30
August/September 2010
Application of dynamic temperature gradients and profiles for capillary LC through the application of a new thermoelectric array based column heater
by David Collins, Damian Connolly, Dermot Brabazon, Mirek Macka and Brett Paull*, Irish Separation Science Cluster, Dublin City University, Ireland. *Contact author:
brett.paull.dcu.ie
Having a defined and well regulated control of temperature during chromatographic separations is of critical importance for every separation method. Capillary columns exhibit rapid thermal equilibration and precise application and control of longitudinal temperature gradients along the capillary column could provide interesting insights into band broadening processes within the column itself. By using thermoelectric modules in a platform column heater, simultaneous heating and cooling is possible. By creating an array of such modules with distinct thermally isolated zones, the generation of both static and dynamic temperature gradients and profiles along the length of the column can be created. The advantages and applications of such a system are numerous; increased separation efficiency, peak selectivity, temperature based trap and release, intermediate cooling or heating, flow through reaction control and thermal polymerisation to name but a few applications.
Thermoelectric modules, in this case Peltier modules, are used extensively in the electronics industry, usually for cooling components that are prone to overheating. The processor inside your PC is one example of a component that probably has a Peltier element attached to it. The operational principles behind thermoelectric modules is beyond the scope of this article, but suffice to say that they operate as a heat pump, drawing heat from one side of the device and emitting it on the other.
Construction Work was undertaken to construct a thermoelectric array of ten modules, which would use a simple heat exchanger to dissipate heat during cooling operations. The heat exchanger flows air through a series of fins attached to the bottom surface
the surface of each module measures the temperature of that module, while the
Figure 1. Array of thermoelectric modules with capillary column attached, showing; A. Heat Exchanger, B. Peltier Array, C. Capillary Column, D. Control Board
of each thermoelectric module – during cooling operations, this side of the modules will be the hot side, and so by dissipating this heat it allows the upper surface to cool. Each module is wired so that both heating and cooling can take place simultaneously along the array. A thermistor mounted on
power output to each one may be varied individually through a basic control board. The capillary column is
attached to the array using commercially available thermal paste which ensures good thermal conductivity between the array and the column. Since the thermal paste is not an adhesive it also allows for the easy removal of the column. Figure 1 shows a typical arrangement of a capillary column
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