Mobile phase reservoir

Figure 1. Mobile phase reservoir consisting of several glass bottle with special caps.

The separation of the analytes takes place due to differences in the interactions with the stationary and mobile phase. The analystes also need to be eluted to reach the end of the column, where it will be detected by the detector. This is the purpose of the mobile phase, to transport the compounds from the injection point to the detector.

Mobile phases consist of a mixture of water and an organic solvent or mixtures of organic solvents. If pH needs to be adjusted, buffer solutions are used instead. This is important when the analytes are sensitive to changes in pH.

The solvents are placed in the mobile phase reservoirs (see Figure 1), which consist of a bottle with a special cap with holes. A tube is placed in these holes connecting the mobile phase reservoir to the column. The mobile phase will travel through these tubes (see Figure 2), into the column and then out to the waste reservoir.

Figure 2. Filter and tubing used to connect the mobile phase reservoir to the HPLC instrument.

Techniques:

There are two types of technique based on the composition of the mobile phase during the experiment.

• Isocratic mode: The composition of the mobile phase stays constant during the run time.
• Gradient elution: The composition of the mobile phase changes with time.