# Efficient and Symmetric Temperature Control in Capillary Electrophoresis II: Thermal Performance When Cooling Capillaries Are Tied Around Analytical Capillaries

## TL;DR

This paper introduces a new cooling system for capillary electrophoresis that provides efficient and symmetric temperature control.

## Contribution

A novel cooling system using microtubes tied around analytical capillaries for centrosymmetric temperature control is presented.

## Key findings

- A pressure gradient of 0.25 bar/cm in the cooling liquid efficiently removes heat.
- The system allows for very high and stable electric currents under strong electric fields.
- The new system outperforms traditional cooling methods in terms of symmetry and efficiency.

## Abstract

Current commercially available capillary electrophoresis instruments lack centrosymmetric and efficient temperature control along the whole extend of the capillary. Here we studied the characteristics and thermal performance of a cooling system that consists of cooling capillaries (fused silica microtubes) which are tied around the complete extent of the analytical capillaries. Six cooling capillaries with only 75 µm inner diameter (320 µm outer diameter—without polyimide) were tied around the outer surface of 320 µm outer diameter analytical capillaries (also without polyimide). The tying process is detailed in a previous publication (J Sep Sci. 2025; 48: e70081. https://doi.org/10.1002/jssc.70081). The application of a pressure gradient of 0.25 bar/cm in the cooling liquid was enough to efficiently remove heat and control temperature. Very strong electric fields could be applied, producing very high and stable electric currents. Fields beyond 3500 Volts/cm were applied in a 50 µm inner diameter capillary filled with 20 mM sodium phosphate buffer solution at pH 7.20 and the coolant set at 25°C. This cooling system outperformed the two most used systems: forced air and recirculating liquid coolant in a tube with a capillary inside. The spatial steady‐state temperature profiles of the systems were simulated by numerically solving the heat equation using a finite element method. The centrosymmetric temperature profile and efficiency of this cooling system was corroborated by these numerical results. An objective parameter indicating cooling asymmetry was introduced and used to quantify the superior performance of this new cooling system.