Capillary electrophoresis is a generic term used to describe separation techniques employing high voltages. In its simplest form, capillary zone electrophoresis (CZE), separations are based on the differential migration of charged analytes under the influence of a high electric field. CZE offers several advantages over other separation techniques, such as high performance liquid chromatography (HPLC). These include higher separation efficiency, enhanced resolution and reduced analysis time. In addition, small injection volumes (nanolitres cf. microlitres for HPLC) and low solvent consumption make CZE an attractive alternative to HPLC. Unfortunately, CZE is not amenable to neutral species, therefore alternative electroseparation methods are employed for neutrals, e.g. capillary electrochromatography (CEC) and micellar electrokinetic chromatography (MEKC), so therefore CZE can be treated as a complementary technique to HPLC.Mass spectrometry (MS) has previously been demonstrated to be a sensitive, selective and near-universal detector. Analytes must be ionised in order to be detected; thus, CZE (which also requires ions) seems an ideal separation technique for combining with MS.CZE/MS interfacing would seem problematic; the linear flow velocity through the capillary is significantly less than that required by appropriate MS ionisation sources (e.g. continuous-flow fast atom bombardment and electrospray). In addition, it is necessary to provide a ground for the separation voltage within the interface. However, interfacing of CZE and MS was first reported in 1987. Since then three distinct interface designs have been developed, co-axial sheath flow, liquid junction and the use of a low flow electrospray (nanospray) interface. Co-axial sheath flow and liquid junction methods serve to increase the overall flow rate of CZE to a suitable level for MS, whereas nanospray is a low flow ionisation technique that accepts similar flow rates to those provided by CZE.The work presented in this thesis details the off-line development of a CZE separation of a pharmaceutical product (cimetidine) and related impurities. The separation was then transferred to mass spectral detection on a commercial triple quadrupole MS instrument employing home-built co-axial sheath flow (electrospray) and nanospray interfaces and the data obtained evaluated. The separation was subsequently transferred to an orthogonal acceleration time-of-flight MS (oa-ToF) for the exact mass determination of the narrow electrophoretic peaks. The feasibility of hydrogen/deuterium exchange via the sheath liquid for CZE/MS has been investigated using model pharmaceutical compounds and preliminary work is presented. An application of CZE/MS for the separation of nicotine and ten of its metabolites has been developed. This method could be further developed into a quantitative assay for nicotine metabolites in biological fluids and suggestions for future work in this area are made.