We explored the isocratic separation of an oligolysine mixture, consisting of two to eight residues (dp = 2 to 8) using different concentrations of heptafluorobutyric acid (HFBA) in ion-pairing chromatography. An expression derived from a closed pairing model which separated the ion-pairing equilibrium and partitioning of paired oligolysine from mobile phase to stationary phase was used to do the curve fitting on the plots of the logarithm of retention factor (k) of the oligolysine as a function of [HFBA] yielding three parameters including the ion-pairing equilibrium constant (Kip,m), the distribution constant of paired oligolysine (KD,ip), and the number of paired HFBA for each oligolysine (n). The relationship between n and dp and KD,ip and dp were investigated respectively. The plot of fraction of paired oligolysine as a function of [HFBA] revealed a cooperative effect in the formation of ion pairs in the mobile phase.

Cooperative effect observed in separation of oligolysine in ion-pairing chromatography using heptafluorobutyric acid

244th National Meeting (2012)

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