Determination of the interfacial acidity of the functional alkanethiols self-assembly membrane by capacitance measurement

The acid-base equilibrium of self-assembly monolayer(SAM) of mercaptopropionic acid on gold electrode was studied by capacitance titration. The change of capacitance was due to protonation and deprotonation of the modified electrode surface. This method can be used to measure pH value in solution and capacitance of solid/liquid on SAMs surface synchronously. The shift of pK(a) was observed during the experiment as previous reports. The factors that affect the capacitance measurement were discussed in detail.

The channel behavior of gramicidin in mercaptan self-assembled monolayer membrane

The present paper reports the channel behavior of gramicidin in mercaptan self-assembled monolayer on the surface of the gold electrode by using the electrochemical method. The current responses to K+ ions and the electrode potential for the gold electrodes modified with self-assembled mercaptan monolayer incorporating and not incorporating gramicidin D were compared. The results firstly indicated that gramicidin D molecules can be incorporated into the mercaptan monolayer assembled on the surface of the gold electrode and form monovalent ion channel. A mechanism of the phenomenon was proposed.

Application of modified Nafion membrane to the sulfur dioxide gas electrochemical sensor

The electrochemical SO2 sensor worked at the fixed potential and prepared with Nafion membrane as the solid electrolyte was studied. It v as observed that after Nafion membrane, was treated with H2SO4, the water-preserving ability of the membrane was increased. In turn, the performance of the sensor became stable. After lifetime test for 4 months, the performance of the sensor deceased slightly, Thus this kind of sensor may become a gas sensor for the practical application.

Rare earth separation with 1-hexyl-4-ethyloctyl isopropylphosphonic acid extractant

A new extractant 1-hexyl-4-ethyloctyl isopropylphosphonic acid (HHEOIPP or HA) in heptane was employed to extract rare earths from hydrochloric acid medium. The dependence of extraction distribution ratio on equilibrium aqueous pH and the concentration of extractant were investigated. On the basis of slope analysis,it was proposed that two different kinds of extracted species were formed. For rare earth elements (La similar to Ho) the extracted species was LnA(3)(HA)(3) and for heavy rare earth elements (Er similar to Lu) the species was LnClA(2)(HA)(3). The steric hindrance plays an important role in forming the species. The extraction constants and separation factors of the adjacent rare earths were calculated too. Compared with HDEHP and HEH/EHP, HHEOIPP is a valuable extractant with high separation selectivity. The "tetrad effect" between K-ex and atomic number was observed.

Kinetics separation of copper and palladium by sodium hydroxide precipitation and its analytical application

The method of the kinetics separation of copper and palladium by sodium hydroxide precipitation was described. The reaction orders, apparent rate constants, apparent activation energy of the reactions between sodium hydroxide and copper, and palladium were determined, and the introduced error for the determination of palladium with separating copper and-palladium by sodium hydroxide precipitation was calculated, The proposed method has been applied to determine palladium in the aldehyde catalyst with good result.

Separation of phenothiazines in aqueous and non-aqueous capillary electrophoresis

Four phenothiazines, promethazine, dioxypromethazine, chlorpromazine, and trifluoperazine have been separated by capillary electrophoresis using N, N, -dimethylformamide (DMF) as separation medium with UV absorbance detection. High voltage and concentrated buffer were used with small current and low electroosmosis. Good resolution and high column efficiency were obtained. Separation selectivity in DMI; was different from that in water because of the different solvation interactions. The influence of buffer composition on separation selectivities and electroosmosis were also studied.

Electrochemistry and spectroscopy study on the interaction of microperoxidase-11 with lipid membrane

The interaction of microperoxidase-11 (MP11) with cationic lipid vesicles of didodecyldimethylammonium bromide (DDAB) induces an alpha -helical conformation from random coil conformations in solution and this change then makes heme macrocycle more distorted. DDAB-induced MP11 conformations were investigated by cyclic votammetry (CV), circular dichroism (CD) and UV-vis spectrometry. All results indicate that the binding of MP11 in solution to DDAB vesicles and the ordered structure formation are driven by mostly electrostatic interaction between negatively charged residues in the undecapeptide and positively charged lipid headgroups on the membrane surface. Upon binding to DDAB, its half-peak potential was also changed. The mechanism of the interaction between MP11 and DDAB was also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

Ion-channel sensing of ferricyanide anion based on a supported bilayer lipid membrane

Ferricyanide anion has usually been used as a marker of ion-channel sensors. In this work we first found that ferricyanide, itself, can act as a stimulus to regulate the permeability of sBLM prepared from didodecyldimethylammonium bromide (a kind of synthetic lipid) on a GC electrode. We used cyclic voltammetry and a.c. impedance to investigate this phenomenon. The interaction between sBLM and ferricyanide concerns time. Furthermore, we developed a sensor for ferricyanide anion. The ion-channel sensor is highly sensitive. It can detect ferricyanide concentration as low as 5 muM.

