How (Not) To Cut Your Capillary Column

There are numerous ways to cut a capillary column. Restek has several tools to accomplish this job. There are sapphire scribes, ceramic scoring wafers, wafers with a handle, and diamond blade column cutters. There are also some tools manufactured by other companies that will cut a capillary column. The choice is typically personal preference. No matter what you choose, a square clean cut is extremely important for good chromatography.

A ceramic scoring wafer is used by the majority of chromatographers, so that will be the focus of my post. Restek’s version is pictured below. Ceramic scoring wafers are readily available from most all chromatography companies, are inexpensive, and are fairly easy to use.

The flat straight edge of the wafer is used to lightly score the fused silica tubing. After scoring the fused silica, slight pressure from one’s finger will break the tubing. If done properly, a nice clean square cute is obtained. 

(S)light pressure and lightly tapping to break the fused silica is stressed in any column cutting instruction guide. If too much pressure is used, you’ll get cuts like the ones in the photos below. These poor cuts have shards of fused silica inside the column and fissures on the side of the column. The shards will create active sites in the column and cause all types of issues. The fissures can perpetuate the break downwards and make the column end brittle. The column on the far right is so badly damaged that it appears to have the pressure from a pair of scissors used to make the cut.

 

If you ever do make a poor cut, make a new cut about 8-12 inches from the end. Cracks can run upwards to 6 inches.  This will help ensure that your new (and good) cut removes any shards and the potential for brittleness caused by a fissure.

As a note, over time a ceramic scoring wafer will dull. As the edge dulls, more pressure will be required to break the fused silica. That excessive pressure will first lead to non-square cuts and eventually to the issues pictured above. When all sides of the wafer start to show signs of being dull, discard and replace it. The same holds true with a sapphire scribe. If you prefer the diamond blade cutter, replace the diamond cutting wheel when you observe poor cuts.

I would like to thank Wendy Henninger, one of our QS Engineers, who provided the detailed photos of the poorly cut columns.