GC062 Stationary Phases

 Stationary phases are usually liquids or very viscous polymers. The liquid phase must show high selectivity, α, for the compounds of interest. The capability of operating at high temperatures with minimal column bleed is also very important, particularly for sensitive detectors like FID, ECD and MS, used for trace analysis.

The most important types of liquid phases as of 2018 are the siloxane polymers (mixtures of methyl, phenyl, and cyano) polysiloxanes like the following:

·         OV‐1, SE‐30

·         DB‐1 (100% methyl polysiloxane)

·         OV‐17

·         OV‐275

·         DB‐1701

·         DB‐710

Another popular type is the polyelthylene glycol (Carbowax 20M, Superox®, and DB‐WAX®) liquid phases.

Contrary to packed columns, in capillary columns, the stationary phases are extensively cross-linked. Heating the freshly prepared capillary column at high temperatures and without gas flow in the column, the methyl groups form free radicals that readily cross-link, producing a more stable and higher-molecular-weight gum phase. Chemica bonding between fused silica surface and silanol groups is also feasible. These cross-linked and chemically bonded phases are more stable, last longer and can be cleaned by rinsing with solvents with cold. Most commercial capillary columns are of this type.

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