Sample injector for liquid chromatography, particularly for high performance liquid chromatography

A sample injector for liquid chromatography, the sample injector including:

• (a) an injection valve having a waste port, first and second sample loop ports, and first and second high-pressure ports, the first high-pressure port adapted to be connected to a pump and the second high-pressure port adapted to be connected to a chromatography column;
• (b) a sample loop having (i) a first sample loop section operatively connected between the first sample loop port and a pump volume of a sample conveying device, (ii) a second sample loop section operatively connected between the second sample loop port and the pump volume of the sample conveying device, and (iii) an intake arrangement associated with the second sample loop section operable to selectively provide an opening in the second sample loop section to facilitate the intake of a sample fluid into a volume of the second sample loop section;
• (c) a control unit configured to (i) control the injection valve through a sample injection sequence, (ii) control the injection valve through a post sample injection sequence, or (iii) control the injection valve through both the injection sequence and the post sample injection sequence;
• (d) wherein in the sample injection sequence the control unit is configured to (i) place the injection valve in a LOAD position in which the first and second high-pressure ports are connected to one another and isolated from the sample loop, and the second sample loop port is operatively connected to the waste port, and to (ii) after intake of the sample fluid into the volume of the second sample loop section, place the injection valve in a PRESSURE COMPENSATION position in which the first and second sample loop ports are closed so as to facilitate pressurization of the sample loop by the sample conveying device to essentially the operating pressure of the pump, and to (iii) after pressurization of the sample loop, place the injection valve in an INJECT position in which the first high-pressure port is operatively connected to the first sample loop port and the second high-pressure port is operatively connected to the second sample loop port so as to facilitate passage of the sample fluid in the second sample loop section into the second sample loop port toward the second high-pressure port;
• and
• (e) wherein in the post sample injection sequence the control unit is configured to (i) move the injection valve from the INJECT position to the PRESSURE COMPENSATION position so as to facilitate reduction of the pressure in the sample loop to essentially ambient pressure by operation of the sample conveying device, and to (ii) move the injection valve from the PRESSURE COMPENSATION position to the LOAD position after the pressure in the sample loop is reduced.