Chiral separation of promethazine by capillary electrophoresis with end-column amperometric detection

Sensitive end-column amperometric detection has been successfully coupled to capillary electrophoresis for chiral separation of promethazine, with a carbon fiber microdisk electrode as working electrode. Baseline separation and sensitive detection were achieved under optimum conditions: 0.030 M Na2HPO4 and 0.015 M citric acid at pH = 2.50, 1.0 mM beta -CD, 10 kV separation voltage, and detection potential 1.10 V (vs Ag/AgCl). The numbers of theoretical plates were higher than 700000, and the detection limit was 5 x 10(-8) M. On-line treatment of the electrode has also been studied and discussed.

Electrocatalytic oxidation of ascorbic acid by norepinephrine embedded in lipid cast film at glassy carbon electrode

A stable lipid cast film was made by casting a lipid in chloroform onto a glassy carbon electrode. We imbedded a new mediator norepinephrine into this lipid cast film, which was considered as a biological membrane model. Through electro catalytic oxidation of ascorbic acid by this system, the anodic overpotential was reduced by about 250 mV compared with that obtained at a bare glassy carbon electrode. The electrochemical behavior of norepinephrine in the cast film was controlled by diffusion. The obtained diffusion coefficient of ascorbic acid was 1.87 x 10(-5) cm 2 s(-1). The catalytic current increased linearly with the concentration of ascorbic acid in the range from 0.5 to 10 mM. Using cyclic voltammetry, we obtained two peaks for ascorbic acid and uric acid in the same solution. The separation between the two peaks is about 147 mV. (C) 2001 Elsevier Science Ltd. All rights reserved.

Synthesis of poly(ether ether ketone)s with high content of sodium sulfonate groups as gas dehumidification membrane materials

Sodium sulfonate-functionalized polyether ether ketone)s derived from Bisphenol A with a degree of sulfonation up to 2.0 were synthesized by aromatic nucleophilic polycondensation of various amounts of 5,5-carbonylbis(2-fluorobenzenesulfonate) (1), 4,4'-diflurobenzophenone (2) and Bisphenol A (2). Copolymers showed excellent thermal stability and good mechanical properties. The selectivity of water vapor over nitrogen of membranes prepared from copolymers 3a and 3h was determined to be 3.43 x 10(6) and 1.05 x 10(7), respectively.

Studies on the transport of lanthanides ions through the membrane of human erythrocyte in vitro by ICP-MS

A method was developed for the determination of lanthanum in the cytoplasm of human erythrocytes after they were incubated in lanthanum nitrate or citrate solutions. The lanthanum concentration in the cytoplasm of incubated erythrocytes is much higher than that in normal erythrocytes. It is suggested lanthanum can transport through the membrane of erythrocyte in vitro. Solutions containing chelator are unsuitable to be washing buffer in the investigation.

A new kind of potassium sensor based on capacitance measurement of mimic membrane

A novel type of potassium sensor based on the capacitance change of valinomycin-incorporated bilayer supported on a gold electrode has been developed and characterized. The lipid membrane was Formed by painted method and monitored simultaneously by capacitance variation. The capacitance of the electrode-supported membrane was found to be modulated by different concentrations of K+. Investigating the capacitance change allows a simple and specific technique for the measurement of potassium ion in solution. Especially, the homemade capacitance meter is, to our knowledge, used to monitor the bilayer membrane formation and detect K+ for the first time. It has been proved that this capacitance measurement is a very useful technique because it is simple and sensitive compared to the other methods.

Magnetic microsphere and its use in biochemical separation and analysis

Magnetic microsphere comprises a magnetically responsive metal or metal oxide core surrounded by a polymer shell with active groups. Nowadays, methods of directly coating polymer, monomer polymerazation, impregnation, extrusion and biological synthesis are generally used to prepare magnetic particles. This kind of superparamagnetic microspheres can be attached to chemical, biochemical and biological substances by their active groups, then applying a magnetic field to separate from the media. Preparation and utilization of magnetic microspheres in immunoassay, nucleic acid hybrization assay, gene sequencing, cell isolation, enzyme immoblization, receptor isolation and other Gelds are reviewed with 44 references in this paper. Also, the further development is outlooked.

Separation of phenothiazines using aqueous and nonaqueous capillary electrophoresis

Separations of phenothiazines, promethazine(PZ), dioxypromethazine (OZ), chlorpromazine(CZ), trifluoperazine(TfZ) and thioridazine(TZ) by capillary electrophoresis in water and FA media were carried out and compared. Thus different selectivity and resolution were observed as media varying from water to FA. Migration order was PZ, OZ, CZ and TZ in water but (TZ+PZ), CZ and OZ in FA, when the same buffer, 25 mmol/L Tris and 25 mmol/L citric acid, was used. It also has been observed that pH has great effect on selectivity both in water and FA and a possible explanation was given. Separation efficiency was higher in FA media than in water because of the permission of high voltage applied. For all separations in FA 30 kV was applied, and when 25 mmol/L Tris was used as buffer, current was only 20 mu A and complete separation of TZ, CZ, PZ and OZ was achieved with effencicy higher than 3.5 x 10(5) theoretical plates for all analytes. The high performance of capillary electrophoresis in FA suggests that FA is an excellent media separation.