Temperature - the tool in separation of alkaloids by RP-HPLC

The retention behavior of 12 alkaloids on two different stationary phases, was based on silica matrix C-18 and pentalluorophenyl by use of aqueous eluents consisting of acetonitrile, water, acetate buffer, and ion-pair reagent (OSA-Na) or silanol blocker (DEA). The retention coefficients and values of asymmetry factor and theoretical plate number were measured in the temperature range 10-50 degrees C. Relationships between In k vs. I/T were created for alkaloids in all investigated chromatographic systems. In IP-RP systems typical van't Hoff plots - linear decrease of retention with the increase of temperature have been obtained. In the case of systems with DEA, relationships were untypical - the increase of retention with the increase of temperature in most cases. Temperature changes also caused changes in system efficiency and peak symmetry. In most cases, the increase of efficiency with the increase of temperature was observed to be the maximum, and than a slight decrease of theoretical plate number values were observed. Symmetry of peaks gets better with the increase of temperature in most cases.