GC Instrument Operation Column Temperature and Elution Values

6 GC INSTRUMENT OPERATION (COLUMN TEMPERATURE AND ELUTION VALUES) 

Finally, we reach the discussion of the most easily adjusted variable controlling GC peak elution. Recall from Chapter 11 that for a given stationary phase, the temperature of the column is the primary determinant of the equilibrium partition ratio between the stationary and mobile phases. 

Chromatogram using a FAST (10 m X 0.1 mm i.d.) BPx5 column with a 0.10 nm film. 

The larger the percentage of time the analjrte spends in the gas flow of the mobile phase, the more quickly it elutes from the column. A modern GC instrument is designed to very precisely and repro-ducibly control the temperature of the oven compartment in which the coiled-up column resides. This will promote reproducible retention times to enable peak identification. 

In a very simple GC analysis of a group of similar anal)rtes that would elute close together, the analyst chooses an appropriate stationary phase, optimizes its film thickness, and selects the necessary column diameter and length, all as outlined in Section 12.5. Then the oven is set to a column temperature where k for these analytes is between 2 and 10 (cf. Equation 11.3). The highest value of temperature T at which adequate resolution of the closest eluting pair is observed will yield the fastest analysis. Such 

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