A chemical treatment for preparing high purity selectively oxidised SWNTs while preserving optical/electronic properties of the material has been developed. Efficient removal of both metal and carbonaceous impurities has been demonstrated by AFM, TEM, Raman and absorption spectroscopy, while XPS confirmed quantitative conversion of oxidised defects to functionalisable carboxylic acid groups. Furthermore persistence of the characteristic optical properties was confirmed using absorption and NIR photoluminescence spectroscopy, thus indicating preservation of the electronic structure. This chemical treatment thus paves the way for the preparation of high purity, covalently functionalised SWNTs enhancing their potential for use in high-performance optical/electronic applications. A comparison with commonly used purification protocols that utilize nitric acid and sodium hydroxide followed by piranha solution treatments or simple solvent washing is made, highlighting the advantages of the reported method for the production of SWNT starting materials ideal for efficient chemical modifications.