Packed Column information for the beginner

We seem to be getting more calls from first time users of packed columns, so I decided to write this post for these beginners to help them understand the terminology commonly used when describing these products.

 

What is a packed column?

Unlike GC capillary columns, which are referred to as WCOT (Wall Coated Open Tubular), or PLOT (Porous Layered Open Tubular), packed columns are what their name implies, they are packed full of fine particles and not “Open” (like a drinking straw). Because they are packed, they have a much higher pressure drop across the column. This is why they tend to be much shorter in length than a capillary column.

• Packed columns consist of:
  • Tubing
  • Packing
  • End Plugs

• All packed columns contain particles, as mentioned earlier. Particles may be uncoated or coated (with a liquid phase). When the particles are uncoated, they are usually referred to simply as the “packing”.

• When coated, these particles are referred to as a “solid support”. In other words, the particle is the support for the liquid phase.

 

So why would someone use a packed column instead of a capillary column?

• Many older methods, which are still used today, were written using packed columns.
• In many cases, does a better job at separating light gases than capillary columns.
• Less expensive.
• Much more compound capacity. Usually preferred when using a TCD as the detector.
• Many unique selectivity phases/packings not available in capillary dimensions.
• Advantage - Packed:
  • Price
  • Capacity
  • Light gas analysis
  • Unique selectivity phases/packings available
• Advantage - Capillary:
  • Many more theoretical plates (separation power) than a packed column.
  • Can be used with mass spectrometers because of narrower ID’s.
  • Most modern GC’s designed for use with capillary columns.
  • Columns used in most current methods.
• Don’t forget:
  • Make sure you have the necessary fittings for installation.
  • Some sort of flow meter is a necessity.
  • Never, ever cut (trim) a packed column like you would do with a capillary column.  This would most likely cause the bed to collapse.

 

I hope you have found this useful.  For additional information on packed columns, please review our FAQ’s and blog posts.  Thank you.