High-Performance Liquid Chromatography: Elution Process

In an HPLC instrument, multiple solvents are stored in solvent reservoirs that facilitate the variation of mobile phase composition and, hence, its polarity.

First, the solvent is filtered and degassed to remove dissolved gases, before it is pumped.

Among high-pressure pumps used in HPLC, the reciprocating pump is the most widely used.

This pump is based on a small piston with two one-way check valves.

When the piston is driven back, the solvent flows in through the inlet valve and is pumped out through an outlet valve during the forward stroke. 

The mobile phase composition is constant in isocratic elution, whereas in gradient elution, it is varied to facilitate separation.

Here, independent binary pumps connected to a mixing chamber regulate the flow rate and polarity of the mobile phase.

Finally, the sample is injected into the flowing mobile phase through a loop injector before it enters the column.