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
- Prepare:
- 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.
- Place a weigh boat on the balance and tare the balance
- 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
- Prepare the analytical balance
- Measure
- Set the pipetter to the desired volume
- Attach a tip
- 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
- 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
- Close the balance and let it settle
- Record the weight of the liquid delivered
- Repeat 2 more times
- Change the volume setting and repeat part 3
- Use a different size pipetter and repeat parts 3 and 4
- For one of the pipetters and volumes measured in parts 3-5, repeat the process using glycerol
- Determine your accuracy
- The density of water is 0.997 g/mL at room temp
- 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?
- Improve your accuracy with glycerol
- Try cutting off a little bit of the tip with a razor blade
- Try pipetting very slowly
- Try pipetting into a dish already containing water, and use the water to rinse out the pipette tip