Sample injector with metering device balancing pressure differences in an intermediate valve state

A sample injector (200) for use in a fluid separation system (10) for separating compounds of a fluidic sample in a mobile phase, the sample injector (200) comprising a switchable valve (202), a sample loop (204) in fluid communication with the valve (202) and configured for receiving the fluidic sample, a metering device (206) in fluid communication with the sample loop (204) and configured for introducing a metered amount of the fluidic sample on the sample loop (204), and a control unit (208) configured forcontrolling switching of the valve (202) to transfer the sample loop (204) between a low pressure state and a high pressure state via an intermediate state and for controlling the metering device (206) during the intermediate state to at least partially equilibrate a pressure difference in the sample loop (204) between the low pressure state and the high pressure state.