Mobile Phase Pressure when mixing Water with Methanol or Acetonitrile

Relationship between the mixing ratio of organic solvent versus pressure

Since the viscosity of methanol is higher than that of acetonitrile, the pressure applied on the column by water/methanol solvents is higher than that of water/acetonitrile solvents. When the mobile phase is changed from a water/acetonitrile solvent to a water/methanol solvent, initially set the solvent to flow at a lower flow rate, and then determine the analysis flow rate while checking the delivery pressure. (Before you use methanol, check the Column's Instruction Manual to ensure it can be used). Furthermore, this will mean increasing the organic solvent ratio more than that of water/acetonitrile solvents, special attention must be paid when the methanol ratio is between 40 and 60% as this will exhibit the highest potential backpressure.