Question

Explain the advantages and disadvantages of open tubular vs packed columns. Why aren’t packed columns use with HPLC?

Answer 1

A) Advantages and Disadvantages of open tubular and packed column

1) Open tubular column ( Capillary columns)

It is capillary tubing of internal diameter of about 0.3-0.5 mm. Inner wall of column are coated with a very thin film of liquid which acts as stationary phase.

Advantages:

a) The capillary column offers negligible resistance to the flow of mobile phase and hence pressure inside the column is less. therefore the column as long as 10-100 m can be used.

b) Due to longer length, these column consists of greater number of theoretical plates and hence efficiency of separation is higher.

c) Require only small amout of sample

d) Higher resolution

Disadvantages:

a) Since these columns contain limited amount of stationary phase, they suffer from very low sample loading capacity.

2) Packed column

These column contain fully packed stationary phase made of fine particles.

Advantages:

a) Higher sample loading capacity

Disadvantage:

a) Require large amount of sample

b) short column length and hence less number of theoretical plates therefore lower efficiency of separation.

c) poor resolution

B) In case of HPLC, packed columns are used because packed columns have larger surface area for interactions between analytes and the stationary phase, and thus they may have have higher sample capacity than capillary columns. Capillary columns are used in GC.