An apparatus for diluting a sample in a liquid chromatography system includes a metering pump, a sample needle and a sample valve. One of the sample valve ports is in fluid communication with the first pump port, a second one of the sample valve ports is in fluid communication with the second pump port, and a third one of the sample valve ports is in fluid communication with the sample needle. The sample valve can be configured in a first to conduct a solvent to the first pump port and to fluidically terminate the second pump port, and in a second state in which the sample needle is in fluid communication with the second pump port. A merge valve configurable in different states is in fluid communication with the sample valve. The states of the sample valve and merge valve can be controlled to perform online dilution.