Question

(a) what are the relative advantages and disadvantages of packed and open tubular columns in gas chromatography?

(b) explain the difference between wall coated and porous-layer open tubular columns

(c) what is the advantage of bonding ( covalently attaching) the stationary phase to the column wall or cross-linking the stationary phase to itself?

Answer 1

a)advantages of packed columns:-

• A packed column is dense and evenly packed by solid support,
• They are particularly useful in the fixed gas and low molecular weight analyte area.
• Durability and cost
• They are capable of doing many 250ppm and above analyses for most applications.

disadvantages are

• small number of theoretical plates
• The packed particles have vapor gaps and do not conduct heat quickly to the core of the column.
• they require larger amount of gas to the detector

advantages of open tubular colums

• large number of theoretical plates
• They excell at low ppm to ppt analyte analyses.

disadvantages

• They are limited in phase selectivity options

b)wall coated open tubukar column(WCOT):-

The wall coated open tubular column consists of a capillary tube with its interior surface coated in a tiny layer of stationary phase. fused-silica is a common type, because it is stronger, inert, and flexible. Fused silica capillary tubes are made from purified silica that has a small quantity of metal oxides dispersed throughout the silica. The fused silica column also has a layer of polyimide on the outside of the column, which makes the column flexible and extends the life of the column. Wall-coated open tubular columns can also be made out of plastic, glass, stainless steel, aluminum.

porous layer open tubular columns:-

A porous-layer open tubular (PLOT) column is very similar to a support-coated open tubular column. The only difference between the two types of columns is that a PLOT does not have a liquid stationary phase. PLOT columns are used for gas solid chromatography. PLOT columns have a solid layer of carbon, molecular sieves, cyclodextrins, inorganic oxides, or porous polymers, coating the inner wall of the column.

c)it enhances the stationary phase stability and hepls in wide range of applications of WCOT colums in wide range of fields.