Guard Column Use

Guards should be used wherever possible in order to protect analytical columns.

Several factors need to be taken into account for optimum performance of the guard system.

• Stationary Phase
• Connection
• Length
• Lifetime

Stationary phase used should ideally be matched to the phase in the analytical column, both in particle size and also in bonded stationary phase.

Connections should be made with a low or nil volume connector such as that seen in the picture above.  If this is not possible then as small a piece of peek tubing should be used as is practically possible.  Peek or any other connection used should be compatible with the thread of the guard and analytical column. Any cuts made in tubing should be symmetrical to avoid the possibility for voids and dead-volume.

The length of the guard should have no discernable effect on the chromatography achieved.  Generally a 10mm guard column will be suitable to protect the analytical column from all but the most contaminated samples.

The i.d. of the guard should be kept as close as possible to the i.d. of the analytical column in order to prevent pressure problems.

It must be remembered that the guard is there to provide protection of the important analytical column, therefore the guard cartridge should be replaced on a much more frequent basis than the analytical column.  This length of time will depend heavily on many factors, such as the quality of the solvents, the sample matrix and the expected number of sample runs. Guard columns should be changed when changes in backpressure or column efficiency are observed.

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