Why Capillary Columns are preferred over Packed Columns in Gas Chromatography

A column is a major component of a Gas Chromatograph in which separation of sample components takes place. Gas chromatographic columns are classified into two major categories, namely, packed columns and capillary columns. The types of columns have been discussed in thefree course on gas chromatography.

Capillary Column

A question that often comes up is which Column to be used for a particular analysis. Your choice should be based on the general considerations discussed below:

Sample size

Today detectors come with high sensitivities so there is no need for large sample injections. In such situations capillary columns should be the preferred choice. However, if detector sensitivity is low then packed columns can be considered as these have higher sample load capacities.

Cost

Packed columns are less expensive than capillary columns. However, in comparison to capillary columns these have lower resolution efficiencies and larger column bleed.

Resolution Power

Capillary columns provide much better resolution leading to the desired separation between closely spaced peaks

Time saving

The ability to resolve components easily using capillary columns helps to increase laboratory throughput thereby increasing the number of samples that can be analysed in the same time.

Sample Polarity

Packed columns are generally made of stainless steel or glass. Stainless steel columns are generally useful for separation of non polar compounds whereas glass columns are suitable for polar compound separations

Ruggedness

Metallic columns are rugged in nature and can tolerate all types of handling but care should be taken not to drop them as this can disturb the packing inside the column and affect separation power. On the other hand glass packed columns have zero flexibility and also require careful handling. Capillary columns are fragile in nature and require very careful handling particularly at time of installation and removal inside the column oven.

It can be summarized that capillary columns offer almost all the desirable features required by the gas chromatographer and for this reason have replaced packed columns in almost all present day applications. The wide bore 0.53 mm id capillary column is able to accommodate large sample capacities and provide higher sensitivity than packed chromatographic column. Such columns are useful for trace component analysis or purity screening using direct injections.