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 splittin g, affords a constant pulse-free flow in the nanoliter to microliter r ange. 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 expose d 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 ag reed with experimental values. The pump was developed because commerci al piston pumps for HPLC do not perform satisfactorily at the low volu metric flows used in capillary chromatography: periodic variations in pressure and flow rate cause zone deformation and false peaks in the c hromatograms. The thermal expansion pump is not based on any mechanica lly movable parts and is, therefore, ideal in the sense that it does n ot give rise to such disturbances. The potential of the pump is demons trated by ion-exchange and hydrophobic-interaction chromatography expe riments 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 r equired). The flow rates were 10 nL/min and 5.8 mu L/min when using pr essure 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.