Disks or Cartridges – Which Should I Use?

Has anyone been setting up their lab to prepare their samples via solid phase extraction and paused to consider whether you should be using SPE disks or SPE cartridges? Don’t be shy – I’ve asked this question on more than one occasion and it is a valid inquiry.  If you are familiar with SPE (check out one of my recent blogs if you need a refresher), you know that the chemistry involved in your application will be the same, as long as you are using the same media (or stationary phase).

The difference lies with how the media is packed – a flat disk or a syringe-shaped cartridge.  Of course, there are other ways to pack the media – 96 well plate, for example – but we are restricting this discussion to disks and cartridges only.  In a cartridge, the media is arranged vertically, to accommodate a narrow syringe shape. To prevent an excess of backpressure as solutions travel along this long pathway, the media must be bound to relatively large particles (illustrated on the left below).  This particle size creates large pathways for the solution to flow through; however, those pathways can break down if solution flows too quickly through the media – we typically call this “breakthrough.” Disks contain media arranged in more of a horizontal layout, to generate a relatively flat disk shape. This arrangement allows small particles to be used without creating excessive backpressure (illustrated on the right, below).  This particle size also reduces the risk of breakthrough, even at higher solution flow rates.

As with any piece of equipment or analytical technique, there are benefits and challenges.  A few of those are listed below.

SPE Cartridges

Benefits

  • Less expensive than disks
  • Compact
  • Easy-to-use and easily adapted to automated SPE systems
  • Minimal solvent volumes used
  • Limited exposure to harsh solvent vapors

Challenges

  • Requires limited sample flow rates – lower sample throughput
  • Cannot be used to process dirty (particle-laden) samples
  • The addition of pre-filters can reduce analyte recovery

SPE Disks

Benefits

  • Designed to handle any sample matrix, regardless of particulate level
  • Can handle higher sample flow rates – high sample throughput
  • Easy-to-use and easily adapted to automated SPE systems
  • Can handle large sample volumes (> 1 L)

Challenges

  • More expensive than cartridges
  • Require the use of larger solvent volumes, compared to cartridges
  • Fewer consumables and accessories are available for custom applications

Following the guidance above, it would seem pretty straightforward when selecting the SPE media for dirty samples – disks are the way to go. For clean samples, however, I typically ask myself “what’s more important for this application – speed or cost?” If maximizing sample throughput is my highest priority, I use disks for my application. If I am trying to minimize my cost per sample, I will likely use cartridges to process my samples.

Which do you use in your laboratory – disk or cartridges?  Let me know in the comments!

 

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