HPLC sample injection valves are typically fixe-loop rotary valves, such as the one shown on the right. The valve has an internal rotor with a series of holes or channels etched through it. These internal channels connect adjacent pairs of external ports. Rotating the valve through 60° connects alternate ports, allowing the flow through the valve to be diverted through the sample loop. This is shown schematically in the interactive animation below, which takes you through the different steps involved in loading the sample loop, making an injection, and running the sample through the column.
In fixed-loop valves, the sample volume is varied by changing the length of tubing used as the loop. Volumes range from a few µL to several hundred µL, depending on the concentration of the analytes in the sample, the size and type of the column, and the application (analytical vs. preparative separations.) Automated injectors and sample changers are also available for use when large numbers of the same type of sample must be run.
Continue the tour:
HPLC: solvents → pump → injector → column → detector
Requires Flash 6 plugin; click on the green buttons that appear at different stages to inject and reload the valve.