Topics - methanol water mixtures

methanol water mixtures Methanol water mixtures are used as polar mobile phases in liquid chromatography. They are normally used with the complementary dispersive (hydrophobic) stationary phases such as the C8 and C18 hydrocarbon bonded phases. The water provides the strong polar interactions but very weak dispersive interactions whereas the methanol, as well as providing polar interactions, also provides dispersive interactions that can compete with the dispersive interactions of the hydrocarbon bonded phase. In general increasing the methanol content of the mixture increases the dispersive character of the mobile phase. However, the interactive character of the methanol water mixtures is complicated by the fact that methanol strongly associates with water. Thus, at high water contents the mobile phase consists of a mixture of water and methanol associated with water. At the other extreme, at high concentrations of methanol, the mixture consists largely of methanol and water associated with methanol. Only at intermediate mixtures does methanol, water and water associated with methanol coexist in the mixture. It follows that eluting character of methanol water mixtures is complicated and, at intermediate concentrations can be considered as a ternary mixture of methanol, water and water associated with methanol.