Take a guess: which type of pump (binary or quaternary) does the diagram below represent?

Figure 1: Binary High-Pressure Gradient Pump

Some newcomers to liquid chromatography might see four numbered components (1, 2, 3, 4) and assume this is a quaternary pump. In reality, Figure 1 contains only two pumps: Pump A (composed of components 1 and 2) and Pump B (composed of components 3 and 4). Taking Pump A as an example, 1 and 2 act as the main pump and auxiliary pump, respectively, working together to pump the mobile phase in and out. The same logic applies to Pump B. Thus, Figure 1 shows a binary pump, which can use a maximum of two mobile phases simultaneously.

How to Identify a Quaternary Pump?

A quaternary pump consists of only one pump but includes an additional proportioning valve to control the ratio of mobile phases. It is called a "quaternary" pump because it can use up to four mobile phases simultaneously.

Figure 2: Quaternary Low-Pressure Pump

By now, it should be clear that "binary" and "quaternary" do not refer to the number of pumps. Instead, the term "binary" (two) or "quaternary" (four) describes the maximum number of mobile phases that can be used simultaneously: binary pumps support up to 2 mobile phases, while quaternary pumps support up to 4.

What Do "High-Pressure" and "Low-Pressure" Mean?

After understanding the difference between binary and quaternary pumps, you might wonder about the terms "binary high-pressure pump" and "quaternary low-pressure pump." Does "high-pressure" mean binary pumps are more resistant to pressure?

Figure 3: Schematic Diagram of Infusion Pump Structures

(Left: Binary high-pressure pump; Right: Quaternary low-pressure pump)

The labels "high-pressure" and "low-pressure" refer to the location of the mobile phase mixing point: mixing before the pump is "low-pressure," and mixing after the pump is "high-pressure." For binary high-pressure gradient pumps (Figure 3, left), the red dot marks where the two mobile phases (A and B) mix. After being pressurized by their respective pumps, the mobile phases meet at the purge valve and flow to the mixer—this is called high-pressure mixing or post-pump mixing.

You can likely deduce the mixing point for quaternary pumps now. As shown in Figure 3 (right), quaternary pumps mix mobile phases before they enter the pump, so this is called low-pressure mixing or pre-pump mixing.

How to Choose the Right Pump?

After learning about binary high-pressure pumps and quaternary low-pressure pumps, some might think quaternary pumps are better since they can handle four mobile phases. But is that true? Let’s compare their advantages and disadvantages:

In practical applications, choose the infusion pump configuration based on your specific needs and budget.