Highly stable voltammetric measurements of phenolic compounds at poly(3-methylthiophene)-coated glassy carbon electrodes

Electrochemical performance of 8-hydroxy-2′-deoxyguanosine and its detection at poly(3-methylthiophene) modified glassy carbon electrode

8-Hydroxy-2'-deoxyguanosine (8-OH-dG) has attracted enormous attention in recent years because it has been acknowledged as a typical biomarker of oxidative DNA damage. In this paper, the electrochemical performance of 8-OH-dG at the poly(3-methylthiophene) (P3MT) modified glassy carbon electrode (GCE) was investigated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The conducting polymer P3MT can effectively decrease the oxidation peak potential of 8-OH-dG and greatly enhance its peak current. In 0.1 M pH 7.0 phosphate buffer solution (PBS), the anodic peak currents of cyclic voltammograms are linear with the 8-OH-dG concentration in two intervals, viz. 0.700-35.0 microM and 35.0-70.0 microM, with the correlative coefficients of 0.9992 and 0.9995, respectively. The detection limit of 8-OH-dG can be estimated to be 0.100 microM (S/N=3). This modified electrode can be used to detect the amount of 8-OH-dG in human urine. Furthermore, the effects of scan rate, pH, and interference of uric acid (UA) for the voltammetric behavior and detection of 8-OH-dG are also discussed. This proposed modified electrode also shows excellent reproducibility and stability that makes it an ideal candidate for amperometric detection of 8-OH-dG in flow injection analysis (FIA) and high performance liquid chromatography (HPLC).

Highly stable electrochemical oxidation of phenolic compounds at carbon ionic liquidelectrode

A carbon ionic liquid electrode (CILE) was used for the investigation of the electrochemical oxidation of phenolic compounds in acidic media using cyclic voltammetry, chronoamperometry and square wave voltammetry techniques. The results indicate that, contrary to many other electrodes, the oxidation of phenolic compounds on CILE is highly stable and does not result in electrode fouling. Cyclic voltammetry showed that phenolic compounds such as phenol, 2,4-dichlorophenol and catechol were oxidized at CILE and remained electroactive after multiple cycles and at high concentrations of phenol. The cyclic voltammetric response of the CILE is very stable with more than 99% of the initial activity remaining after 20 s of stirring of a 0.5 mM solution of phenol.

Highly selective and sensitive determination of dopamine using a Nafion/carbon nanotubes coated poly(3-methylthiophene) modified electrode

A poly(3-methylthiophene) modified glassy carbon electrode coated with Nafion/single-walled carbon nanotubes film was fabricated and used for highly selective and sensitive determination of dopamine. The hybrid film surface of the modified electrode was characterized by scanning electrochemical microscopy (SECM) and the results indicated that the carbon nanotubes were dispersed uniformly on the conductive polymer. The experimental results suggest that the hybrid film modified electrode combining the advantages of poly(3-methylthiophene), carbon nanotubes with Nafion exhibits dramatic electrocatalytic effect on the oxidation of dopamine (DA) and results in a marked enhancement of the current response. In 0.1M phosphate buffer solution (PBS) of pH 7.0, the differential pulse voltammetric (DPV) peak heights are linear with DA concentration in three intervals, viz. 0.020-0.10 microM, 0.10-1.0 microM and 1.0-6.0 microM, with correlation coefficients of 0.9993, 0.9996 and 0.9993, respectively. The detection limit of 5.0 nM DA could be estimated (S/N=3). Moreover, the interferences of ascorbic acid (AA) and uric acid (UC) are effectively diminished. This hybrid film modified electrode can be applied to the determination of DA contents in dopamine hydrochloride injection and human serum. These attractive features provide a potential application for either in vitro measurement of DA in the presence of excess AA and UA or as detectors in flow injection analysis (FIA) and high performance liquid chromatography (HPLC).

Chlorinated Phenol Analysis Using Off-Line Solid-Phase Extraction and Capillary Electrophoresis Coupled with Amperometric Detection and a Boron-Doped Diamond Microelectrode

The analysis of chlorinated phenols (2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol) in river water was accomplished using off-line solid-phase extraction (SPE) and capillary electrophoresis coupled with electrochemical detection. A key to the sensitive, reproducible, and stable detection of these pollutants was the use of a boron-doped diamond microelectrode in the amperometric detection mode. An off-line SPE procedure was utilized to extract and preconcentrate the pollutants prior to separation and detection, with ENVI-Chrom P, a highly cross-linked styrene-divinylbenzene copolymer, being employed as the sorbent. Pollutant recoveries in the 95-100% range with relative standard deviations of 1-4% were achieved. The diamond microelectrode provided a low and stable background current with low peak-to-peak noise. The oxidative detection of the pollutants was accomplished at +1.05 V vs Ag/AgCl without the need for electrode pretreatment. The method was evaluated in terms of the linear dynamic range, sensitivity, limit of quantitation, response precision, and response stability. A reproducible electrode response was observed during multiple injections of the chlorinated phenol solutions with a relative standard deviation of < or =5.4%. Good electrode response stability was observed over many days of continuous use with no significant electrode deactivation or fouling. The separation efficiencies for all six pollutants were greater than 170,000 plates/m. The minimum concentration detectable for all six ranged from 0.02 to 0.2 ppb (S/N > or = 3) using a 250:1 preconcentration factor.

Flow injection amperometric detection of OP nerve agents based on an organophosphorus-hydrolase biosensor detector

A flow-injection system with an organophosphorus-hydrolase (OPH)-biosensor detector has been developed and characterized for the rapid detection of organophosphorus (OP) nerve agents. The enzyme was immobilized onto a thin-film gold detector through a cystamine-glutaraldehyde coupling. Factors influencing the performance were optimized. The resulting flow system offered a fast, sensitive, selective, and stable response. The peak current increased linearly with the concentration of paraoxon and methyl parathion over the 1-10 microM range (sensitivity, 2.29 and 1.04 nA/microM, respectively). The OPH-biosensor flow injection systems offered low detection limits (e.g. 0.1 microM paraoxon), along with a good precision (R.S.D. of 3.6% for 20 successive injections of a 1.0 microM paraoxon solution). The OPH-biosensor flow detector offers great promise for rapid field screening of OP pesticides and nerve agents.

Attenuated total reflection design for in situ FT-IR spectroelectrochemical studies

A versatile spectroelectrochemical apparatus is introduced to study the changes in IR spectra of organic and inorganic compounds upon oxidation or reduction. The design is based on an attenuated total reflection device, which permits the study of a wide spectral range of 16,700 (600 nm)-250 cm(-1), with a small opaque region of 2250-1900 cm(-1). In addition, an IR data collection protocol is introduced to deal with electrochemically nonreversible background signals. This method is tested with ferrocene in acetonitrile; concentrations as low as 1 mM produce results that agree with those in the literature.