Efficient and Symmetric Temperature Control in Capillary Electrophoresis I: Tying Cooling Capillaries Around Analytical Capillaries

The heat generated by the Joule effect during capillary electrophoresis (CE) runs creates radial temperature gradients in the separation medium. These temperature gradients cause zone dispersion in addition to molecular diffusion. This severely limits the field strengths that can be applied during the runs, especially when solutions with high ionic conductivity are used. This greatly increases run times, especially when high separation efficiencies are sought. In this work, the author proposes tying cooling capillaries (fused silica microtubes) along the external surface of the analytical capillary, allowing the circulation of coolants to efficiently and symmetrically control temperature in CE. The author deduced, step-by-step, the three master equations that serve as guidelines to produce a good match and tightly secure cooling capillaries along the outer surface of analytical capillaries. Additionally, an automated capillary tying machine was developed and demonstrated. Sets were produced with: four, five, and six cooling capillaries tied around one analytical capillary. The outer diameters of the capillaries used (one analytical and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:semantics><mml:mi>n</mml:mi> <mml:annotation>$n$</mml:annotation></mml:semantics> </mml:math> cooling) and the values of the remaining voids left between the first and last cooling capillary are in good agreement with the predictions of the three master equations deduced in this work. To the author's knowledge, this is the first time that cooling capillaries were tied around analytical capillaries to produce an efficient and symmetric cooling system for CE and toroidal capillary electrophoresis.