Relatório de estágio em farmácia comunitária

Relatório de estágio realizado no âmbito do Mestrado Integrado em Ciências Farmacêuticas, apresentado à Faculdade de Farmácia da Universidade de Coimbr

The activity of non-metallic boron-doped diamond electrodes with sub-micron scale heterogeneity and the role of the morphology of sp2 impurities

The electrochemical activity of low boron-doped diamond electrodes prepared by hot filament chemical vapour deposition with varying methane levels in a hydrogen source gas ratio is studied by cyclic voltammetry (CV), Raman spectroscopy and scanning electron microscopy (SEM). The electrochemical response of the electrodes is found to be inconsistent with the electrodes acting as semi-conducting interfaces i.e. no diode like behavior is observable. Hence, on the basis of the presence of sp2 and other non-diamond carbon impurities present in the electrode, the electrochemical response is ascribed as being dominated by these low level impurities masking any response of the boron that may or may not be present. Importantly, near fully reversible voltammetry of the redox probe ruthenium (III) hexamine is recorded and with increasing CH4/H2 ratio used for the preparation, the CV showed the electro-reduction in aqueous solution is found to exhibit a significant decrease in the voltammetric peak-to-peak separation. This changed electrode response is attributed to the altered morphology and dimensions of the non-diamond and graphitic sp2 impurities where the larger impurity domains serve to decrease the electrode resistivity

Improving limits of detection. Microdisc versus microcylinder electrodes

The specific apparent capacitance (Farads per unit geometric area) of commercial carbon microdisc electrodes and in-house fabricated carbon microcylinders is studied through the use of cyclic voltammetry. Home-made microcylinder electrodes exhibit lower specific apparent capacitances and as a result facilitate lower limits of detection. We further demonstrate practically how the electroanalytical limit of the detection of solution phase trace oxygen is significantly improved using such microcylinder electrodes. Finally we show that after the degassing of a solution by nitrogen purging even in the most commonly encountered ‘best’ case scenarios approximately tens of μM of oxygen remain present in the electrochemical cell, unobservable by the commercial microdisc electrodes, but detectable with microcylinder electrodes, testifying to their analytical superiority

Improving limits of detection. Microdisc versus microcylinder electrodes

The specific apparent capacitance (Farads per unit geometric area) of commercial carbon microdisc electrodes and in-house fabricated carbon microcylinders is studied through the use of cyclic voltammetry. Home-made microcylinder electrodes exhibit lower specific apparent capacitances and as a result facilitate lower limits of detection. We further demonstrate practically how the electroanalytical limit of the detection of solution phase trace oxygen is significantly improved using such microcylinder electrodes. Finally we show that after the degassing of a solution by nitrogen purging even in the most commonly encountered ‘best’ case scenarios approximately tens of μM of oxygen remain present in the electrochemical cell, unobservable by the commercial microdisc electrodes, but detectable with microcylinder electrodes, testifying to their analytical superiority

Improving limits of detection. Microdisc versus microcylinder electrodes

The specific apparent capacitance (Farads per unit geometric area) of commercial carbon microdisc electrodes and in-house fabricated carbon microcylinders is studied through the use of cyclic voltammetry. Home-made microcylinder electrodes exhibit lower specific apparent capacitances and as a result facilitate lower limits of detection. We further demonstrate practically how the electroanalytical limit of the detection of solution phase trace oxygen is significantly improved using such microcylinder electrodes. Finally we show that after the degassing of a solution by nitrogen purging even in the most commonly encountered ‘best’ case scenarios approximately tens of μM of oxygen remain present in the electrochemical cell, unobservable by the commercial microdisc electrodes, but detectable with microcylinder electrodes, testifying to their analytical superiority

The activity of non-metallic boron-doped diamond electrodes with sub-micron scale heterogeneity and the role of the morphology of sp2 impurities

The electrochemical activity of low boron-doped diamond electrodes prepared by hot filament chemical vapour deposition with varying methane levels in a hydrogen source gas ratio is studied by cyclic voltammetry (CV), Raman spectroscopy and scanning electron microscopy (SEM). The electrochemical response of the electrodes is found to be inconsistent with the electrodes acting as semi-conducting interfaces i.e. no diode like behavior is observable. Hence, on the basis of the presence of sp2 and other non-diamond carbon impurities present in the electrode, the electrochemical response is ascribed as being dominated by these low level impurities masking any response of the boron that may or may not be present. Importantly, near fully reversible voltammetry of the redox probe ruthenium (III) hexamine is recorded and with increasing CH4/H2 ratio used for the preparation, the CV showed the electro-reduction in aqueous solution is found to exhibit a significant decrease in the voltammetric peak-to-peak separation. This changed electrode response is attributed to the altered morphology and dimensions of the non-diamond and graphitic sp2 impurities where the larger impurity domains serve to decrease the electrode resistivity