Capillary Column: Types and its Importance
Capillary Columns are columns formed by Chromatography. It is the technique of separating the different components of a sample based on their various physical and chemical properties. There are two types of phases involved in chromatography. One is the mobile phase, which along with the sample moves over the stationary phase. Various constituents of the sample move with different speeds over stationary causing them to separate. The core principle of separation is the differential partitioning of sample constituents between the mobile and stationary phases.
There are different types of chromatography techniques, each having a different mechanism of separation. One such type is column chromatography in which the stationary phase is within a tube or a column. Gas chromatography is a kind of column chromatography in which volatile samples can be separated in its components. In gas chromatography, gas is the mobile phase, whereas column coating in the inner surface acts as a stationary phase. The vapourised sample is separated on the basis of how long the components of the sample take to come out from the other end of the column and pass into the detector.
The time components take to come out from the column is called the retention time. Different types of columns, coated with different types of stationary phases are available in the market. The type of stationary phase being used depends on the type of compounds you want to separate or analyze.
GC CAPILLARY COLUMN
GC Capillary columns are the columns of gas chromatography, they have a coating of stationary phase on the inner surface of the column rather than being packed with the stationary phase. Capillary GC columns are used in analytical chromatography, to determine the presence and concentration of the individual chemical compounds that the sample contains.
The GC capillary column is widely used in petroleum industries and pharmaceutical industries to test the presence of impurities (unwanted constituents) in the sample or drug and in the medical field it is used to determine the constituents of the sample. As compared to the packed column, a GC capillary column provides more resolved and faster separation.
One limitation of the GC capillary column is that it gets overloaded easily on adding too much of the sample. There are various types of capillary GC columns available in the market based on differences in their size, length polarity, whether or not the column has the cap in its end.
Because the stationary phase is coated on the inner surface of the column, hence the film thickness in the description determines how thick is the coating inside the column. GC Capillary columns come in different dimensions from 12 to 60 m in length and with different internal coating thicknesses, diameters and stationary phases so they can be modified according to the type you want to separate.
In the capillary GC column, the mobile phase along with the sample moves across the column due to the pressure difference between the inlet where the gas is pumped in and the outlet end from where analyte comes out of the column and gas is leaving. The analytes move with different speeds over the stationary phase due to their interactions with the stationary phase particles. How long they take to come out of column determines how quickly they travel through the column and become the basis of their separate inside the column.
