Sub-ambient temperature effects on the separation of monosaccharides by high-performance anion-exchange chromatography with pulse amperometric detection. Application to marine chemistry.

The effects of column temperature in the range 10-45 degrees C using high-performance anion-exchange chromatography (HPAEC) and pulse amperometric detection are described for the determination of monosaccharides. The influence of temperature was tested with an isocratic elution of NaOH at concentrations varying from 2.5 to 20 mM and with a post-column addition of 1 M NaOH. The results showed that small changes of temperature greatly affect retention times and resolution (Rs) of monosaccharides and particularly those of the both pairs xylose-mannose and rhamnose-arabinose which cannot be simultaneously detected at usual room temperature (approximately 25 degrees C). Our results suggest that a subambient temperature of 17 degrees C and an eluent concentration of 19 mM are the more appropriate conditions for an acceptable separation (R(s rha/ara) = 1.02, R(s man/xyl) = 0.70) in a short analytical run time (35 min). The results showed that within the range of temperatures studied, enthalpy and entropy are invariant of temperature indicating that changes in the retention processes are mainly due to temperature than other associated changes in the system. This study demonstrated the importance of controlling temperature during HPAEC of monosaccharides, both to accomplish highly reproducible retention times and to achieve optimal separation of sugars. This method gave acceptable results for detection of marine sugars.