Binary vs. Quaternary: Which Pump is Right for You?

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Courtesy of Waters Corporation

How to decide which chromatography system pump is right for you

Well, you’ve made it this far and I am guessing that you are coming back because I have provided some useful information to help you understand the differences and nuances of a binary versus quaternary solvent manager for a liquid chromatography instrument. This final chapter will help you think of some questions to ask when you are trying to make a decision about which pump to buy, or which system you would like to implement in the lab.

Which pump is right for my application?

Well, that depends… didn’t I say I would say that a lot in my previous blog on detectors? There are a lot of questions you should ask yourself before making a decision, and here are a few of them:

  • How do I want to prepare my mobile phase?
    1. Premix – If your lab or preference is to use premixed mobile phases or have the mobile phases defined by a pre-existing method, a binary pump could be the preferred system. However, if you are using a complicated mobile phase, all that mixing, diluting and pH’ing (I love making up my own words) the mobile phase must be done up front before starting your analysis. This does require that all chemists in the lab prepare the mobile phases in either a correctly or incorrectly consistent manner (it all depends on how GxP is interpreted in your lab).
    2. Dial-a-mix – If your lab runs a variety of methods that uses the same core solvents but in different compositions, a quaternary pump might be the right choice for you. The quaternary allows a chemist to place four (4) pure solvents on the pump, and then have the pump deliver the desired compositions of each of the solvents to create the gradient conditions needed. This can save on costs as well as create efficiencies in the lab, as the chemist will not have to spend excessive time priming the system or throwing out the premade mobile phase when they are done with an analysis.
  • Am I running pre-defined analysis or performing a lot of method development?
    1. Pre-defined analysis – If you know you are performing pre-defined analysis, a binary system can simplify the situation, as you only have two (2) mobile phases to worry about, and you already know what they are, so you do not need the abilities of custom mixing that can be accomplished on a quaternary system. However, a quaternary system can perform the same pre-defined analyses with a little fine tuning. A quaternary can readily mix from 1 to 4 solvents, and you can just load your mobile phase into two (2) of the solvent lines and perform the same analysis (with slight adjustments during method transfer).
    2. Method Development – If your lab does a lot of method development, a quaternary pump is really the best way to go. It allows an individual to load up four (4) different solvents and do an unattended screening of mobile phases. A scientist can load two lines with different organics and two lines with high and low pH aqueous solvents. This allows for quick switching of solvents without having to excessively prime the pumps to remove traces of the old mobile phase. A lot of scientists also purchase column selection options with a quaternary pump to allow for screening columns and mobile phases at the same time.
  • Am I doing high-throughput or screening applications?
    1. If you are planning on doing high-throughput or screening, a binary is definitely the way to go. Due to the lower dwell volume on the system, gradient delay is reduced and column re-equilibration is much faster thus increasing throughput. A side note to this though, is that a quaternary system provides flexibility to allow chemists to use high and low pH as well as a variety of organic solvents. Sometimes a quaternary’s flexibility and versatility can outweigh a binary’s rapid equilibration in screening labs.

Final considerations: Cost and complexity

The pumps of most binary and quaternary systems of a specific vendor use very similar hardware. However, when you look at a binary system there needs to be two pumps, so there is two of everything!! Two sets of tubing, two sets of check valves, and two sets of plunger seals… well at least you only have one mixer! Because of the fact a binary pump has two of everything this means that the binary pump will command a higher price than a quaternary pump. But, remember price shouldn’t dissuade you, in the end you need to evaluate what you want to do with the system and pick the pump that is right for your laboratory.

Another cost consideration to think about is mobile phase usage and disposal. In a binary system if you change mobile phase you have to prime the system to get rid of the old mobile phase. If the mobile phase is dedicated to a specific assay, then you might have to dispose of excess solvent, when it expires, versus if you have pure solvent on the quarternary that can be reused for other analyses without the need of an intensive priming of the solvent lines.

I hope this blog series has provided you with understanding and guidance on some of the differences between a binary and quaternary pump. It is not filled with chromatograms or specific nuances but it gives you a starting point to at least begin to formulate the right questions to then do further research and work with your colleagues and peers to find the right solution to the challenges you are trying to solve.

Chapters in this series on LC system operation:

  1. Gradient formation
  2. Gradient precision vs. gradient accuracy
  3. High pressure mixing vs. low pressure mixing

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