Which Pumps Are Used in HPLC?
In order to understand which pumps are used in HPLC, we will first explore why high pressure is needed in HPLC.
Why High Pressure in HPLC?
Over the past 20 years, the trend has been to pack HPLC columns with smaller particles. When I first started at Chrom Tech, most of the columns we sold in the 90s were 5um particle size. Quickly, we saw scientists adopting the smaller 3.5µm particle size when developing new methods, as they were able to increase efficiency and achieve faster chromatography. Fortunately, HPLC pumps could handle the increase in back pressure when going from 5µm to 3.5µm particle sizes.
Historically, HPLC pumps had a typical maximum pressure limit of 6,000 psi (400 bar). Since most labs are trying to increase efficiency and do more work in less time, the trend is continuing for smaller particle sizes in HPLC columns, resulting in more back pressure on the HPLC pump. With the popularity of the sub 2µm particle sizes available for chromatography columns, there became a new need for an Ultra High Pressure HPLC Pump with a maximum pressure rating of 18,000 psi (1200 bar). In essence, the need for high-pressure pumps comes down to the urgency to produce better, faster separations.
What Is a Binary Pump?
Binary Pumps (two solvent gradient formation) are the most popular HPLC pumps on the market. Binary pumps are typically high-pressure mixing pumps that have gradient formation of two solvents. In reversed phase applications, you typically have Solvent A and B. Solvent A is the aqueous/buffered solvent and Solvent B is typically the organic solvent (Acetonitrile, Methanol).
What Is a Quaternary Pump?
Quaternary pumps typically use low-pressure mixing of up to four solvents to form gradients. Since this is low-pressure mixing, solvent degassing or the use of a vacuum degasser is a must. Due to gradient delays inherent in low-pressure mixing, the preferred HPLC pump for most applications is the high-pressure binary mixing pumps.
What Is an Isocratic Pump?
Isocratic Pumps deliver a single solvent for HPLC applications. We find these pumps are used for a variety of metering applications and not limited to just chromatography applications.
When using an isocratic pump for HPLC applications (or other high-performance applications), we recommend Dual-Piston isocratic pumps.
Dual-Piston Isocratic Pumps
Dual-Piston Pumps have two pistons operating in parallel, fully out-of-phase with each other, to produce naturally smooth fluid flow. This is critical for many analytical chromatography applications. Reciprocating piston pumps have the ability to produce consistent volumetric fluid flow under very high-pressure conditions. However, they do not produce pressure. System pressure results from flowing liquid through a resistive circuit (column, tubing, reactor vessel, etc.). These constant-flow pumps produce precise and predictable fluid flow dependent on system resistive pressure and the fluid being pumped.
Single Piston Isocratic Pumps
Single-Piston pumps offer an economical option for metering, dispensing, and general fluid-transfer applications. Single-piston pumps have a ‘rapid-refill’ feature drawing liquid into the pumping chamber quickly, regardless of the metered dispensing rate. This helps minimize flow pulsation. Often, these pumps are configured with a secondary pulse dampener to further smooth fluid flow.
Wetted Flow Path Materials in Chrom Tech HPLC Pumps
Chrom Tech HPLC Pumps are available in various wetted materials. In addition to the primary fluid path material, Stainless Steel, or PEEK (for bio-applications), other wetted materials may include: synthetic ruby, synthetic sapphire, fluoropolymers, and UHMWPE. Stainless Steel fluid paths are most common with broad acceptance in HPLC, processing, and metering applications. Corrosion resistance, high-pressure capability, and general ruggedness make stainless steel the primary choice of materials. PEEK Pumps are used for applications where stainless steel is not chemically compatible.
Chrom Tech offers a range of low-cost, high-pressure liquid chromatography pumps; reach out to Chrom Tech to get more information on isocratic or binary HPLC pumps. Not sure which HPLC pump is best for your application? Reach out to our technical team today—we are here to help!