In this example, resveratrol samples were found to produce poor peak shape when a diluent of 100% acetonitrile was used. This is caused by a mismatch of the diluent compared to the mobile phase, which is 80% aqueous. Your diluent should be the same as your mobile phase if possible. If this cannot be achieved, try to make the diluent as close to the mobile phase as you can. Compare the dramatic difference in peak shape obtained simply by altering the diluent.