Pipette Accuracy Activity

Printable version: calibrate_1.04.v1

Objectives The purpose of this lab is to practice pipetting and test your accuracy. You’ll also gain some experience working with the scientific scale.

Materials

  • – Distilled water
  • – Food coloring
  • -Heavy absorbent paper such as watercolor paper,
  • filter paper, or paper towel
Equipment/Labware

  • – Micropipettes
  • – Pipet tips
  • – Scientific scale
  • – Wax paper or weigh boats

Pure water weighs 1 gram per milliliter, which makes it very easy to test your pipetting skills. If you pipet 1000 μl onto the scale, it should weigh 1 gram or 1000 μg. Micropipettes usually come in four sizes: 2 μl, 20 μl, 200 μl, and 1000 μl. Micropipettes generally don’t need to be calibrated (although they should occasionally be serviced by a trained technician), but proper pipetting skills and the correct choice in pipet size can help your accuracy.

Rule of Thumb: choose the pipet that has the maximum volume closest to the volume you want.

Quick Quiz (answers below) What pipette would you use to measure out

  1. 15 μl
  2. 100 μl
  3. 750 μl
  4. 1400 μl

Answers: 1) use the 20 μl, 2) 200 μl, 3) 1000 μl, 4) there are a few different ways, 1000 μl + 200 μl + 200 μl; 1000 μl + 400 μl , or use the 1000 μl to measure out 700 μl, twice. If measuring out a volume over 1000 μl, it’s easier to divide the volume in half and measure the same amount out twice instead of re-setting the pipet.

Pipetting Activity

  1. Cover the weigh-pan of the scale with something waterproof such as a piece of parafilm, a piece of plastic, or a plastic weigh-boat. Tare the scale so it reads 0 with the parafilm on it.
  2. Pipet the volumes in the Table using the micropipette indicated and record the weight of the water drop.
  3. After each measurement, soak up the water with a paper towel and tare the scale.

Measurement table: Use the different pippetor sizes to measure out the volume in the first column. Record the weight of each drop in the table

Pipettor sizes àVolume ↓ 20 μl 200 μl 1000 μl
17 μl
100 μl
192 μl
847 μl
Use all three sizes to measure out 1222 μl
1222 μl
Use just the 1000 μl to measure out 1222 μl
1222 μl
Try a few more variations and write down your results. Be sure to make a note of which pippetors you used.

Pipetting activity 2:

  1. Put a few drops of food coloring in different containers of water
  2. Using the 20 μl pippetor, pipet drops of colored water onto thick paper
  3. Practice keeping droplets of the same volume the same size on paper
  4. “Draw” patterns in different colors and different volumes