A sample injector is disclosed comprising a switching valve comprising an input port, an aspiration/dispensing port, a loop input port and a loop output port, a pump port and a column port, an aspiration pump connected to the aspiration/dispensing port via a buffer loop for aspirating a sample into the buffer loop when the aspiration/dispensing port is connected to the loop input port, a sample loop connected to the switching valve between the loop input port and the loop output port, for receiving the sample aspirated into the buffer loop when the loop input port is connected to the aspiration/dispensing port, a column connected to the column port, and a pump connected to the pump port, for injecting the sample received into the sample loop into the column when the pump port is connected to the loop output port and the column port is connected to the loop input port.