Pipetting Skills Essentials

Pipetting Goals

Learn to operate micropipettes and serological pipettes, choose the appropriate instrument for specific volume measurements, and perform accurate metric volume measurements and calculations.

Instrument Overview

Molecular biology requires measuring small volumes using two primary instruments:

  • Micropipettes: For accurate transfers of 1−1000 μl1-1000\ \mu l (e.g., P20, P200, P1000 models).
  • Serological Pipettes: For accurate transfers of 1−50 ml1-50\ ml.
Micropipettor Selection and Usage

Each micropipettor model has a maximum capacity (e.g., P1000 for 1000 μl1000\ \mu l). The instrument is calibrated and most accurate when set within 10%−100%10\%-100\% of its maximum capacity; avoid setting outside this range to prevent damage. The digital volume indicator shows the set volume, where the top position corresponds to the first digit of the model's designation. Disposable tips (clear for P20/P200, blue for P1000) must be used and changed between solutions.

Pipetting Accuracy and Error Detection

Successful pipetting requires precision. Common errors include over-measurement (fluid left in tube) and under-measurement (air space in tip). Accuracy can be checked by weighing dispensed distilled water, using its density of 1 g/ml1\ g/ml. Measurements should be within 5%5\% of the expected mass. If errors occur, re-practice technique.

Volume Conversions

Key metric volume conversions include:

  • 1 ml=1000 μl1\ ml = 1000\ \mu l
  • 1 L=1000 ml1\ L = 1000\ ml
    Thus, 4 ml=4000 μl4\ ml = 4000\ \mu l and 4 ml=0.004 L4\ ml = 0.004\ L.