Moving the piston in a pipet tip or barrel like a hypodermic syringe, with a disposable piston, describes which pipetting method?

Moving the piston in a pipet tip or barrel like a hypodermic syringe, with a disposable piston, describes which pipetting method?

• A. Air Displacement
• B. Capillary Displacement
• C. Pistonless Pipetting
• D. Positive Displacement

Answer: (D)

Direct contact between the piston and the liquid defines positive displacement pipetting. In this method the piston sits inside the tip or barrel and moves to aspirate and dispense the liquid, so the volume is set by the piston's displacement and there’s no air cushion between piston and liquid. The disposable piston helps prevent cross-contamination and is especially useful for viscous, volatile, or contaminant-prone samples, because the liquid’s properties don’t alter a separating air gap. By contrast, air displacement relies on an air cushion to transmit pressure to the liquid, making accuracy more sensitive to viscosity, volatility, and temperature. Capillary displacement uses capillary forces, and pistonless pipetting has no piston at all. Therefore, this setup describes positive displacement.

Direct contact between the piston and the liquid defines positive displacement pipetting. In this method the piston sits inside the tip or barrel and moves to aspirate and dispense the liquid, so the volume is set by the piston's displacement and there’s no air cushion between piston and liquid. The disposable piston helps prevent cross-contamination and is especially useful for viscous, volatile, or contaminant-prone samples, because the liquid’s properties don’t alter a separating air gap. By contrast, air displacement relies on an air cushion to transmit pressure to the liquid, making accuracy more sensitive to viscosity, volatility, and temperature. Capillary displacement uses capillary forces, and pistonless pipetting has no piston at all. Therefore, this setup describes positive displacement.