Pulsed Amperometric Detection Waveform Research Articles

Fast pulsed amperometric waveform for miniaturised flow-through electrochemical detection: Application in monitoring graphene oxide reduction

A fast pulsed waveform (2-steps at +400 mV and −400 mV, 10 ms each, 50 Hz cycle repetition) was developed incorporated within a miniaturised EC detector, and used to demonstrate the pulsed amperometric detection (PAD) of hydrazine in a flow-based analytical system. In contrast to standard amperometric detection (AD), a subsequent surface oxide reduction step was applied within the PAD waveform. The PAD applied within a simple flow-injection analysis (FIA) method provided a limit of detection (LOD) just as low as 0.8 nM of hydrazine (RSD 5%, n = 9, linearity r2 = 0.99 for 1 nM-100 μM), which is one order of magnitude lower than the lowest LOD reported todate. Significantly, the LOD was obtained using 5–20 times lower electrode surface area, flow rate, and sample volume, than in previous methods, with 15 times faster cycle repetition frequency than alternative PAD based studies reported in literature. Practical application of the PAD waveform was demonstrated by monitoring the temporal consumption of reducing agents during graphene oxide reduction experiments, separated using chromatographic methods (hydrazine in IC and ascorbic acid in HPLC).

Development of an analytical method for the determination of polyphenolic compounds in vegetable origin samples by liquid chromatography and pulsed amperometric detection at a glassy carbon electrode

A sensitive and accurate method for the determination of polyphenolic compounds in artichoke bract extracts and olive mill wastewaters by liquid chromatography coupled with pulsed amperometric detection at a glassy carbon working electrode was developed. Preliminary experiments were carried out by cyclic voltammetry to investigate the electrochemical behavior of polyphenols under different mobile phase compositions, and to test the detection and cleaning electrode potentials. Chromatographic separations were performed by using a core-shell C18 column, eluted with acetic acid and acetonitrile, by combined concave-linear binary gradients. Under the optimized experimental conditions, a good column efficiency and peak symmetry were observed, also for stereo and positional isomeric compounds. The developed three-step potential waveform for pulsed amperometric detection was successfully applied for the sensitive chromatographic determination of polyphenols in artichoke extracts and olive mill wastewaters. Linearity, precision and sensitivity of the proposed method have been evaluated. A wide linear range of response (up to 20mg/L) has been obtained for all the investigated compounds. Detection and quantification limits in the vegetable origin sample extracts were in the range 0.004–0.6mg/L and 0.01–2mg/L, respectively, while the injection-to-injection repeatability (n=6) ranged from 5 to 13%. The obtained results confirmed the excellent sensitivity of the electrochemical detection, and its suitability for the determination of electroactive polyphenolic compounds at low concentration levels.

Cathodic re-activation of the gold electrode in pulsed electrochemical detection of carbohydrates

A new two-step potential waveform for pulsed amperometric detection (PAD) of carbohydrates at polycrystalline gold working electrode is described. In contrast to standard triple- and quadruple-potential waveforms, in the two-step potential waveform cathodic electrode conditioning/re-activation is applied exclusively. Waveform consists of cathodic re-activation potential in hydrogen evolution region (from −1.4V to −2.0V vs. Ag/AgCl) and detection potential at +0.2V. The cathodic processes responsible for activation of Au electrode in alkaline medium were characterized by fast scan cyclic voltammetry, chronoamperometry, and chronocoulometry. It was shown that application of the short negative re-activation potential maintains the electrode surface clean and active and completely substitutes oxidative cleaning/activation at potentials higher than +0.3V used in PAD previously. Both desorptive reduction of the AuOHads and hydrogen evolution reaction play a crucial role in effective cleaning/regeneration of the Au electrode in pulsed sequence. The two-step waveform preserves all analytical properties of three- and four-step potential waveforms and does not result in fouling or dissolution of Au electrode surface in a prolonged use. Square wave sequence substantially simplifies pulsed amperometric detection and enables high frequency sampling required for FIA and capillary IC systems.

Pulsed amperometric detection waveform with disposable thin-film platinum working electrodes in high performance liquid chromatography

A new pulsed amperometric waveform is described for electrochemical detection with microfabricated disposable platinum electrodes. Methanesulfonic acid is selected as an eluent and electrolyte for use with platinum working electrodes. The mode of separation is ion exclusion. The optimized conditions make it possible to achieve improved reproducibility not only for alcohols, aldehydes, sulfite, cyanide and sulfide but also for several new types of analytes, such as ketones and sulfoxides. Utilizing an optimized waveform, reproducible results are obtained with relative standard deviations (RSD) of 3.94% or less. A stable performance for up to 2 weeks could be demonstrated for the detection of alcohols during an uninterrupted use of a single disposable platinum electrode. Further improvements are achieved in overall analytical performance, for example, in limits of detection and calibration linearity. Improvement in detection limits comes mainly from a lower background noise. The calibration is linear over two to five orders of magnitude with correlation coefficients greater than 0.996 for all types of analytes.

