Which statement best describes the purpose of the first stop on a micropipette in a transfer?

Which statement best describes the purpose of the first stop on a micropipette in a transfer?

• A. First stop: draw up the correct volume; Second stop: expel liquid
• B. First stop: expel liquid; Second stop: draw up
• C. First stop: discard tip; Second: dispense
• D. First stop: calibrate; Second: mix

Answer: (A)

The key idea is how a micropipette uses two stops to control a precise transfer. The first stop is the stop you press to aspirate; when you draw up, the plunger moves to this point and pulls a specific, set volume of liquid into the tip. This is where the measurement is defined—the volume you’ve dialed in is drawn into the tip. The second stop is used to dispense. Pressing past the first stop to the second stop pushes that same volume out of the tip, ensuring you deliver the exact amount you drew up. This two-step action—first drawing in the correct volume, then driving it out—keeps the transfer accurate and helps avoid under- or over-delivering. So, describing the first stop as drawing up the correct volume and the second as expelling the liquid matches how the pipette is designed to function: you set the volume, aspirate to the first stop to capture that volume, then dispense by going to the second stop.

The key idea is how a micropipette uses two stops to control a precise transfer. The first stop is the stop you press to aspirate; when you draw up, the plunger moves to this point and pulls a specific, set volume of liquid into the tip. This is where the measurement is defined—the volume you’ve dialed in is drawn into the tip.

The second stop is used to dispense. Pressing past the first stop to the second stop pushes that same volume out of the tip, ensuring you deliver the exact amount you drew up. This two-step action—first drawing in the correct volume, then driving it out—keeps the transfer accurate and helps avoid under- or over-delivering.

So, describing the first stop as drawing up the correct volume and the second as expelling the liquid matches how the pipette is designed to function: you set the volume, aspirate to the first stop to capture that volume, then dispense by going to the second stop.