Restek GC Column Selection Guide

Section V: Length

Longer columns provide more resolving power, increase analysis times, and cost more. Often an analyst must determine whether the amount of resolution increase is worth the extra time and expense. The benefits of using longer columns differ depending on whether isothermal or temperature programmed analyses are being performed.

For an isothermal analysis, retention time is dependent on length of the column. If the column length is doubled, the analysis time will double as well. However, the increase in resolution is only approximately 40%, since resolution is calculated using the square root of the length.

In the case of temperature programmed analyses, retention times are more dependent on temperature than column length. The increase in resolution is the same as an isothermal run, but there is only a marginal increase in analysis time.

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