Gas Chromatography - Injection Devices > Retention Gap Sampling > Page 17

Retention Gap Sampling

The first solution to the problem of sample splitting was the 'retention gap method' which is depicted in figure 10.

Figure 10. The Retention Gap Method of Sampling

In this procedure stationary phase is removed from the first few centimeters of column. The sample is injected into this section and, if the sample becomes split, on commencing development, each split portion will still vaporize in the normal way. However, as there is no stationary phase present, the solutes will all travel at the velocity of the mobile phase until they reach the beginning of the coated section of the column. On reaching the start of the coating, the sample will be absorbed into the stationary phase and be concentrated at that point. As a result the sample is again at one point in the column. The retention gap procedure is normally used in conjunction with temperature programming, the program being initiated at a fairly low temperature. The lower temperature aids in the accumulation of all the solutes where the stationary phase coating begins. In order for this method of sampling to be successful there must be a significant difference between the boiling points of the sample solvent and those of the components of the sample.