The Sample Valve

Courtesy of Rheodyne Instruments Inc.
Figure 13. The Modified External Loop Sample Valve

After injection, the valve is rotated to position (B) and the mobile phase flushes the sample directly onto the column. The sample is actually forced out of the beginning of the loop so it does not have to flow through the entire length of the loop. This type of injection system is ideally suited for quantitative LC, and is probably by far the most popular injection system in use. Sample valves based on this design is available from a number of manufacturers.