Column Oven:
The column(s) are located in an oven that can be operated either at constant temperature (isothermal) or using a series of temperature holds and ramps (gradient elution or temperature programming). This allows the separation of individual sample components to be controlled and optimised. Columns come in two types: packed and capillary . Most gas chromatography today is performed using capillary columns, as they offer significant advantages for most samples.
The fan at the rear of the oven ensures temperature uniformity throughout the oven, as well as the ability to ramp the column temperature in a controlled and reproducible manner. This feature is particulary important when dealing with complex samples containing components having a wide range of boiling points, as run times would be prohibitively long otherwise. The temperature can typically be varied from slightly above ambient (about 35 °C) to above 300 °C; this upper limit is determined by the thermal stability of both sample components and the column stationary phase.
Capillary Columns:
Capillary (or open tubular) columns are typically between 15 and 60 metres long, with internal diameters of 0.10 to 0.53 mm. There are several variants, but generally the stationary phase is a 1 to 5 µm coating on the interior wall of the column. A combination of the narrow diameter and a lack of any obstructions to the flow path results in columns with extremely high resolving power yet reasonable run times.
The very small mobile and stationary phase volumes within the column require small sample volumes (typically less than 1 µL actually injected on to the column) and lower flow rates than would be the case for the equivalent packed column. These features provide the best compatibility with the operating requirements of a mass spectrometer. Advances in mass spectrometer and computer technology have led to the widespread adoption and commercial success of bench-top GC-MS systems.
Continue the tour:
GC-MS: Injectors/Detector → Columns → Mass Spec