Cooperative effect in ion pairing of oligolysine with heptafluorobutyric acid in reversed-phase chromatography

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• 作者：Wenchun Xie ; Xu Qin ; Iwao Teraoka  ; ;   ; ^{teraoka@poly.edu} ; Richard A. Gross  ; ;   ; ^{rgross@poly.edu}
• 关键词：LC&ndash ; MS ; Single ion record (SIR) ; Ion-pairing chromatography ; Heptafluorobutyric acid (HFBA) ; Oligolysine
• 刊名：Journal of Chromatography A
• 出版年：2011
• 出版时间：28 October 2011
• 年：2011
• 卷：1218
• 期：43
• 页码：7765-7770
• 全文大小：607 K

文摘

The retention behavior of an oligolysine mixture, consisting of two to eight residues, was examined at different concentrations of heptafluorobutyric acid (HFBA) in the mobile phase using a C18 column. A single ion record (SIR) mode of the mass spectrometer produced a distinct retention time for each oligomer component. As the concentration of HFBA increased, the retention time of each oligomer increased. Furthermore, the increase in retention time is chain-length dependent such that, the longer the oligomer chain, the more rapid was the rate that retention time increased. A closed pairing model that presumes an equilibrium between the unpaired state and the paired state with a fixed number of HFBA molecules was used to analyze the retention factor as a function of [HFBA]. Curve fitting gave estimates of the ion-pairing equilibrium constant (K_ip,m), the distribution constant of paired oligolysine (K_D,ip), and the number of paired HFBA for each oligolysine (n). The plot of the fraction of paired oligolysine in the mobile phase, estimated from K_ip,m and n as a function of [HFBA], revealed a cooperative effect. In contrast, an open pairing model that assumes independent pairing of HFBA with each residue failed to describe the observed retention behavior.