Pulsed Amperometry for Anti-fouling of Boron-doped Diamond in Electroanalysis of β-Agonists: Application to Flow Injection for Pharmaceutical Analysis

This work presents the construction and application of boron-doped diamond(BDD) thin film electrode as sensor for the determination of three β-agonists, viz.salbutamol, terbutaline and clenbuterol. Although well-known as a chemically inertmaterial, BDD film however shows fouling in detection of these compounds using fixedpotentialmode amperometry. A suitable waveform for pulsed amperometric detection(PAD) was developed and used to determine the agonist compounds. It was seen that thedeveloped PAD significantly refreshed the BDD surface for long-term detection in flowinjection analysis. Linear working ranges were 0.5-100 μM, 1.0-100 μM and 0.5-50 μM forsalbutamol, terbutaline and clenbuterol, respectively. The developed PAD-BDD system wasapplied to successfully determine salbutamol and terbutaline in commercial pharmaceuticalproducts. The methods were validated with a capillary electrophoresis method.

Flow injection analysis of tetracycline in pharmaceutical formulation with pulsed amperometric detection

A flow injection method with pulsed amperometric detection (PAD) was proposed for the determination of tetracycline in pharmaceutical formulations. Tetracycline was also studied at a gold rotating disk electrode with cyclic voltammetry as a function of the pH of supporting electrolyte solution. The well-defined cyclic voltammogram, providing the highest peak current at 1.15 V versus Ag/AgCl, was obtained when using potassium dihydrogen phosphate solution at pH 2. The optimized pulsed amperometric detection conditions were 1150 mV (versus Ag/AgCl) detection potential ( E det) for 600 ms (500 ms delay time and 100 ms integration time), 1600 mV (versus Ag/AgCl) oxidation potential ( E oxd) for 150 ms oxidation time ( t oxd) and 100 mV (versus Ag/AgCl reference electrode) reduction potential ( E red) for 300 ms reactivation time ( t red). The optimized PAD waveform was applied to the determination of tetracycline standard solution and tetracycline in pharmaceutical formulations. The sensitivity of this method was found to be 13.7 μA/mM. The determination of tetracycline in commercially available tablet dosage forms by the proposed method (254.3±9.3 mg per capsule) was comparable to those labeled (250 mg per capsule).

A consideration of electrode polishing prior to application of pulsed amperometric detection

An examination was made of the effect of electrode polishing on the direct pulsed amperometric detection (PAD) and indirect PAD response to penicillin G. The polishing procedure produced a temporary loss of sensitivity for both types of PAD, which over time relaxed back to higher levels. A temporary increase in the electrode kinetics can be observed as well, particularly for a PAD waveform in the crossover region between direct and indirect PAD. In extreme cases, the penicillin G response can undergo a complete polarity reversal. By observing post-polish equilibration times, it was recommended that the direct and indirect PAD user observe 3 and 5 h delay times, respectively, to insure stable electrode response following an electrode polish.

Activated pulsed amperometric detection of cysteine at platinum electrodes in acidic media

AbstractAnodic voltammetric detection of sulfhydryl compounds, represented here by cysteine, at Pt electrodes in acidic media occurs concomitantly with anodic generation of surface oxide. It is speculated that the adsorbed hydroxyl species (PtOH), proposed to be the intermediate product in formation of the inert oxide (PtO), is the source of O‐atoms transferred to the sulfonic acid produced by oxidation of the sulfhydryl moiety. However, as a consequence of this electrocatalytic response mechanism, application of the traditional three‐step waveform for pulsed amperometric detection (PAD) of sulfhydryl compounds is accompanied by a large background signal resulting from PtO formation. To diminish the background signal, the traditional three‐step PAD waveform has been modified by insertion of a brief (100 ms) anodization step prior to the detection step to activate the Ptsurface by the generation of PtOH with minimal conversion to PtO. The subsequent negative step from the activation potential (Eact) to the detection detection potential (Edet < Eact) permits the PtOH to be harvested within the detection mechanism without significant background signal.

Optimization of waveforms for pulsed amperometric detection of carbohydrates based on pulsed voltammetry

Liquid chromatography (LC) with pulsed amperometric detection (PAD) at Au electrodes has gained prominence for analysis of complex mixtures of polyalcohols and carbohydrates. The most commonly used PAD waveform consists of three potentials and four time parameters, all of which can be varied independently but the effects of which are not necessarily mutually exclusive. Choice of potential values in PAD waveforms has traditionally been based on cyclic voltammetry (CV)