Here we discuss the application of X-ray photoelectron spectroscopy and absorbance–reflectance FT-IR spectroscopy to establish and quantify reactivity relationships between a range of thiophene and pyrrole monomers. In particular we investigate the application of these techniques to the characterisation of conducting polymer materials grown potentiostatically from solutions containing a binary mixture of monomers. Our data have shown that XPS is especially effective in determining polymer composition and the linear correlation between this and solution composition has enabled prescriptive synthesis of copolymer materials from the different combinations of monomers described here. This technique is much more convenient and more reliable than elemental analysis. In contrast we show that FT-IR studies, whilst providing a useful qualitative guide to the functional group content of the material, do not facilitate detailed quantitative analysis because of large intrinsic errors.