Manual injection

When using a manual injection, you can only inject 1 sample at a time. A syringe is used to inject the sample into the HPLC instrument, as seen in Figure 1.

Figure 1. This is a sample injector showing where to insert the needle containing sample that will be injected into the HPLC instrument.

Manual injection consists of a rotary valve (also called Rheodyne injector, see Figure 2) with two main positions: "Load" and "Inject". When the valve is in the "Load position", the sample can be introduced in the system with a syringe. The liquid will fill up a loop which contains a fixed constant volume. The excess of sample that was introduced in the system is discarded in a bottle for waste. Then, you can switch the valve to the "Inject position" and the sample contained in the loop will finally be injected into the mobile phase. The main disadvantage of this type of injection is that it is time consuming since you have to inject the samples one by one.

Figure 2. This is a Rheodyne injector with 2 main position: Load and Inject.