Column cutting is an activity that is done many times in the lab. When maintenance is done, often a piece of the column inlet is also cut off. There are an increasing nr of methods, where columns have to be coupled. When using Guard columns, Pre columns (coated guard columns), Retention gaps, transfer tubing or restrictions one need to have a 90 degree end cut to make the optimal connection.
Fig. 1 A good seal in a PressTight requires a good column end-cut
Often the Press Tight connectors are used as they have small dead volume. The seal is made by pushing the fused silica column inside the tapered Press tight. The polyimide outside coating will make the seal. Visually one can see that as an optical ring that appears in the Press Tight, see fig 1. Problems may develop if the columns are not cut in an optimal way.
Fig.2 The most popular tool for column cutting: the "Ceramic Wafer"
There are several column cutting devices that you can use to cut the ends of fused silica capillary columns. One of the most used ones is called the “Ceramic Wafer’. This a square, flat tool, made out of a very hard material, see fig 2. Just by scratching the polyimide, the fused silica is reached and it takes just a little scratch to make the column break. If done correctly, a very good end-cut is obtained.
Fig. 3 gently slide the wafer along your nail
The general procedure for making a good end-cut is to make a fixed point on the fused silica using your nail, see fig. 3.
The ceramic wafer is gently moved along the nail in one direction leaving a little scratch. Then the end of the fused silica is slightly pressured with your finger and the column will break, see fig 4. If the end piece does not fall off, one can also bend it in the opposite direction and it will for sure fall off.
Fig.4 After scratching a little "tick" with your finger will make the column break
Now the critical part that all need to be aware off. The ceramic wafer has 2 different edges on the sides. It has a FLAT edge and a ROUGH edge on the sides. You can feel this when you move your nail over the sides of the wafer. Fig. 5 shows a magnification of such a wafer. It is very important, that for proper cutting of fused silica, one need to use the FLAT edge of the wafer.
Fig.5 Close up of Ceramic Wafer at 170x magnification. Note the FLAT and the ROUGH edge on the side. For cutting fused silica we need the FLAT side
If the ROUGH edge on the side is used, the polyimide gets damaged much more, see fig. 6. This will immediate lead to more difficulties with the column coupling, especially the PressTights connections.
Fig.6 Impact on fused silica polyimide coating using the FLAT and the ROUGH edges on the side of the wafer. The polyimide is damaged much more which will challenge making a good connection
This type of cutting is also important when fused silica columns are installed in a “uniliner” or an “on-column PTV liner”. Here we also prefer an optimal connection.