Temperature difference between the cooled and the noncooled parts of an electrolyte in capillary electrophoresis

Joule heating always accompanies electrophoresis and unavoidably leads to a temperature increase of the electrolyte. The elevated temperatures are known to adversely affect the quality of separation and detection. To minimize the temperature increase in capillary electrophoresis (CE), Joule heat is removed by actively cooling the capillary. However, there are always small parts of the capillary, such as its inlet, outlet, and detection window, which are not actively cooled. The noncooled capillary inlet has been recently proven to have an elevated temperature which is high enough to significantly affect CE-based quantitative affinity analyses. The temperature difference between the cooled and noncooled regions has never been determined due to the lack of a suitable method. Here, we report on the first experimental determination of temperature in the cooled part of the capillary and the noncooled inlet region of the capillary. We found that, under typical CE conditions, with a low-conductivity run buffer, the temperature in the noncooled inlet exceeded the temperature in the cooled region by more than 15 °C. High-conductivity buffers are anticipated to have even greater temperature differences between the noncooled and cooled capillary parts. Our results strongly suggest the potential effect of the noncooled capillary regions on the quality of CE-based analyses, which cannot be ignored. The simplest way to avoid potential errors is to move the sample to the cooled region by pressure or by applying a low electric field.