These troubleshooting steps will help you in the case that you've been experiencing any of the following issues:
- Tips unexpectedly dropping
- Pipette not aspirating properly
- Uneven aspiration across channels of a multichannel
Step 1: Make sure multi-channel pipettes are mounted level
Multi-channel pipettes are especially sensitive to tilt. When attaching them, some extra care is needed to make sure they are perfectly straight.
When attaching a multi-channel pipette:
- Leave the 3 screws slightly loose.
- Use your hand to gently and slowly pull the multi-channel pipette all the way down to the OT-2's deck.
- Wiggle the pipette so that all 8 of its nozzles touch the deck at the same time.
- While holding the pipette down, tighten the 3 screws.
A tilt with a difference of less than 0.15 mm between ends is acceptable. (0.15 mm is somewhere between one and two sheets of typical printer paper.)
Step 2: Ensure there is no issue with the pipette
The first step to take is to ensure there is no issue internally with the pipette. To do this, take the following steps.
- Upload a protocol that simply picks up tips and transfers a liquid
- Pause the protocol directly after tip pick up
- Use your hands to firmly secure the tip onto the pipette stem (do this for each stem if using a multichannel)
- Resume the run
- If this solves the problem, move onto the next step. If the issue persists, contact support with details of the issues and the steps you've taken.
Step 3: Adjust parameters of pick up tip function
Using the function pick_up_tip(), you can adjust two parameters: presses and increment. These parameters are designed to make the function customizable to find the ideal configuration for the function to work properly.
- "Presses" refers to the number of times the pipette moves down with force on the tip. By default, it moves down three times.
- "Increment" refers to the distance the pipette will travel downward in mm for each press. By default, the first press moves down 3.5 mm (this cannot be changed) and subsequent presses move down 1 mm (this can be changed).
These parameters can be adjusted with the following syntax (assuming "pipette" is the name of the pipette): pipette.pick_up_tip(presses=5, increment=0.5)
The best method is to test different parameters until you find a configuration that you can rely on. The default number of presses and increment distance will result in 4.5mm total distance travelled. The same distance will be travelled in the example above, but may result in a more reliable pick up.
**NOTE** also test that drop tip functions effectively with the parameters you pass for tip pick up
Step 4: Increase Pick Up Current
Use pipette.set_pick_up_current(0.5) to increase the force applied during the function. The default current is 0.5 amps - the best method is to test in increments of .1 until you find a current that works more reliably. This works best in unison with the method above.
**NOTE** the max current that should be applied is 1.2 amps and the pipette lifetime has only been tested with the default current