COMBINATION OF COLUMN TEMPERATURE-GRADIENT AND MOBILE-PHASE FLOW GRADIENT IN MICROCOLUMN AND CAPILLARY COLUMN HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

The combination of several gradient modes (solvent, temperature, and f low programming) is rarely used in HPLC analysis, In this work, the se parations obtained utilizing simultaneous flow and temperature gradien t in capillary column and microcolumn HPLC were compared with the sepa rations performed under isocratic, isothermal, and isorheic (constant flow) conditions. When the mobile phase flow rate and the column tempe rature were changed simultaneously during the separation run, the anal ysis time was shortened up to 50%, while the separation efficiency was preserved. The separations obtained with combined temperature and flo w gradients show high reproducibility (relative standard deviation <2. 0%), comparable to the reproducibility normally seen with a mobile pha se gradient. For capillary HPLC, simultaneous temperature and flow pro gramming is the method of choice because of the great technical diffic ulties involved in performing solvent gradient elution.