This work explores the consequences of the reaction between methyltin compounds and inorganic mercury which is thought to occur in the environment. This reaction has considerable environmental importance. The introduction of organotin compounds into the environment may occur as a result of their use in various commercial products, including agricultural biocides. In this case the organotin species is applied directly into the environment. Once they have entered the environment their persistence and fate is of great importance. Some potential reactions, include UV degradation and environmental methylation, these are discussed in Chapter 1, which also includes a discussion of the various analytical techniques that are used for the determination of organotin compounds. Metal speciation has become very important due to its impact on environmental chemistry. Much research has been centered on developing highly efficient analytical techniques that are able to determine rapidly and sensitively the chemical forms of metals in a variety of sample matrices. Capillary Zone Electrophoresis (CZE), one such technique, has been developed as a powerful technique for the rapid and highly efficient separation of metal species. Chapter 2 contains discussion on the theory of CZE along with a section describing the development of a CZE method, and its validation, for the separation of the methyltin chlorides. Chapter 3 contains a preliminary investigation of the reactions of tetramethyltin, which may occur naturally in the environment. This includes an examination of the UV degradation of tetramethyltin and also an investigation of the transmethylation reaction between tetramethyltin and inorganic mercury. The chemistry of trimethyltin chloride, dimethyltin dichloride and methyltin trichloride in the presence of inorganic mercury (II) is described in greater detail in Chapter 4. The parameters of the transmethylation reaction were measured. The reaction was quantified using the CZE method previously developed. Having examined the transmethylation reaction of trimethyltin chloride and inorganic mercury in a liquid medium, the reaction was then examined in the presence of a solid support. Again, CZE was used to measure the product distributions and the kinetic parameters obtained in liquid phase were compared to those obtained in the presence of solid supports. The results are reported in Chapter 5.