Air Displacement Pipetting

TTP Ventus has developed a concept for an air displacement pipetting module enabled by our high-performance piezoelectric micropump, Disc Pump. This concept can enable devices that are smaller, lighter and lower cost than conventional air displacement systems.

This application page describes a simple system architecture that enables the pump to be used in an air displacement regime, exploiting the high-precision pressure control and pulsation-free output of the pump to deliver exceptional performance. This scheme also enables aspiration and dispensing without the need for additional valving to reverse the flow.

Contact TTP Ventus to speak to one of our experts about implementing this scheme in your next product.

Download Application Note pdf452.52 kB

Above: the system architecture includes the pump, an orifice (flow restrictor), a pressure sensor (Pr) and a reservoir volume (Vr), connected to a pipette tip.

Above: repeatability data for aspirated volume for three reservoir volume sizes, demonstrating CV of ~1% or better over much of the measurement range.

How it works

Step 1: With the tip above the fluid, the pump is turned on. The flow restriction created by the orifice causes the pressure in Vr to rise. The pump drive power is controlled so that a target pressure of P1 is reached in Vr. This elevated pressure provides an excess of stored air to ensure full and complete dispensing in step 5.

Step 2: The pipette tip is lowered into the fluid.

Step 3: The pump drive power is increased so that a higher target pressure, P2, is reached in Vr. An additional discrete quantity of air, proportionate to (P2-P1), is displaced from the tip into the system. The air pressure in the tip reduces, drawing fluid into the tip. The exceptional pressure regulation offered by Disc Pump in turn provides high-precision control over the quantity of fluid aspirated, Va.

Step 4: The pipette tip is withdrawn from the fluid.

Step 5: The pump power is reduced. The pressure in Vr discharges through the orifice into the tip. This results in fluid dispense from the tip. Dispense speed is controlled by the rate that the pump power (and therefore the pressure in Vr) is reduced - turning the pump off completely will result in the fastest dispense speed.