Excess Adsorption of Organic Eluent Components from Mobile Phases Containing Electrolytes
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The excess adsorption isotherms of organic eluent components from solutions containing electrolytes on a C18-bonded stationary phase are investigated by frontal analysis in staircase mode. The excess adsorption of acetonitrile increases when NaHSO4, NaH2PO4, NaCl, or NaOAc is added to the eluent, but decreases upon addition of NaBr or NaClO4. The excess adsorption of acetonitrile increases in the order of NaCl, NaHSO4, NaH2PO4 > NaOAc > NaBr, NaClO4. On the other hand, the effect of electrolyte addition on the excess adsorption of methanol is not significant. The effect of electrolytes on the retention of alkylbenzenes in reversed-phase liquid chromatography is discussed on the basis of the excess adsorption of organic eluent components. The retention of alkylbenzenes shows negative correlation with the excess adsorption of acetonitrile. This indicates that the acetonitrile layer on the stationary phase does not act as a part of the stationary phase. A developed acetonitrile layer reduces the retention of alkylbenzenes by the competitive adsorption at the interface between the organic layer and the stationary phase.
KeywordsReversed-phase liquid chromatography Excess adsorption Retention mechanism Electrolyte
The authors are grateful to Ms. T. Oata, Ms. A. Eto, Ms. S. Oguma and Dr. N. Suzuki (Daiichi Sankyo, Japan) for their continuous encouragement.
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Conflict of interest
The authors declare no conflict of interest in relation to this research.
This article does not contain any studies with human participants or animals performed by any of the authors.