When loading an autopipette with liquid, to which stop do you depress the plunger?

Question

BlackTom AI · Accepted Answer

The correct answer is "First stop only" because the first stop on a micropipette sets the piston position that draws up the precise set volume; the second stop is a blow-out used only to expel residual liquid when dispensing.

1) Relevant knowledge points and concepts
- Micropipettes have two tactile stops on the plunger: the first stop (volume stop) and the second stop (blow-out).  
- Depressing to the first stop displaces the exact volume of air needed to aspirate the set liquid volume when released.  
- Depressing to the second stop expels extra air beyond the set volume to force out residual liquid (used when dispensing, not aspirating).

2) Step-by-step reasoning process
- To load (aspirate) liquid, you depress the plunger to the first stop and hold it there.  
- Immerse the tip just below the liquid surface (a few millimeters).  
- Slowly release the plunger to the resting position; the returned air volume draws the set volume of liquid into the tip.  
- Withdraw the tip from the liquid and proceed to dispense.

3) (No numerical calculations are required here; procedural steps above show the operational sequence.)

4) Why the correct answer is correct
- The first stop corresponds exactly to the calibrated displacement needed to aspirate the set volume. Using the first stop ensures accurate and reproducible uptake. Depressing further (to the second stop) before aspiration changes the displaced air volume and will either under- or over-fill the tip when released, reducing accuracy and risking aerosol formation.

5) Why the other options are incorrect
- "Straight to second stop": depresses beyond the calibrated volume and will cause incorrect aspiration when released.  
- "First stop, pause, then second stop": that sequence is for dispensing to ensure complete expulsion (first stop to dispense, second stop for blow-out). It is not the correct action for loading liquid.

6) Conclusion
Following proper pipetting technique, you depress the plunger to the first stop only when loading an autopipette. This confirms the provided answer: "First stop only."

When loading an autopipette with liquid, to which stop do you depress the plunger?单项选择题

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