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Study Notes: Column Ovens

Column temperature is a variable that must be controlled to a few tenths of a degree for accurate and precise work. The columns are usually coiled and housed in a thermostatically controlled oven to maintain temperature control. A photograph of an oven inside a GC.

The optimum column temperature depends on the boiling point of the sample and degree of separation required. A temperature equal to or slightly above the average boiling point of the sample will elute in a reasonable time - 2 to 30 minutes.

If the sample has a broad boiling range (due to the range of compounds in the sample) then temperature programming is used. The most volatile (ie lowest boiling point) compounds elute from the column first, followed in order down to the least volatile (ie highest boiling point) compound. This is similar in concept to gradient elution in Reversed Phase-HPLC but in the case of GC the temperature is raised continuously or in discrete steps.

For example,

A chromatogram demonstrating how temperature elution is used to effect good resolution between multiple peaks.

Notice that the temperature changes from 40 to 190°C during this GC run.

In general, optimum resolution is achieved at minimal temperature but this leads to increased elution time and the final conditions selected will often be a trade off between optimum resolution and a reasonable time to complete the analysis.

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