Gas Chromatography
A retention gap is placed between the injector and the front of the column to

retain contaminants and prevent them from reaching the column
All of these
retain the sample and release it gradually to the column
prevent backflush of the injected solution

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Gas Chromatography
In column switching chromatography

one column is removed and replaced by another
compounds trapped on one column are eluted to another column
any of the above
the flow to the column is switched on and off repeatedly

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Gas Chromatography
Split injection is carried out by

splitting the sample into smaller portions to inject at the same time through parallel ports
None of these
splitting off some of the sample so that it does not enter the column
splitting the sample into smaller portions to inject sequentially

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