Joule heating is a limiting factor when separating proteins in capillary zone electrophoresis (CZE). Low conductivity buffers, are required for high-speed separations. We investigated the use of carrier ampholytes (CA) as background electrolytes (BGE) in CZE. We prepared 25 "narrow pH cuts" of wide pH range (3-10) CA mixture in order to know if these fractions were suitable to be used as BGE in CZE. Each fraction was characterised by CZE analysis, giving an idea of its heterogeneity (number and relative abundance of molecular ampholytes). Conductivities and buffering capacities of each fraction have been also measured. Our conclusion is that "narrow pH cuts" of CA might be well suited buffers for electrophoretic separations.