When working with plasma extracts, we recommend using 50% methanol/50% DI water for washing between injections. Flow rates of 0.5ml/min for 20-30 minutes for a 4.6mm x 250mm column should be sufficient.
When working with LC-MS and biological samples we recommend using 50% methanol/50% Di water as the A solvent. It helps clean the column between runs when biological samples are used. However, for some samples, especially those with a significant amount of lipids, an A solvent of 50:50 water/IPA is recommended.