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

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

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Gas Chromatography
Column bleeding occurs when

elution of the analyte is extended over time
the column is cracked and stationary phase leaks out
traces of the stationary phase are eluted
the column breaks during installation and causes personal injury

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