Abstract:The blank response at glassy carbon electrodes in a flow injection system consists of a transient component and a steady state (residual current) component. The transient response is attributed to nonfaradaic current and faradaic current from the oxidation-reduction of electroactive surface functional groups on glassy carbon. The magnitude of the transient response was dependent on the potential applied to the electrode, temperature, ionic strength and pH of the injected sample solution, and independent of the… Show more
“…The reason for this asymmetry is not understood at present. Similar signal profiles have been observed for electroinactive ions at surface-modified electrodes − and at glassy carbon. , 3 Current response for the injection of pH 5.0, 6.0, 8.0, and 9.0 phosphate buffer solutions (constant ionic strength) to a background of phosphate buffer at pH 7.0.…”
Section: Resultssupporting
confidence: 66%
“…This latter effect, important in Nafion, may similarly apply to UHSAFCs. That is, the surface has both distributed fixed charges and noncharged sites. ,, Another consideration is the applied potential, which determines the electrochemical (double-layer) surface charge, depending on the potential of zero surface charge. , A decision was made to conduct the ion partitioning experiments at an applied potential that resulted in a “background” current at or close to zero. This minimized or eliminated any faradaic processes due to the electrode itself.…”
Charge-selective electrochemistry was previously shown to occur at high surface area carbon fibers that were produced by fracturing the outer periphery with anodic current or positive potential. The cyclic voltammetric behavior of electroactive species observed at these fibers exhibited a distinct pH dependence related to the protonation/deprotonation of oxygen-containing functional groups at the surface of the carbon fiber. In this paper, electrochemical flow injection analysis (EC-FIA) is used to probe ion partitioning in to and out of the interior microstructure of the treated carbon fiber, for both electroactive and electroinactive species. It was found that the extent of partitioning was the result of both ion charge and hydrated ionic radius, in addition to the level of fracture. It was further observed that the direction of movement for an injected ionic species could be controlled relative to the ion concentration, the pH of the carrier solution, or both. EC-FIA allowed the simultaneous observation of current due to ion movement and that due to electron transfer to a redox-active species. The results presented are consistent with a model in which fixed negatively charged sites in the interior of fractured fibers govern ion partitioning with positively charged ions in the carrier solution, with counterions located in the interior "free" volume.
“…The reason for this asymmetry is not understood at present. Similar signal profiles have been observed for electroinactive ions at surface-modified electrodes − and at glassy carbon. , 3 Current response for the injection of pH 5.0, 6.0, 8.0, and 9.0 phosphate buffer solutions (constant ionic strength) to a background of phosphate buffer at pH 7.0.…”
Section: Resultssupporting
confidence: 66%
“…This latter effect, important in Nafion, may similarly apply to UHSAFCs. That is, the surface has both distributed fixed charges and noncharged sites. ,, Another consideration is the applied potential, which determines the electrochemical (double-layer) surface charge, depending on the potential of zero surface charge. , A decision was made to conduct the ion partitioning experiments at an applied potential that resulted in a “background” current at or close to zero. This minimized or eliminated any faradaic processes due to the electrode itself.…”
Charge-selective electrochemistry was previously shown to occur at high surface area carbon fibers that were produced by fracturing the outer periphery with anodic current or positive potential. The cyclic voltammetric behavior of electroactive species observed at these fibers exhibited a distinct pH dependence related to the protonation/deprotonation of oxygen-containing functional groups at the surface of the carbon fiber. In this paper, electrochemical flow injection analysis (EC-FIA) is used to probe ion partitioning in to and out of the interior microstructure of the treated carbon fiber, for both electroactive and electroinactive species. It was found that the extent of partitioning was the result of both ion charge and hydrated ionic radius, in addition to the level of fracture. It was further observed that the direction of movement for an injected ionic species could be controlled relative to the ion concentration, the pH of the carrier solution, or both. EC-FIA allowed the simultaneous observation of current due to ion movement and that due to electron transfer to a redox-active species. The results presented are consistent with a model in which fixed negatively charged sites in the interior of fractured fibers govern ion partitioning with positively charged ions in the carrier solution, with counterions located in the interior "free" volume.
“…15 This technique can be coupled with flow injection analysis (FIA), giving high reproducibility, partial automation and high sample throughput. [16][17][18][19][20] Moreover, electrochemical detection is the first step for the future development of immunosensors in which the antigen-antibody reaction takes place on the surface of the transducer. [21][22][23][24][25][26][27] Alkaline phosphatase (AP) is the most commonly used enzyme label for enzyme linked immunosorbent assay (ELISA).…”
The use of 3,3A,5,5A-tetramethylbenzidine (TMB) as an electrochemical substrate for horseradish peroxidase (HRP) was investigated. HRP activity has been detected using flow injection analysis at a glassy carbon working electrode polarised at +100 mV versus Ag/AgCl in 0.1 mol l 21 citrate-phosphate buffer (pH 5.0). The optimum concentrations were 2 3 10 24 mol l 21 TMB and 10 23 mol l 21 H 2 O 2 . The detection limit obtained after 15 min of incubation was 8.5 3 10 214 mol l 21 HRP with the amperometric method. This limit was lower than that obtained using hydroquinone as HRP substrate and comparable to that with the p-aminophenyl phosphate-alkaline phosphatase system. Better performance was achieved with amperometric than spectrophotometric detection using TMB in a competitive ELISA for rabbit immunoglobulin G as a model analyte.
“…Rather, it seems to have been caused by the charging and discharging processes, as reported earlierl', than by an oxidationreduction of the electroactive surface functional groups suggested for a glassy carbon electrode. 18 The smaller is the dilution ratio, the faster and larger is the decrease in the signal value.…”
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