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Section 5 of 6 · Open sections

Required section · Section 5 of 6

Choose a technique, then read the pattern

You are setting up four transfers on the same bench: aqueous saline at room temperature, a volatile organic solvent, a viscous glycerol-based reagent, and a foaming protein-containing solution. For each liquid, decide whether standard forward pipetting with an air-displacement pipette is reasonable, or whether reverse pipetting or a positive-displacement pipette is the better-supported choice, using the liquid-behavior guidance from the focused-instruction section and your laboratory's SOP as the deciding authority.

Next, you are handed two replicate sets from two other pipettes on the same bench, both tested at a 100.0 uL setting. Set A shows five replicates tightly clustered between 98.6 and 98.7 uL, all consistently below nominal. Set B shows five replicates ranging from 99.3 to 100.7 uL, scattered on both sides of nominal. Decide what each pattern most directly suggests before reading the feedback.

Finally, apply the supplied local training criteria, absolute mean bias no greater than 1.0 uL and CV no greater than 0.50 percent at 100.0 uL, to decide whether Set A and Set B pass or fail. This decision uses only the criteria supplied for this exercise, because no universal pass or fail threshold exists across pipettes, tips, and laboratories.

A pass or fail decision is only as good as the criteria behind it; state which criteria you used, not just the number you calculated.

Illustrative drawing — this picture was drawn rather than captured.

Diagram comparing two replicate error patterns: a tight cluster offset from nominal volume, which points to systematic error, and a wide cluster centered on nominal volume, which points to random error.
Figure 1Systematic error looks like a tight cluster off target; random error looks like a wide cluster centered on target.

Illustrative drawing — this picture was drawn rather than captured.

Diagram of correct aspiration and dispensing checkpoints beside two immersion-depth errors: too shallow, which draws air, and too deep, which wets the tip barrel. The appropriate immersion depth comes from the current pipette/manufacturer procedure for the liquid and container.
Figure 2Technique checkpoints show vertical aspiration and consistent procedure-directed immersion depth beside too-shallow and too-deep errors.
Two replicate sets from a 100.0 uL gravimetric check on two different pipettes.
SetReplicate range (uL)Pattern
Set A98.6 to 98.7Tight cluster, consistently below nominal
Set B99.3 to 100.7Wide scatter, centered near nominal

Knowledge checks

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Knowledge check 1

For a foaming, protein-containing solution that tends to trap bubbles on forward dispense, which actions are reasonable next steps? Select all that apply.

Choose at least 2 options.

Knowledge check 2

Set A's five replicates cluster tightly between 98.6 and 98.7 uL at a 100.0 uL setting. What does this pattern most directly suggest?

Choose one option.

Knowledge check 3

Using the supplied local training criteria for this exercise, absolute mean bias no greater than 1.0 uL and CV no greater than 0.50 percent at 100.0 uL, how should Set A (98.6 to 98.7 uL, mean bias roughly -1.35 uL) be classified?

Choose one option.

Section status

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