Temperature effect on retention and separation of poly(ethylene glycol)s in reversed-phase liquid chromatography

The isocratic retention of poly(ethylene glycol)s (PEGs) is studied on an octadecyl (C18) bonded-phase column at different temperatures. Linear relationships between the natural logarithm of the capacity factor (In k') and the inverse of temperature (1/T) are found. Some thermodynamic parameters, such as the apparent change of enthalpy (ΔH°) and the apparent change of entropy (ΔS°), are obtained using van't Hoff plots. Principal component factor analysis (PCFA) and target transformation factor analysis (TTFA) are used to analyze the retention data. The PEG molar mass is found to be a real factor in the solute space, and unknown molar mass can be calculated via the "free-floating" method. The information obtained from the thermodynamic study is discussed in developing strategies for separation of homopolymers and copolymers according to the end-group functionality.