Solvent polymeric membrane electrodes incorporating p-t-butyl hexaethyl ester and hexaethyl ester calix[6 ]arene as neutral carriers have been constructed for use in caesium selective electrodes. The potentiometric sensing electrodes including 2-nitrophenyloctyl ether as solvent mediator exhibit near-Nernstian behaviour in the range 1x10 M to 1x10 M CsCl. The pattern of selectivity encountered for a range of common interferents is not modified by the inclusion of potassium tetrakis(p-ch!orophenyl)borate as ion-exchanger in the case of the hexaethyl ester although some improvement in sensitivity is obtained in the case of the hexaethyl ester. The hexaethyl ester is superior with respect to rubidium and potassium selectivities, with the coefficients being of the order of 3x10 and 2.7x10 respectively. Both electrodes are relatively stable and responses are essentially complete within seconds. Different types of sodium electrodes have also been constructed using twomeric calixarene ionophores, namely methyl p-t-butylcalix[4]aryl acetate and the methyl tetraketone derivative of p-t-butylcalix[4]arene. The selectivity of both electrodes is similar although discrimination against ammonium ions is improved by a factor of ten in the case of the methyl tetraketone based electrode. The selectivities against lithium, potassium and hydrogen ions are improved in comparison to other commercially available ionophores. Response times, stability, reproducibility and life time characteristics agree well with the requirements made of these devices for clinical applications. On the assessment of a large number of blood plasma samples, the methyl ester tetrameric based electrode exhibits excellent correlation when compared to two hospital based auto-analysers and to flame photometry. The residual standard deviation is typically within 1 to 3 mmol/1 and highly influenced by the dipping method employed for the determination. Optimisation of the selective membrane in the case of methyl tetraketone based electrodes also give excellent results for the analysis of sodium in plasma samples, although in this case correlation with the above mentioned reference methods is higher and the residual standard deviation is lower. The incorporation of the methyl ester calix[4]arene electrode in a flow injection system has proven advantageous in improving both precision and accuracy in comparison to the dipping technique. Solid-state monomeric and polymeric calixarene based electrodes have been constructed and found to exhibit promising features to varying degrees. Thus, platinum coated electrodes based on the methyl tetraketone calix[4]arene gave similar performance to the conventional sort in terms of Nernstian response, selectivity and response time, although the electrodes are less stable. Another chemically modified tetrameric calixarene (monomer VI) has been found to be responsive to potassium ions. Copolymerisation of two monomeric calixarenes with methyl methacrylate carried out have led to non-responsive electrodes while other polymers exhibited sub-Nernstian slopes to sodium and caesium. Amperometric studies have been also carried out to assess the voltammetric behaviour of pipemidic acid. The drug has been investigated by linear sweep, differential pulse and square wave voltammetry at a hanging mercury drop electrode. Two reduction processes were observed in Britton-Robinson buffer in acidic solutions, whereas only one or two processes were observed in alkaline solutions, depending on the pH of the b u ffer employed. Adsorptive effects have been used to accumulate the drug onto the electrode and linear calibration graphs were obtained in the range 2.5x10 to 1x10" M. A simple procedure of extraction has been employed for the determination of pipemidic acid in urine samples.