5. Pump

HPLC pump is at the heart of the HPLC system. It assures an accurate and steady flow of the mobile phase through the column and detector.

HPLC pumps have evolved over the decades. There are three main categories of HPLC Pump Systems:

a) Dual Piston Reciprocating pump

b) Binary pump

c) Quaternary pump

 

A) Dual Piston Reciprocating Pump

Below is an image of a simple reciprocating pump system with ball valves.

Dual reciprocating pump system consists of two of the above pumps working in unison. The advantage is the even flow of the mobile phase.

Because the reciprocating pump does not mix two or more solvents during its operation, it is said to operate in “isocratic” mode. This means that the solvents are first mixed together and then pumped without the ability to change the solvent ratio dynamically.

 

B) Binary Pump System

Binary pump is a newer design. It has a mixing chamber built-in after the pump system – this allows for two separate solvents to be pumped through the two pumps and then mixed prior to being pushed to the column. As a result, the two solvents can be mixed dynamically at changing ratios, allowing for a so-called “gradient” system, where solvents can be mixed in a gradient fashion. This results in increased flexibility of solvent systems and often leads to a better separation of compounds.

 

C) Quaternary Pump System

Quaternary pumps are the latest design where four solvents are independently and dynamically pre-mixed in a mixing valve before entering the pumping system. Quaternary pumps usually have a degasser, which is a vacuum pump that degasses the solvents prior to analysis.

 

Quaternary pump design allows for mixing four solvents giving even better flexibility in analysis design. Many modern HPLC techniques mix 3 solvents dynamically to form a mobile phase gradient. Below is an example of a gradient. This mode of HPLC operation is called “Gradient mode”.