This technical note from Phenomenex discusses the use of mobile phase pH to control analyte ionization states (pH-LC) in RP-HPLC as a highly effective way to change selectivity. The ionized species of an analyte is shown to have higher polarity (less hydrophobicity) than the neutral species, which results in a loss of expected retention for that analyte. With the use of mobile phase pH in conjunction with a pH-stable column, powerful selectivity manipulation can be achieved.
