Classification of Chromatographic Methods

Classification of Chromatographic Methods (Geometry)

• Planar– Paper– Thin layer

• Column– GC– HPLC– IC– SFC

Classification of Chromatographic Methods (Mobile Phase)

• Gas Chromatography• Liquid Chromatography• Supercritical Fluid Chromatography

Classification of Chromatographic Methods (Stationary Phase)

• Adsorption• Partition• Ion-Exchange• Molecular Exclusion• Affinity

Example of Affinity Chromatography

Purification of monoclonal antibody on a 5 cm x 4.6 mm column with protein A covalently attached to a polymer support

A Hot Idea: Molecular Imprinting

An “artificial antibody” can be constructed by synthesizing a polymer in the presence of a template molecule. When the template is removed, the polymer is “imprinted” with the shape of the template and with complementary functional groups that can bind to the template. The imprinted polymer can be used as a stationary phase in affinity chromatography.

Molecular Imprinting

Hydrophobic Interaction Chromatography (HIC)

• Based on the interaction of a hydrophobic stationary phase with a hydrophobic region of a solute such as a protein

• A protein can have hydrophilic regions that make it soluble in water and hydrophobic regions interacting with a hydrophobic stationary phase

• Proteins are adsorbed on the hydrophobic surface when the aqueous mobile phase contains high salt concentration

• Eluent strength is increased by decreasing the salt concentration

Hydrophilic Interaction Chromatography (HILIC)

• Most useful for small molecules too polar to be retained by reversed-phase HPLC

• Stationary phases are strongly polar• The mobile phase contains ≥ 80% polar

organic solvent mixed with water

Hydrophilic Interaction Chromatography (cont.)

• Solute equilibrates between the mobile phase and a layer of aqueous phase on the surface of the stationary phase

• Eluent strength is increased by increasingthe fraction of water in the mobile phase. (In NP HPLC, the solvent is nonaqueous. In RP HPLC, eluent strength is increased by decreasing the fraction of water in the mobile phase).

Modes of Chromatographic Separation:

• Frontal analysis• Displacement development• Elution development

Frontal Analysis

• The liquid or gas mixture is fed into a column containing a solid packing

• The mixture acts as its own mobile phase• The separation depends on the ability of each

component to be sorbed• Once the packing is saturated, the mixture flows

through with its original composition• The least-sorbed component breaks through first

and is the only component obtained in a pure form

Displacement Development

• The developer is contained in the mobile phase

• The mobile phase must be more sorbed than any sample component

• A single pure band of the first component is obtained

• There is always an overlap zone for each succeeding component

Elution Development

• Sample components travel through the column at rates determined by their retention on the solid packing

• A complete separation is possible

Isotherms

An isotherm is a graphical representation of the interaction of an adsorbent and a solute in solution (gas or liquid) at a specified temperature. The isotherm is a graphical representation of the partition coefficient or distribution constant K:

G

S

CC

K =

G

S

CC

K =

Process Types in Chromatography

• The process of chromatographic separation is defined by two conditions:– The distribution isotherms may be linear or

nonlinear– The chromatographic system is either ideal or

nonideal.

Ideal Chromatography

• The exchange between the two phases is thermodynamically reversible

• The equilibrium between the two phases is immediate (longitudinal diffusion can be ignored and the mass transfer is very high)

• In nonideal chromatography, these assumptions cannot be made

Partition chromatography

Liquid-solid chromatography

Gas-solid chromatography