PIEZOELECTRIC MECHANICAL PUMP WITH NANOLITER PER MINUTE PULSE-FREE FLOW DELIVERY FOR PRESSURE PUMPING IN MICRO-CHANNELS

A novel computer-controlled mechanical syringe pump is described which uses a piezoelectric actuator and a pivoted lever for amplification o f the linear displacement of the piezo-actuator to deliver solvents fr ee from pump pulsations at volumetric flow rates approaching 1 nl min( -1) even at high loading levels (high output pressures). The flow patt erns can be programmed by controlling-the voltage waveform to the piez o-actuator to produce a linear displacement of 72 mu m. By using the p ivoted lever, a ninefold amplification of the piezo-expansion was achi eved producing a total linear displacement of 648 mu m. When a gas-tig ht glass syringe of 1.0 mm diameter was interfaced to the piezo-pump, the total volume delivered in a single pump stroke was 511 nl. Whereas the pumping profile was governed by the expansion behavior of the pie zoelectric actuator, the flow rate was also slightly affected by the l oading pressure on the pump as well. The piezo-pump was found to deliv er adequately a stable flow of solutions with loading pressures as hig h as 3.79 x 10(5) Pa (actual loading pressure at the piezo-actuator = 3.41 x 10(6) Pa). Monitoring the flow stability using fluorescence ind icated that the volume flow was fairly noise free at pumping rates fro m 4 to 150 nl min(-1). Below a volume flow rate of 4 nl min-l, the pum p exhibited extensive noise characteristics due to the step resolution of the DAC driving the piezo-actuator, A diffuser-nozzle system was f abricated which allowed automatic refilling of the syringe pump and wa s micromachined into Plexiglas (PMMA) using X-ray lithography. The dif fuser-nozzle system contained channels that mere 50 pm in depth and ta pered from 300 to 30 mu m. The diffuser-nozzle system was interfaced t o the syringe pump by connecting conventional capillary tubes to the P MMA-based diffuser-nozzle, the piezo-pump and the chemical analysis sy stem.