A divert valve allows you to switch portions of the mobile phase to waste before the mass spectrometer. This is particularly important for the portion containing all the un-retained components – many of which are likely to be involatile and contaminate the source. If you really want to keep things clean use a divert valve to divert everything to waste except the compounds of interest. The integrated diverter valve, which is located next to the ion source, can be plumbed in injector mode or diverter mode.