The retention gap technique in combination with on-column injection allows concentration of a large sample volume in the capillary column.
Choice of the retention gap depends on the solvent used: the flooded zone after injection should be between 20–30 cm/µL
- Me-Sil retention gap only for use with n-hexane and diethyl ether
- Phe-Sil retention gap for all solvents except methanol and water
- CW retention gap for all solvents and especially for methanol and water
A retention gap must be inert without any noticeable retention.
Me-Sil retention gaps are more inert than Phe-Sil, while Phe-Sil is less susceptible to contamination.
Max. temperatures:
- CW retention gaps 250 °C
- Me-Sil and Phe-Sil retention gaps 320 °C
Retention gaps can also be used as transfer lines or precolumns (contamination capacity about 5–10 µg).