Biochemical Techniques and Instrumentation

2.6.3.3.2. Capillary column

Capillary columns are made of metal, plastic, glass or fused silica. They have very small internal diameter of a few tenths of a millimeter. Capillary columns are in general more efficient than packed columns. They are two types of capillary columns:

1. Wall-coated open tubular (WCOT): WCOT columns consist of a capillary tube whose walls are coated with liquid stationary phase.
2. Support-coated open tubular (SCOT): SCOT columns has a capillary tube whose inner wall is lined with a thin layer of support material onto which liquid stationary phase is adsorbed. SCOT columns are generally less efficient than WCOT columns.

A more recent introduction is the Fused Silica Open Tubular (FSOT) column. They have much thinner walls than glass capillary columns. They have a polyimide coating that gives strength to the column. They are flexible and wound into coils. They have good physical strength, flexibility and low reactivity.

Film thickness of the stationary phase directly influences the retentive character and capacity of a column. The increase in film thickness leads to an increase in solute retention. The capacity of the column is directly related to film thickness, diameter and stationary phase polarity.