How HPLC Pumps Work

The first piece of hardware the mobile phase encounters is the pump, which delivers the mobile phase at a flow rate from the autosampler to the column and detector.

System back pressure depends on the pump design and flow rate, mobile phase composition, column dimension, and particle size. Retention time precision is vital to reliable analyte separation, identification, and quantification.

Thanks to years of evolving technology, modern pumps provide pressure up to 1500 bar with excellent flow accuracy and precision. Pulseless delivery of solvent is essential for reproducible measurements.

Most modern HPLC pumps have at least one pair of reciprocating pistons. One piston delivers the flow while the other aspirates the mobile phase at a programmed flow rate.

Piston switching in pumps uses either one motor with a cam drive or multiple linear drive motors – one for each piston. The pistons are either series or parallel, with the latter spreading wear evenly between pump heads at the cost of requiring more check-valves to direct the flow.

In isocratic separations, defined as a constant mobile phase composition throughout the separation, the eluent is either pre-mixed or mixed within the pump.

Alternatively, gradient separations provide varying mobile phase composition throughout the run. An HPLC pump needs one of two things to deliver gradients successfully: a proportioning valve found in low-pressure gradient (LPG) pumps or a second pump block found in high-pressure gradient (HPG) pumps.

• Isocratic pump

  Uses a single pump block and a single solvent inlet line. Ideal for QA/QC analysis with refractive index detection.

• Binary pump

  Utilizes two pump blocks and two solvent inlet lines, enabling high-pressure mixing of two individual solvents. Best used for high-throughput, high-resolution HPLC, UHPLC, or LC-MS applications.

• Quaternary pump

  Uses a single pump block and four solvent inlet lines to mix up to four different solvents. These pumps offer the broadest possible application range with maximum flexibility in mobile phase composition.

• Dual-gradient pump

  Contains two independent ternary-solvent inlet lines or channels, permitting separations simultaneously. Dual-gradient pumps drive increased sample throughput, higher productivity, and switching between applications without re-plumbing.