mol/L phosphate buffer solution (PBS, pH 7.0), the oxidation peak potential difference between CC and HQ was 108 mV, and the peaks on the PDDA-G/GCE were three times as high as the ones on graphene-modified glass carbon electrode. Under optimized conditions, the PDDA-G/GCE showed wide linear behaviors in the range of 1 × 10⁻⁶−4 × 10⁻⁴ mol/L for CC and 1 × 10⁻⁶−5 × 10⁻⁴ mol/L for HQ, with the detection limits 2.0 × 10⁻⁷ mol/L for CC and 2.5 × 10⁻⁷ mol/L for HQ (S/N = 3) in mixture, respectively. Some kinetic parameters, such as the electron transfer number (n), charge transfer coefficient (α), and the apparent heterogeneous electron transfer rate constant (k _s), were calculated. The proposed method was applied to simultaneous determine CC and HQ in real water samples of Yellow River with satisfactory results.