Rheodyne injector, septum injector, and stop flow are the types of injectors available for HPLC. The working pressure of high-performance liquid chromatography is adequately high so we cannot inject the sample solution into the mobile phase by pouring the syringe through a septum, as an alternative, we introduce the sample in HPLC using a loop injector.
Since it is accurate and reproducible, it does not affect the flow rate and system pressure. Rheodyne injector or loop injector is the most popular injector and is widely used. It is available with a fixed or variable amount of loop, to hold the sample until injected into the column (0.1 – 100 μL).
Nowadays it is also used with the autosampler HPLC systems. It is placed just before the column's inlet. A manual Rheodyne sample injector has two positions, load and inject. In a load position, a sample is loaded into the loop with the help of a syringe. After loading, the sample is injected with the help of manual rotation by switching to the inject position.
Then the sample is flow with the mobile phase in the columns and analyte is separate according to their affinity. If you use a fixed volume injector, only the set volume is passed to the stationary phase and excess is removed.
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