Question

Please answer
Explain the factors that contribute to band broadening in chromatographic separations, and how band broadening can be minimized?

Answer 1

Factors that contribute to the band broadening in chromatographic separations.

1) A = Eddy Diffusion(Multi Path Effect)

2) B = Random Molecular Diffusion

3) C = Mass Transfer within particle caused by Mobile phase

Eddy Diffusion

It explains about the alteration in mobile phase flow or analyte flow path among the chromatographic column. A molecule of an analyte will choose more path through the column which form because of small differences in the particle size of the packing material and inhomogeneities in column packing. The analytes band gets broader due to this multiple path when it navigates through the column.

Longitudinal Diffusion

In an injection solvent, the band of analyte molecules are present and due to the concentration gradient they scattered in all direction at the outer edges of the band. The extent of broadening is along the axis of flow. Band broadening will takes place, simultaneously the column will experience some ill effects.

Mass Transfer

According to Mass Transfer the mobile phase is stationary, but the stationary phase matter is porous. For the Separation to takes place the packing material is porous to give way for large surface area.

Band Broadening can be minimised by minimising these effects

Eddy diffusion can be minimised by

a) Employing particles with narrow size distribution.

b) Applying smaller stationary phase particles

c) Choosing well packed columns

Longitudinal Diffusion can be minimised by

a) Usage of perfect nuts, ferrules and fittings likely everwhere

b) By employing higher mobile phase flow rates

c) Maintaining the system tubing narrow and short, cautious with back pressure.

Mass Transfer can be minimised by

a) By Heating the column.

b) With Smaller diameter stationary phase particles

c) Applying lower mobile phase flow rates.