Reversed-phase high-performance liquid chromatography (RP-HPLC)
involves the separation of molecules on the basis of hydrophobicity. The separation
depends on the hydrophobic binding of the solute molecule from the
mobile phase to the immobilized hydrophobic ligands attached to the stationary
phase, i.e., the sorbent. A schematic diagram showing the binding of a peptide
or a protein to a reversed-phase surface is shown in Fig. 1. The solute
mixture is initially applied to the sorbent in the presence of aqueous buffers, and
the solutes are eluted by the addition of organic solvent to the mobile phase.
Elution can proceed either by isocratic conditions where the concentration of
organic solvent is constant, or by gradient elution whereby the amount of organic
solvent is increased over a period of time. The solutes are, therefore, eluted in
order of increasing molecular hydrophobicity. RP-HPLC is a very powerful
technique for the analysis of peptides and proteins because of a number of factors
that include: (1) the excellent resolution that can be achieved under a wide
range of chromatographic conditions for very closely related molecules as well
as structurally quite distinct molecules; (2) the experimental ease with which
chromatographic selectivity can be manipulated through changes in mobile
phase characteristics; (3) the generally high recoveries and, hence, high productivity;
and (4) the excellent reproducibility of repetitive separations carried
out over a long period of time, which is caused partly by the stability of the sorbent
materials under a wide range of mobile phase conditions (1,2). However,
RP-HPLC can cause the irreversible denaturation of protein samples thereby
reducing the potential recovery of material in a biologically active form.