Baizhao Zeng

Electrochemical behavior and determination of fluphenazine at multi-walled carbon nanotubes/(3-mercaptopropyl)trimethoxysilane bilayer modified gold electrodes.

A novel multi-walled carbon nanotubes/(3-mercaptopropyl)trimethoxysilane (MPS) bilayer modified gold electrode was prepared and used to study the electrochemcial behavior of fluphenazine and determine it. Fluphenazine could effectively accumulate at this electrode and produce two anodic peaks at about 0.78V and 0.93V (versus SCE). The peak at about 0.78V was much higher and sensitive, thus it could be applied to the determination. Various conditions were optimized for practical application. Under the selected conditions (i.e. 0.05M pH 3.5 HCOOH-HCOONa buffer solution, 5mul 1mgml(-1) multi-walled carbon nanotubes for Phi=2.0mm electrode, accumulation at open circuit for 180s), the anodic peak current was linear to fluphenazine concentration in the range from 5x10(-8) to 1.5x10(-5)M with correlation coefficient of 0.9984, the detection limit was 1x10(-8)M. For a 1x10(-5)M fluphenazine solution, the relative standard deviation of peak current was 2.51% (n=8). This method was successfully applied to the determination of fluphenazine in drug samples and the recovery was 96.4-104.4%. The electrode could be easily regenerated and exhibited some selectivity, but some surfactants reduced the peak current greatly. The modified electrode was characterized by alternating current impedance and electrochemical probe.

The influence of surfactants on the electron-transfer reaction at self-assembled thiol monolayers modifying a gold electrode

Monolayer films of thiols with different terminal groups (ue5f8CH3, ue5f8COOH and ue5f8NH2) were prepared on gold electrodes using a self-assembling procedure. Cyclic voltammetry was used to investigate the electron-transfer reaction of potassium ferricyanide at the thiol modified gold electrode in the presence of surfactants. It was found that surfactants show some effects on the electron-transfer reaction at the thiol modified electrode. Cationic surfactants can improve the reversibility of a redox reaction at the thiol modified gold electrodes, while anionic surfactants cause a little inhibition of electron transfer of the redox at both methyl and carboxyl terminal thiol modified gold electrodes. Surfactants can interact with thiol monolayers in different ways, changing the structure and properties of the monolayer film, and can further affect electron transfer at the modified gold electrode.

Voltammetric Response of Glutathione and 3‐Mercaptopropionic Acid Self‐Assembled Monolayer Modified Gold Electrodes to Cu(II)

Glutathione (GSH) self-assembled monolayer (SAM) is prepared on a gold electrode. It has been found that the modified electrode exhibits selective response to cupric ions, and the Cu(II) wave appears at about 0.3u2005V (vs. SCE). Conditions of determination are optimized, including parameters that govern the sensitivity and selectivity of this system. When the gold electrode is modified with the mixture of GSH and 3-mercaptopropionic acid (3MPA), the resulting SAMs modified electrode shows better sensitivity and selectivity for Cu(II) compared with GSH SAM modified gold electrode. Under optimal conditions, the anodic wave height is linear to Cu(II) in the range of ca. 10u2005μM to 0.1u2005mM without preconcentration. The influence of various factors and related mechanism is discussed. The organic monolayer modified electrode is stable and simple to prepare.

Electrochemical study and detection of perphenazine using a gold electrode modified with decanethiol SAM.

A novel method for the determination of perphenazine has been developed. The method is based on the accumulation of perphenazine at a gold electrode modified with decanethiol (DEC) self-assembled monolayer (SAM) and its oxidation at about 0.6 V (vs. saturated calomel electrode (SCE)). Because some coexistent electroactives were blocked and perphenazine was selectively accumulated by the SAM, the electrode exhibited good selectivity and sensitivity. Various conditions were optimized for practical application. Under the selected conditions (i.e. 0.05 M pH 10 sodium borate buffer, accumulation time: 120 s, accumulation potential: -0.4 V, scan rate: 100 mV s(-1)), the anodic stripping peak current was linear to perphenazine concentration in the ranges of 6x10(-9)-5xl0(-7) and 5x10(-7)-5x10(-6) M with correlation coefficients of 0.998 and 0.995, respectively. For a 1.0x10(-6) M perphenazine solution, the relative standard deviation of peak height was 2.3% (n=8). This method was applied to the determination of perphenazine in some drugs and the recovery was 92-101%. In addition, it was found that in the presence of perphenazine, the SAM structure changed a little and more needle holes appeared. However, the SAM could recover the original form when perphenazine and its redox product were removed from the monolayer by repeatedly cycling the electrode in a blank solution for a minute. The modified electrode was characterized by alternating current impedance and electrochemical probe.

