Capillary Chromatography - Back Flushing Techniques 2

After the solutes of interest have been eluted, the valve is rotated, and the connection of the column inlet to the sampling system is now directed to waste. At the same time the column exit is disconnected from the detector and connected to a separate carrier gas supply that forces a backward flow of carrier gas through the column and the strongly retained solutes are eluted to waste. As suggested above, to accelerate the purging process, the column temperature can be raised. When back flushing is complete, the valve is returned to the sampling position and the column temperature brought back to the initial conditions for analysis.

The sampling stage of the back flushing technique shown in figure 20 and depicts the sample passing through the valve to the column and from the column back to the valve and through the detector. The normal split injection system places the sample on the column.

 

Figure 21. Removal of Highly Retained Solutes in the Back Flushing Procedure

After the solutes of interest have been eluted, the valve is rotated, and the connection of the column inlet to the sampling system is now directed to waste. At the same time the column exit is disconnected from the detector and connected to a separate carrier gas supply that forces a backward flow of carrier gas through the column and the strongly retained solutes are eluted to waste. As suggested above, to accelerate the purging process, the column temperature can be raised. When back flushing is complete, the valve is returned to the sampling position and the column temperature brought back to the initial conditions for analysis.

 

Back flushing techniques are ideal for handling substances having a wide molecular weight or polarity range and can reduce analysis times or alternative simplify sample preparation.