Pump based on thermal expansion of a liquid for delivery of a pulse-free flow particularly for capillary chromatography and other microvolume applications

A new liquid delivery system has been designed which, without splitting, affords a constant pulse-free flow in the nanoliter to microliter range. A water-filled stainless-steel tubular spiral (or a coiled fused silica capillary) is immersed into a water bath in which temperature increments can be computer-programmed with high precision. When exposed to a (linear) temperature gradient, the enclosed water expands. The discharged water acts as a uniformly moving plunger which propels the mobile phase. Calculated flow rates obtained from a simple equation agreed with experimental values. The pump was developed because commercial piston pumps for HPLC do not perform satisfactorily at the low volumetric flows used in capillary chromatography: periodic variations in pressure and flow rate cause zone deformation and false peaks in the chromatograms. The thermal expansion pump is not based on any mechanically movable parts and is, therefore, ideal in the sense that it does not give rise to such disturbances. The potential of the pump is demonstrated by ion-exchange and hydrophobic-interaction chromatography experiments of proteins on the easy-to-synthesize continuous beds with 15-mu m and 320-mu m inside diameters (no frits to support the beds are required). The flow rates were 10 nL/min and 5.8 mu L/min when using pressure chambers of 0.11 and 11 mL, respectively. For larger volumes of the elution buffer, a greater internal volume of the pressure chamber and agitation of the enclosed liquid are required in order to achieve a rapid change in temperature.