Monitoring temperature changes in capillary electrophoresis with nanoliter-volume NMR thermometry

Nanoliter-volume proton nuclear magnetic resonance (NMR) spectroscopy is us ed to monitor the electrolyte temperature during capillary electrophoresis (CE). By measuring the shift in the proton resonance frequency of the water signal, the intracapillary temperature can be recorded noninvasively with subsecond temporal resolution and spatial resolution on the order of 1 mm. Thermal changes of more than 65 degrees C are observed under both equilibri um and nonequilibrium conditions for typical CE separation conditions. Seve ral capillary and buffer combinations are examined with external cooling by both liquid and air convection. Additionally, NMR thermometry allows noneq uilibrium temperatures in analyte bands to be monitored during a separation . As one example, a plug of 1 mM NaCl is injected into a capillary filled w ith 50 mM berate buffer. Upon reaching the NMR detector, the temperature in the NaCl band is more than 20 degrees C higher than the temperature in the surrounding buffer. Such observations have direct applicability to a varie ty of studies, including experiments which utilize sample stacking and isot achophoresis.