Micropipette Basics and Techniques

Micropipettes are essential tools in the molecular biology lab for accurately measuring very small volumes.
They enable a wide range of experiments and are generally similar across brands (with model-specific differences).
Four main sizes are commonly used: $1000\,\mu\text{L},\; 200\,\mu\text{L},\; 20\,\mu\text{L},\; 10\,\mu\text{L}$ .
A microliter is a very small unit: $1\,\mu\text{L} = 10^{-6}\,\text{L}$ (one millionth of a liter).
Proper technique and calibration ensure accuracy and reduce the risk of contamination.

Four main sizes: $1000\,\mu\text{L},\; 200\,\mu\text{L},\; 20\,\mu\text{L},\; 10\,\mu\text{L}.$
Volume ranges are specific to each pipette; you must use a pipette within its stated range to avoid inaccuracy or damage.
Example for 20 $\mu\text{L}$ pipette: It will accurately measure volumes between $2$ and $20$ $\mu\text{L}$ .
Examples illustrating reading the volume on different pipettes:
- 20 $\mu\text{L}$ pipette: three digits displayed where the top digit is the tens place, the middle digit is the ones place, and the third digit is the tenths (decimal). For instance, to pipette $15.0$ $\mu\text{L}$ you would set the digits to: tens = $1$ , ones = $5$ , tenths = $0$ .
- 5.5 $\mu\text{L}$ would be: tens = $0$ , ones = $5$ , tenths = $5$ .
- 200 $\mu\text{L}$ pipette: the first digit is the hundreds place, then the tens place, then the ones place, with decimal marks on the tenths (hash marks for the decimal place).
- 125 $\mu\text{L}$ on a 200 $\mu\text{L}$ pipette would read: hundreds = $1$ , tens = $2$ , ones/decimal = indicated by decimal marks; example shows setting for 125 $\mu\text{L}$ .
- 125 $\mu\text{L}$ on a 1000 $\mu\text{L}$ pipette would read: thousands, hundreds, tens with dash marks indicating the ones place.
Important note: Always match the digit scale to the pipette size and use the correct digits to achieve the desired volume.

Hold the pipette resting in your palm with the finger rest positioned over your index finger.
The thumb should comfortably control both the plunger and the ejection button.
Maintaining a relaxed grip reduces fatigue and improves precision over long sessions.

You must attach a tip to the pipette before use; tips prevent liquid from entering the main body and keep the pipette clean.
Change tips every time you pipette a new sample or reagent to prevent cross-contamination.
Two common tip-loading methods:
- If tips come loose in a bag: pick up a tip by the sides and slide it firmly onto the pipette.
- If tips come in a rack: firmly tap the pipette into the rack to secure it onto the tip.
Always ensure the tip is firmly attached and that you are using the correct sized tip for your pipette.
Do not attempt to pipette with a loose or improperly attached tip.

There are two stops on the plunger:
- First stop: a moment of resistance when partially depressed.
- Second stop: fully pressed to the bottom.
Practice pressing to the first stop a few times.
Then push the plunger all the way to the second stop and practice stopping at each point.

To draw liquid into the pipette:
- Push the plunger down to the first stop.
- Place the pipette tip into the liquid.
- Slowly release the plunger to pull the liquid into the tip.
This action draws the correct volume into the tip.

To dispense the liquid:
- Touch the pipette tip to the bottom or side wall of the receiving tube.
- Push the plunger down past the first stop until you feel the second stop to fully dispense.
- Immediately withdraw the tip before releasing the plunger to avoid drawing liquid back up.
If the receiving tube already has liquid, ensure the tip touches the liquid surface to aid mixing when dispensing.
Touching the pipette tip to the side of the tube or to existing liquid helps prevent small droplets from sticking to the tip.
Hold the tube up to eye level to observe exactly where you are dispensing.

To mix a solution by pipetting:
- Place the tip into the liquid.
- Release and push the plunger back down to the first stop several times while the tip remains in the liquid.
To avoid bubbles during mixing:
- Pipette up and down slowly.
- Do not push the plunger past the first stop during mixing.
After mixing, press the plunger to the second stop and remove the tip as usual.

If liquid is accidentally spilled or bubbles form, the liquid can be returned to the bottom of the tube by gently shaking the tube or by briefly spinning it in a centrifuge.

Once you are done, eject the tip over a waste container and attach a new tip for the next step.
Tip ejection ensures no cross-contamination between samples.

Mastery of these skills will enable you to set up reactions, run gels, and explore more experiments in the biology lab.
For pipetting practice activities and more about experiments you can perform with these skills, visit $minipcr.com$ .

Units and conversions:
- $1\,\mu\text{L} = 10^{-6}\,\text{L}$ .
- Pipettes are designed to operate within a specific volume range; exceeding this range reduces accuracy and may damage the instrument.
Reading pipette digits (typical examples):
- 20 $\mu\text{L}$ : digits read as tens, ones, tenths. Example: $15.0\;\mu\text{L}$ corresponds to tens = $1$ , ones = $5$ , tenths = $0$ .
- 200 $\mu\text{L}$ : digits read as hundreds, tens, ones with decimal marks.
- 1000 $\mu\text{L}$ : digits read as thousands, hundreds, tens with dash marks indicating the ones.
Practical tips:
- Always use a properly sized tip and attach securely.
- Change tips for each new sample to prevent contamination.
- Hold the tube at eye level for accurate dispensing.
- Avoid introducing bubbles by slow, controlled pipetting.
- If you need to mix, keep the tip in the liquid while cycling between first stop and second stop to ensure thorough mixing.
Real-world relevance:
- Accurate pipetting is foundational for reliable experiments, such as setting up reactions and preparing samples for gels.
- Proper technique reduces waste, improves reproducibility, and minimizes cross-contamination.
Ethical and practical implications:
- The transcript emphasizes safety, accuracy, and contamination prevention, which align with good laboratory practice and responsible science.