HighPoint/CannonLab:Pipetting Exercise

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Objective

Use pipetters accurately and reproducibly over a range of volumes with liquids of different viscosities

Procedure

1. Prepare:
   1. Prepare the analytical balance
      • Carefully place small weigh boats with water in 2-3 corners of the analytical balance chamber to saturate the chamber with water vapor.
      • Close the chamber.
      • Be careful to avoid spills and clean up any spilled water.
   2. Place a weigh boat on the balance and tare the balance
   3. Familiarize yourself with the pipetters
      • Understand the measurement units and how to adjust the volumes
      • Figure out which tips fit which pipetters
      • Depress and release the plunger several times and become familiar with the two stop points
2. Measure
   1. Set the pipetter to the desired volume
   2. Attach a tip
   3. Draw up liquid
      • Hold the pipetter upright (within 10° of vertical)
      • Depress the plunger to the first stop
      • Stopping at this position reproducibly will effect your precision
      • Place the tip a few mm below the surface of the liquid
      • Gradually release the plunger completely
        • releasing too quickly, or not completely removing pressure from the plunger can both effect your accuracy and precision
      • Lift the tip out of the liquid making sure any drops on the outside of the tip are brushed off
   4. Deliver the sample to its destination
      • Gradually depress the plunger completely (to the second stop)
      • check that all the liquid left the tip, and that none is clinging to the outside of the tip
   5. Close the balance and let it settle
   6. Record the weight of the liquid delivered
   7. Repeat 2 more times
3. Change the volume setting and repeat part 3
4. Use a different size pipetter and repeat parts 3 and 4
5. For one of the pipetters and volumes measured in parts 3-5, repeat the process using glycerol
6. Determine your accuracy
   1. The density of water is 0.997 g/mL at room temp
   2. The density of glycerol is 1.261 g/mL
      • Record the weight delivered and calculate the volume delivered
      • Does the volume delivered match the volume indicated on the pipetter?
7. Improve your accuracy with glycerol
   1. Try cutting off a little bit of the tip with a razor blade
   2. Try pipetting very slowly
   3. Try pipetting into a dish already containing water, and use the water to rinse out the pipette tip