Volume 1, Issue 1 of Chromatography Associates technical newsletter. We hope to keep this short and full of information you can use. Our first topic is the use of guard columns and built in guard columns.

Protecting Your Fused Silica Capillary Column From Contamination

GC capillary columns become contaminated by non-volatile, pyrolyzable or very high molecular weight materials during the normal course of use. These materials enter the column during injection and tend to deposit on the first meter of the analytical column. Eventually they build up sufficiently to interact with the analytes of your sample. The chromatographic evidence of this includes tailing peaks, a decrease in response and sometimes a loss of column efficiency. The analyst could reduce the effect by cutting off 1 meter of the analytical column from the inlet end and reinstalling the column in the injector. Unfortunately this could only be done a few times before the continually shortened column lost the efficiency needed for the analysis. Alternatively, the analyst may rinse the column in the backflush mode with an appropriate solvent. However, this will not remove pyrolyzed and insoluble materials. Small amounts of the stationary phase will also be removed by rinsing.

The best protection for the analytical column is to just not get it dirty.

Guard Columns

A guard column is a piece of deactivated but uncoated fused silica capillary (usually the same id as the analytical column) that is installed into the injector and connected to the front of the analytical column. When contamination builds up on the guard column sufficiently to interfere with your analysis you simply cut off a meter of the guard column and reinstall it into the injector. Performance will be restored and the analytical column is not shortened or damaged. The guard column is attached to the analytical column by means of a connector. These connectors have gone through several generations of design with the most common being the fused silica compression type. (see fig. 1) The mechanism for the gas tight seal on the column involves the polyimide coating on the outside of the capillary and the decreasing internal circumference of the connector. The column ends must be scored and cut cleanly and squarely. The column is inserted into the connector and gently pushed in until a snug fit is obtained. Too much force will crush the column end and too little force will allow leaks.

Built In Guard Columns

A more creative approach to the guard column is to incorporate the guard column and analytical column into one continuous piece. This Built In Guard column is an integral part of the column and requires no connection device. If you have been using a 30 meter column, you would now be using a 35 meter column. The first 5 meters on the inlet side of the column would be the BIG (built-in guard column). (see fig. 2) We highly recommend the use of guard columns whenever there is a possibility of column contamination. We also highly recommend the use of the BIG versions especially when there is an absolute necessity to minimize the possibility of oxygen getting into the system ( high column oven temperature and oxygen sensitive (problematic) detectors systems like ECD and MS).

Chromatography Associates BIG Columns

All Chromatography Associates columns may be configured with a BIG. To order simply add the suffix -01 for a 5 meter built in guard and -02 for a 10 meter version. Add the following list pricing to the cost of the analytical column:

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Thanks and happy separations!

Joe and Andy