HPLC sample injector is a technique used to load and inject the sample solutions into the HPLC system. This method is performed using a specially designed injector which is located before the HPLC column. Three types of injectors are available for HPLC systems. Rheodyne injector or loop injector, septum injector, and stop flow injector.
Some requirements of HPLC injection are:
1. The injection volume must be the same for all samples under one experiment.
2. The samples must be injected without the disturbance system pressure and flow rate of HPLC.
3. The sample should be free from air bubbles.
4. It must be accurate, since the volume of the sample in microliters (0.1 to 100 microliters).
5. The sample solution should be free from any particulate matter.
6. A sample loop in the load position is filled with the sample solution whereas the system is equilibrating. While rotating to the inject point, the sample loop is changed to the high-pressure part of the HPLC system. The flow of the mobile phase delivered by the HPLC pump through the loop and supplies the sample onto the chromatographic column.
- Rheodyne or loop injector as HPLC injection system:
The Rheodyne is the most popular injector in high-performance liquid chromatography since it is accurate, reproducible, and precise sample volume. It has a load and injects mode. The load position permits the loading of the sample solution into the loop with the help of syringes. After the sample is loaded, the manually rotating sample injector allows the sample to flow over a column without any air bubbles, without disturbing the pressure (up to the 6000 psi). and the flow rate of the system.
- Septum Injector:
In this type of injector, the sample is injected by inserting the needle through the rubber septum.
- Stop flow Injector:
The flow of the mobile phase through the HPLC column is stopped while the sample is injected.
- HPLC autosampler injector:
Nowadays modern HPLC systems use autosamplers. The injection valve of autosampler is similar to the manual valve; however, the sample solution is injected by an automatic syringe from the vials in a motorized tray. Generally, autosamplers work by piercing the capped sample vial with a needle and attaching it along the length of the flexible tubing.
The sample is subsequently withdrawn from the vial into the loop by suction and injected in the loop, while the analytes are separated by column and analyzed by the detector (UV/PDA).