ELECTROCHEMICAL DETERMINATION OF COPPER(II) BY GOLD ELECTRODES MODIFIED WITH N-ACETYL-l-CYSTEINE

ABSTRACT Gold electrode modified with N-acetyl-l-cysteine was studied by voltammetry and impedance spectroscopy. It was found that this modified electrode exhibited an excellent sensitivity and selectivity for Cu(II) determination. Conditions of determination were optimized, including parameters that govern the sensitivity and selectivity of this system. Under the optimum conditions, i.e., acetate buffer 0.01 M pH 4.0, modification time 5 h, preconcentration time 7 min, the N-acetyl-l-cysteine modified electrode showed two dynamic ranges of six orders of magnitude (from 10−10 to 10−7 M and from 10−7 to 10−4 M) and the detection limit as low as 1 × 10−10 M. The organic monolayer modified electrode was stable and simple to prepare. The method has been applied to the determination of Cu(II) in a reference material, East Lake water with 0.01 µM Cu(II).

Accumulation and stripping behavior of silver ions at dl-dithiothreitol self-assembled monolayer modified gold electrodes.

Silver ions can be entrapped at the dl-dithiothreitol (HSCH(2)(CHOH)(2)CH(2)SH, DTT) self-assembled monolayer films modified gold electrodes. When the potential was made moving, an anodic peak was observed at about 0.23 V (vs. SCE). When the electrode Au/DTT was modified with dodecyl mercaptan further, more Ag (I) can be accumulated and the peak grows. Conditions, such as solution pH and supporting electrolyte, were optimized for Ag (I) determination. Under the selected conditions, i.e. 0.010 M pH 4.3 potassium hydrogen phthalate, preconcentration time of 5 min at open circuit, the anodic peak height is linear to the concentration of Ag (I) in the small range of 0.6-2.4 muM. The influence of some ions on the determination of Ag (I) was examined. The Br(-) ion makes the peak decrease and NCS(-) makes the peak increase. But the determination is not interfered by 1000-fold Pb(2+), Cd(2+), Hg(2+), Fe(3+), Ni(2+), Co(2+), Cu(2+) and Sn(2+) when EDTA was added into the solution. The mechanism involved was discussed.

The Cathodic Stripping Voltammetric Determination of 6‐Mercaptopurine at a Silver Electrode

Voltammetric studies have been carried out on 6-mercaptopurine (6MP) deposited at a silver electrode. 6MP yields a cathodic stripping signal at about –1.0 V (vs. Ag/AgCl) in pH 7.2 sodium phosphate buffer. Under selected conditions a linear calibration plot was obtained over the range of 0.2–6 μM with a relative standard derivation of 2.9 % for 1 μM 6MP (n = 11, td = 60 s). The voltammetric response of 6MP was dependent on experimental conditions such as solution pH and potential-scan range. Generally 6MP exhibits two adjacent peaks in acidic solutions (pH 9). Cetyltrimethylammonium bromide causes an enhancement of the cathodic stripping peak.

Electrochemical Study of a Polypyrrole Film/Decanethiol Self‐Assembled Monolayer on a Gold Electrode

Cyclic voltammetry and chronoamperometry were used to study the deposition of polypyrrole on a decanethiol self-assembled monolayer modified gold electrode (PPY/SAM/Au). The voltammetric behavior of the PPY/SAM film was investigated in the presence of several different electrolytes. It is found that the SAM shows great influence on the nucleation and growth of the PPY film. The reaction of the SAM and the anions causes the different voltammetric behavior of the polymerization of pyrrole on the modified electrode. Chronoamperometry shows the nucleation and growth of the PPY is initially inhibited but followed by a rapid increase. The SAM also influences electrochemical behavior of PPY film. Experiments show that the SAM can greatly depress the diffusion of anions in the PPY film, and minimize the background capacitance current.

Voltammetric Study of a Cupric Hexacyanoferrate Monolayer Immobilized on Mixed Dodecanethiol-Glutathione Self-Assembled Monolayer Modified Gold Electrode

Mixed dodecanethiol-glutathinone self-assembled monolayers (DDT-GSH) were prepared on a gold electrode and further derivatized to form a monolayer of cupric hexacyanoferrate (CuHCF). Electrochemical behavior of the modified electrode was investigated by cyclic voltammetry. This inorganic monolayer modified electrode is electroactive and its surface concentration is 4.2×10–10u2005molu2005cm–2. It is observed that this modified electrode shows selectivity to potassium ion and exhibits an ideal Nernstian response with a slope of 60u2005mV/decade to potassium ions in the range from 10–2 to 1.0u2005molu2005L–1.

Voltammetric Behavior of 2‐Mercaptopyrimidine at a Silver Electrode

Electrochemical characteristics of 2-mercaptopyrimidine (MPD) have been studied by linear scan voltammetry at a silver disk electrode (AgE). It was found that at appropriate potentials MPD can adsorb on and interact with the electrode to form an insoluble silver salt on the surface. As the potential is made more negative two cathodic peaks appear at −0.66 V and −1.28 V, respectively. The peak at −0.66 V is attributed to the reduction of the sparingly soluble silver compound of MPD, and the other to the reduction of MPD to pyrimidine, which was confirmed by capillary electrophoresis. The deposition/stripping behavior of MPD is discussed and possible mechanisms are proposed. Additionally, the influence of some surfactants and halides on the shape and height of the stripping peaks was determined. It was observed that cationic surfactants such as cetylpyridinium bromide and hexadecyltrimethylammonium bromide can dramatically increase the peak height and decrease the peak width of the peak at −0.66 V.