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The retention gap technique in combination with on-column injection allows concentration of a large sample volume in the capillary column.
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choice of the retention gap depends on the solvent used:
the flooded zone after injection should be between 20 – 30 cm/µl
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Me-Sil retention gap
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only for use with n-hexane and diethyl ether
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Phe-Sil retention gap
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for all solvents except methanol and water
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CW retention gap
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for all solvents and especially for methanol and water
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calculation example: length of flooded zone ~ 20 – 30 cm/µl, retention gap 10 m x 0.32 mm ID,
capillary column: 25 m x 0.32 mm ID, max. injection volume ~ 30 – 50 μl
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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
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max. temperatures: for CW retention gaps 250 °C, for Me-Sil and Phe-Sil retention gaps 320 °C
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Retention gaps can also be used as transfer lines or precolumns (contamination capacity about 5 – 10 µg).
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