This thesis is divided into two parts. Part A describes the development o f some biosensors based on the immobilisation o f enzymes, tissue, microbes and plant materials in carbon paste. The performance characteristics o f these biocatalytic devices were investigated in both batch and flowing systems for the detection o f neurotransmitters, mono-phenols and glucose using amperometry. A new immobilisation procedure involving the use o f spectroscopic graphite and silicone grease is also described. Anodic Stripping Voltammetry was employed to illustrate the detection o f Pb(II) and Cu(II) at lichen-modified carbon paste electrodes. Continuing the theme o f metal analysis in Part B, comparison o f chromatographic and spectrometric methods is described for the detection o f Fe(III) and Al(III) in soils and clays. Information regarding speciation o f these metals within the matrices o f soils and clays was obtained. Subsequently, a chromatographic method for the separation o f Fe(II) and Fe(III) was investigated involving the use o f an ion-pairing reagent.