Linhongjia Xiong

Investigation of the optimal transient times for chronoamperometric analysis of diffusion coefficients and concentrations in non-aqueous solvents and ionic liquids

We report the optimal transient times for chronoamperometric experiments in order to simultaneously determine accurate values of concentration (c) and diffusion coefficient (D), or alternatively the number of electrons passed (n) providing c is known. This is achieved by the analysis of the current-time transients resulting from potential steps for the oxidation of ferrocene in acetonitrile and the reduction of cobaltocenium in 1-ethyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide. The analysis is based upon Shoup and Szabo approximation, which has been reported to describe the current response over all time values to within an error of 0.5% [D. Shoup and A. Szabo, Journal of Electroanalytical Chemistry, 1982, 140, 237-245]. The error is quantified through comparing the resulting chronoamperometric data with simulation at all transient times. In addition, an alternative simple approach to the simultaneous determination of nc and D values is proposed by independently investigating the short and long time regimes of chronoamperometric transients. The chronoamperometry of hydrazine is investigated as a multielectron example process.

The indirect electrochemical detection and quantification of DNA through its co-adsorption with anthraquinone monosulphonate on graphitic and multi-walled carbon nanotube screen printed electrodes

The voltammetric responses arising from the co-adsorption of anthraquinone monosulfonate and DNA on to a graphitic electrode are reported. The electrochemical responses of these two species show that the adsorbed species are non-interacting and further they occupy similar sites upon the electrode surface. Consequently it is demonstrated that there is an inverse linear relationship between the surface concentrations of the two species, such that it is possible to indirectly measure the quantity of adsorbed DNA to the electrode through the voltammetric signal of the co-adsorbed anthraquinone monosulfonate. This system is developed through the use of multiwalled carbon nanotube screen-printed electrodes to provide a proof-of-concept analytical methodology via which it is possible to accurately analyse the concentration of a DNA solution, where the limit of detection is shown to be 8.8 μM (equivalent to 5.9 μg/mL).

A simultaneous voltammetric temperature and humidity sensor

We report the simultaneous measurement of temperature and humidity by analysing square wave voltammetric responses of two ferrocene derivatives, decamethylferrocene (DmFc) and 1,2-diferrocenylethylene (bisferrocene, BisFc) in 1-(2-methoxyethyl)-1-methyl-pyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([Moepyrr][FAP]). These two molecules produce three peaks in square wave voltammetry. Through study of the peak potentials of BisFc/BisFc(+) (vs. DmFc/DmFc(+)) and BisFc(+)/BisFc(2+) (vs. DmFc/DmFc(+)) over a temperature range of 298 K to 318 K and humidity range of 1% to 50% using square wave voltammetry, the temperature and humidity dependences of the relative peak potentials were investigated. A reliable method to calculate the humidity and temperature based on the voltammetric experiment is characterised and demonstrated.

Fabrication of disposable gold macrodisc and platinum microband electrodes for use in room-temperature ionic liquids

We report a simple and facile methodology for constructing gold macrodisc and platinum microband electrodes for use in room temperature ionic liquids (RTILs). To validate the use of gold macrodisc electrodes, the voltammetry of Ru(NH3)6(3+) was studied in 0.1 M aqueous KCl. The Randles-Ševčík equation was used to calculate the diffusion coefficient, giving excellent agreement with literature values, suggesting that the gold macrodisc electrode is capable of performing quantitative electroanalysis in aqueous media. Gold macrodisc electrodes were used to study oxidation of ferrocene in N-butyl-N-methylpyrrolidinium bis(fluoromethylsulfonyl)imide ([C4mpyrr][NTf2]) using cyclic voltammetry. The diffusion coefficient of ferrocene, (2.43 ± 0.07) × 10(-11) m(2) s(-1), was obtained. This value is very close to the literature value, indicating good performance of gold electrodes in RTILs. Platinum microband electrodes were tested in 1-propyl-3-methylimidazolium bis-trifluoromethylsulfonylimide ([Pmim][NTf2]) containing decamethylferrocene. Diffusion coefficients and electron transfer rates were obtained by fitting relevant simulations to the experimental data. For comparison, analogous experiments and analyses were performed on a commercial platinum microdisc, where the results obtained from both microdisc and microband agree well, further suggesting that the platinum microband electrode is suitable to be used in RTILs. Finally, gold macrodisc and platinum microband electrodes were used for oxygen detection. Gold macrodisc electrodes were used to find the peak currents of oxygen at each volume percentage analysed. Platinum microband electrodes showed steady-state currents of different volumes of oxygen. These two results are compared which resulted in excellent agreement. This is further confirmed by studying Henrys law constants obtained from both electrodes. The excellent behaviour of these two fabricated electrodes suggests that they are suitable for quantitative measurements and practicable for real world applications.

A hydrogel modified electrode for application as a voltammetric temperature sensor and its use in oxygen detection

We report a hydrogel modified electrode based voltammetric “thermometer” and its application in amperometric oxygen detection so avoiding the need for external temperature monitoring to allow the rigorous measurement of oxygen concentrations. A platinum electrode was modified with a layer of agarose hydrogel containing decamethylferrocene (DmFc) and bisferrocene (BisFc) and a layer of pure ionic liquid containing no ferrocenes as solvent. The differences of the formal potentials between these redox couples were measured using square wave voltammetry and a linear increase of peak separations with temperature was observed so providing a basis for measuring temperature. This system was then applied to the analysis of dry oxygen. The temperature was monitored either by a conventional external thermometer or by the internal voltammetry confined to the agarose hydrogel layer on the electrode surface. The concentration and diffusion coefficient of oxygen were obtained with excellent precision using chronoamperometry over a range of temperatures. Excellent agreement between the two approaches was found showing that the voltammetric redox couples provide a good basis for an in situ “thermometer”.