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How to Increase the Life Time of your GC Columns? Part VI : Use of Guard Columns

4 Jan 2012

Most of the time the impurities accumulate in the first meter(s) of the column. As the separation process in the capillary starts here, the unwanted interactions that take place will impact immediate the initial band width.  By cutting off the contaminated section, the sample will be introduced in a “clean” section and we obtain similar separation as before..  See fig 1.

 


Fig. 1 Contamination of fused silica columns can be easily removed by cutting-off the first section

 

Many users choose for connecting a guard column in front of the analytical column. The guard column protects the analytical column for contamination, which dramatically increases the column life time. Such a guard column can be trimmed when polluted and eventually be replaced.  Depending on the application  guard columns have a life time of 1 week up to 6 months.

 

Deactivated fused silica tubing can be used as guard column and can purchased per meter of which a defined length. Usually this is 2-5 meters. Disadvantage of cutting parts of the guard column is that the column becomes shorter resulting in change of retention times. If similar length is cut every time, the change of retention becomes predictable. One can also replace the guard entirely when contaminated. This way retention times will always be similar.


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Fig. 2 cutting fused silica: slide in one direction with a ceramic wafer

Bigger challenge is to make the coupling. Best generic results are obtained using a universal PressTight connector. Make a 90-degree cut, (fig 2), by using a ceramic wafer and let the wafer slide one-way along your nail,  wet the column and guard ends with some methanol and push it into the PressTight. By pushing it, an optical “ring” is observed (see fig.3) which is the actual seal made by the polyimide and the surface.

A more elegant solution that eliminates column coupling is to use Integra-Guard columns


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Fig. 3 When making the connecting a "brown" ring must appear.

Integra-Guard Columns

Integrated Guard columns have been first introduced by Restek Corporation around 1990 and have been widely used since. Integrated guard columns are prepared by coating only the last section of the column. This technique is also called “segment” coating.

The advantages are clear. As there is no coupling present we have all the advantages of having “no coupling”..

-          No connection to make, saves lots of time

-          No leaks, improved stability and more accurate data

-          No dead volumes/ activity or thermal mass

-          Easy in maintenance; integrated solution

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Fig. $ Making Integrated guard column: No coupling at all, used widely with Rxi-5Sil MS

Such Integra-Guard columns are typically 5 – 10 m in length and can be made for most standard stationary phases and mostl column diameters. Important is to make a clear mark on the column where the guard column starts. Not every stationary phase can be used as an Integra-Guard solution. The column needs to be deactivated first, followed by a second deposition of the stationary phase layer.  There are different phases that can be manufactured with an Integra-Guard guard column.   Working with integrated guard columns allows the user to use cut a piece periodically from the inlet, without the trouble of making a coupling. Integra guard solutions are avialable for a series of phases.