Column Basics

Classification of packing materials in common chromatographic columns

a, reversed-phase (with ion pair) method

C18 (octadecyl or ODS) ------------- Good universality; strong retention, wide use

C8 (octyl) -------------Similar to C18, but with slightly less reserved value

C3, C4 ------------- small retention value; mostly used for peptides and proteins

C1 [trimethylsilane (TMS)]------ the smallest retention value; the most unstable

Phenyl, phenethyl ------------- moderate retention; selectivity varies

CN (cyano) ------------- Moderate retention; both normal phase and reverse phase can be used

NH2 (amino) ------------- weak retention; used for hydrocarbons; less stable

Polystyrene-based b ------------- Stable in the mobile phase of 1 < PH < 13; good peak shape for some separations, long column life

b. Normal phase method

CN (cyano group) ------------- Good universality; moderate polarity; wide use

OH (diol group) ------------- more polar than CN

NH2 (Amino) ------------- High polarity, less stable

Silica gel b------------Good universality; cheap; inconvenient to operate; used to prepare LC

c, steric exclusion method

Silica gel b ------------- Excellent universality; used as adsorbent

Silanized silica gel ------------- Weak adsorption, good solvent compatibility; suitable for organic solvents

OH (diol group) ------------ less stable; used in aqueous SEC (gel filtration)

Polystyrene b ------------ Widely used in organic SEC (gel permeation); generally incompatible with water and polar organic solvents

d, ion exchange method

Bonded phase ------------ Stability and reproducibility are not good

Polystyrene-based b ------------- not high column efficiency; stable; good reproducibility