Positive Displacement Pipettors

Positive displacement pipettes are specifically designed to handle liquids that would otherwise compromise the accuracy of standard air-displacement instruments. Rather than using a compressed air cushion, positive displacement utilizes a piston that descends directly into the capillary tip to physically expel the contents, wiping the walls clean and leaving negligible residual volume behind. Liquids with specialized physical properties, such as viscous reagents, volatile solvents, foaming buffers, oils, resins, and concentrated protein solutions, can all be dispensed reliably using this principle. Many positive displacement pipettes also support repeat dispensing, allowing a single aspiration to be divided into multiple precisely defined aliquots without refilling, which is particularly valuable when working with limited quantities of difficult or high-cost reagents. When comparing instruments across manufacturers, the key specifications to evaluate include volume range, compatible capillary tip formats, per-tip consumable costs, and repeat dispensing capability.