CE-ESI-MS has become a powerful analytical tool capable of simultaneous identification and quantification of many classes of biologically relevant molecules. For studies in metabolomics, CE-ESI-MS offers a unique platform which will allow for the systematic elucidation of unknown metabolites in complex matrices without the need for complex sample preparation steps required with other techniques. In this thesis, a novel theoretical prediction model which will allow the estimation of detector response in ESIMS is outlined. This response model will allow researchers to quantitatively predict relative ionization effiency of compounds based on proposed two-dimensional structures without the need for a purified standard. Another feature of this model is that it can be applied to complex biological samples without the need for off-line sample pretreatment. Also in this thesis, a novel neonatal screening method will be presented which will aid clinical chemists in determining the presence of inborn metabolic disorders. This screening method which aims to compliment current protocols will allow health care professionals to further assess dried blood spot samples by providing simultaneous separation, identification, and quantification of relevant metabolites. This method also offers an alternatives to other protocols in place which are necessary to measure acid labile compounds which cannot be assessed by standard screening techniques. / Thesis / Master of Science (MSc)