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Six of the major vitamers and provitamins comprising vitamin A (β-carotene, retinoic acid, retinol, retinyl palmitate, retinyl acetate, and retinal) were examined using voltammetric and controlled potential electrolysis techniques in the aprotic organic solvents acetonitrile and dichloromethane at glassy carbon and platinum electrodes. All of the compounds underwent oxidation and reduction processes and displayed a number of similarities and differences in terms of the number of redox processes and chemical reversibility of the voltammetric responses. The electrochemical properties of the compounds were strongly influenced by the functional groups on the unsaturated phytyl chains (carboxylic acid, alcohol, ester, or aldehyde groups), and not only on the fully conjugated hydrocarbon unit which is common to all forms of vitamin A. The compounds were reduced at potentials between approximately -1.7 and -2.6 vs (Fc/Fc(+))/V (Fc = ferrocene) and oxidized at potentials between approximately +0.2 and +0.7 vs (Fc/Fc(+))/V. The average number of electrons transferred per molecule under long time scale electrolysis experiments were found to vary between 0.4 and 4 electrons depending on the exact molecular structure and experimental conditions.

Pyridinium (the protonated form of pyridine) and related compounds have been proposed to be promising homogenous electrocatalysts in the electrochemical reduction of CO 2 to methanol due to the low overpotential required to achieve faradaic yields of about 20 %, although the percentage yields vary dramatically between different research groups. In this study, experimental conditions were varied during the electrolysis of CO 2 at a platinum electrode in the presence of pyridinium to determine the reasons for the discrepancies in the yields of methanol reported between different research groups. Two other vitamin-based and environmentally friendly nitrogen-containing heterocyclic compounds (nicotinamide and nicotinic acid) which have structural similarities to the promising but toxic pyridine homogeneous electrocatalyst, were also investigated as alternative electrocatalysts for the reduction of CO 2 in aqueous acidic media. Cyclic voltammetry studies suggest that nicotinamide and nicotinic acid (forms of vitamin B 3 ) follow a similar reaction mechanism as pyridine in the reduction of CO 2 . Relatively low faradaic yields of methanol were obtained during controlled potential electrolysis experiments for all the electrocatalysts (0.4-1.9 %) which can be attributed to the low solubility of CO 2 along with the competing hydrogen evolution reaction. It was found that adventitious sources of methanol were responsible for greatly inflating the apparent yields of methanol unless scrupulous care was taken in controlling the experimental conditions. The problem with background methanol is particularly difficult to control due to the electrochemical reactions typically generating products in the parts per million range, considerably lower than normal synthetic reactions.

Gas Chromatography Mass Spectrometry (GC-MS) combined with Thermal Desorption (TD) and solid phase extraction (SPE) methodologies were developed for the quantification and qualification of:• Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated byphenyls (PCBs) bound on airborne particulate matter (PM) (different sizes of 10 and 2.5 μm).• The PAHs and organochlorine pesticides (OCPs) in various water samples collected in lower Himalayas in Bhutan.• The volatile organic sulfur compounds (VOSCs) in air.At a Nanyang Technological University (NTU) rooftop sampling site, airborne particulates