Study And Application Of The Flow Injection Auto-coupled Biampeorometry Associated With Two Independent Couples

Flow injection classic biamperometry has many outstanding features, including high sensitivity, high selectivity, easy operational procedure and high signal to noise ratio. However, only few reversible couple systems have been used successfully, which prevents the method being more widely used. A novel flow injection irreversible biamperometry has been introduced by associating two independent and inverse irreversible electrode processes. The method not only inherits the conventional advantages of biamperometry for reversible couples but also extends the application scope of biamperometry. Apparently, two random independent and inverse electrode processes, including reversible, irreversible and even dynamical and catalytic couples, can be associated to establish a biamperometric system through the external circuit. The system can be applied to on-line treatment and thus enlarge the application of the biamperometry.In this dissertation, a novel flow injection auto-coupled biamperometry is mainly studied from both theoretical and experimental point of view. Several new ways to construct biamperometric detection scheme have been also proposed, such as the use of two different electrodes, the couples of one reversible and one irreversible electrode process and of two reversible electrode processes. Furthermore, the application of the method has been investigated. This thesis includes the works in the following aspects.(1) Two random independent and inverse electrode processes can be coupled to establish the biamperometric scheme. The technique is therefore called as coupled biamperometry. Coupled biamperometry can be classified into two different categories with regard to the power supply of electrode process. The biamperometry which can run spontaneously under an electromotive force generated between the working and counter electrodes is called auto-coupled biamperometry. On the contrary, the method with the external potential is called external-coupled biamperometry. Flow injection auto-coupled biamperometry is studied both theoretically and experimentally. It is favorable to construct biamperometric system that two independent voltammetriccurves, both the oxidation on anodic scan and the reduction on cathodic scan, are overlapped. The influence of the imposed potential △Ee and the auxiliary reactantconcentration on the method are discussed. The results indicate that high sensitivity and the wide linear range can be achieved by adjusting the impose potential and the auxiliary reactant concentration. The theory is validated by taking iron (III) and iodide system as example.(2) With coupling the oxidation of iodide at a gold electrode and the reduction of permanganate at a platinum electrode, a novel flow injection auto-coupled biamperometric method has been developed for the determination of iodide. In this paper, two different electrodes are used firstly to establish the biamperometric systemand the reversible couple I2/I~- is determined. As an application, the iodine ofcydiodine tablet is determined by the proposed method with the redox reaction of the barbituric acid and iodine.(3) A simple flow-injection auto-coupled biamperometric method for the determination of formaldehyde has been described. The method is based on the elctrocatalytic oxidation of formaldehyde at one platinum electrode, which couples with the reduction of platinum oxide film at another platinum electrode, composing such a biamperometric system as a reversible one. The system can run without any potential difference imposed between two electrodes. The oxidation current of formaldehyde shows linear relationship from l.0x10~-5 to l.0x10~-3 mol I~-1 with a detection limit of 5.6x10~-6 mol I~-1. The method is simple, feasible with satisfactory accuracy and precision and thus, has been applied to the determination of formaldehyde in frozen fish treated with formalin.(4) The voltammetric behavior of trepibutone at a pencil graphite electrode (PGE) is investigated by cyclic and square-wave voltammetry in B-R buffers (pH 1.81-11). Two pairs of well-defined reversible peaks are observed at 1.06 V and 1.24 V over the pH range of 1.81-6.80, which are attributed to the one-electron transfers without proton in two different chemical forms of trepibutone, protonated and non-protonated. The cathodic peaks correspond to a one-electron reduction of the carbonyl of thebenzoyl group, and the anodic peaks correspond to a one-electron oxidation of its free radical. In addition, when the trepibutone concentration is higher, another reversible peak at 0.39-0.26 V is observed in the pH range of 1.81-3.00, corresponding to the transfer of two electrons and two protons, which may be due to the dimer of the trepibutone free radical. Based on the oxidation peak at 1.06 V in B-R buffer (pH 1.81), a square-wave voltammetric method is proposed for the determination of trepibutone. A linear relationship is obtained from 0.24 to 10 fig ml"1 with a detection limit of 20 ng ml"1. The PGE exhibits the best reproducibility and highest sensitivity without any additional procedure for the renewal of the electrode surface. The proposed method is applied to the determination of trepibutone in pharmaceutical formulations.(5) The chemical reactions and kinetics of superoxide anion radical (V with two diphenylamine non-steroidal anti-inflammatory drugs (D-NSAIDs), mefenamic acid (MA) and diclofenac (DCF), are investigated in KH2PO4-Na2B4O7 buffer by using voltammetry. The results show that D-NSAIDs can catalyze the dismutation reaction of O2*', and confirm that diphenylamine, the common moiety of all D-NSAEDs, is the active structure core of D-NSAIDs. The reaction of the catalytic dismutation is zero order for O2', one for D-NSAIDs and one for H+. The apparent rate constants obtained in 20'C are (1.48 ± O.O6)xlO9 L-mol'V1 for MA and (1.18 ± O.O3)xlO8 L-molV1 for DCF, respectively. It is suggested that D-NSAIDs can also chemically scavenge O2'' produced in vitro besides the inhibition of O2" generation by suppressing the activity of cyclooxygenase (COX1 or COX2) and oxidative phosphorylation.