In this note, a simple way to reduce usage of acetonitrile, of which a world-wide shortage has occurred in 2008, is described.
Columns with 4.6 mm inner diameter (I.D.) are most widely used. Only to decrease column I.D. enables us to save the usage of mobile phase. Scaling down from 4.6 mm I.D. to 4.0 mm I.D. provides 25% reduction of mobile phase, whereas that from 4.6 mm I.D. to 3.0 mm I.D. results in 60% cut.
Downsizing of columns reduces not only running cost but also amount of waste solution. Switching to small I.D. columns is good for the ecology.