On-line temperature monitoring in a capillary electrochromatography frit using microcoil NMR

A new nuclear magnetic resonance (NMR) spectroscopy probe has been designed to measure the temperature of the water inside a capillary. The probe provides the ability to measure the temperature in a several hundred micrometer long capillary section, corresponding to liquid volumes in the picoliter to nanoliter range with a temperature monitoring accuracy of 0.2 degrees C. The NMR probe is based on a novel two-turn vertical solenoidal design, and its performance for capillary-scale temperature measurements is characterized. The temperature rise in a chromatographic frit of the type used in capillary electrochromatography is measured as a function of applied power, and temperature rises of more than 50 degrees C are observed. The temperature of the electrolyte cools rapidly after exiting the frit and can be followed as a function of distance from the frit. The ability to accurately monitor the temperature of water as it moves through porous materials such as packed chromatographic beds and frits is important to allow the effects of temperature on CEC separation performance to be determined.