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I work in a lab where all the pipettes are shared. We often have visiting students who come and use the pipettes for a short project. So when I work with them, they might have been handled by other people several times since I last used them. This leads me to worry that they might have been mishandled, or become less accurate somehow.

How do I clean and calibrate pipettes? And how often do I need to do it?

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2 Answers 2

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How often you should calibrate your pipettes depends on the tolerances of your application. For some applications, like quantitative PCR setup, one may care a great deal; for general lab work, one can probably be less particular. You can get a sense of how accurate your pipettes are by pipetting DI water onto the platform of a sensitive (and calibrated!) balance. Comparing the random and systemic error you get while doing that over several trials to the specifications published by the manufacturer will give you a good idea of whether pipette calibration will help and help give you a sense of how much you care. Note also that the error may vary with the volume; you should test error over the entire volume range you intend to use the pipette for.

How to clean and calibrate pipettes is specific to each design. Some pipettes, like Gilson's, are not intended to be calibrated by the user. Others are. The pipette user guide published by the manufacturer should tell you.

For some demanding applications, even well-calibrated and well-handled micropipettes may not be sufficiently accurate. In particular, I've made standard curves by serial 10-fold dilution for quantitative PCR both a) relying on my micropipettors to be correct and b) trusting pipettes only to get me into the right ballpark, and intentionally undershooting and correcting volumes with sequentially smaller pipettes until the reading on the balance is correct, if that's at all clear. In both cases I was using 900 ul of diluent and 100 ul of the previous dilution, which I feel are comfortably large volumes to handle. I found that the latter curve gave me noticeably better regressions.

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Just a small note that hasn't been mentioned elsewhere. Pipettes remain in calibration longer when reset to their maximal volume when not in use. This is because it allows the spring (or other compression device) to relax fully and not be forced to stay in a compressed position. This is an oversight I see in labs all the time, and something I always add to SOP's. –  Atl LED Jul 9 '13 at 14:09

When doing a recent investigation into methods of quantitatively determining the concentration of aspirin in solution I found these procedures helpful. They are a rough guide; design and procedure will vary by model. It may be wise to check the manual that came with it, however in summary:

Calibration

  1. Performed at least once per week
  2. Performed in a room of the temperature indicated on the glassware (or at the very least in a room where the temperature will not fluctuate during the calibration).

For example a pipette I was using was a 10ml graduated, the procedure for which was:

Rinse the 10 mL pipette with 10 mL of water. Pipette 2 mL into a tared vial containing water on a 2-place balance. Document the weight. Set the pipette to 5 mL, pipette 5 mL into the vial and document the weight. Set the pipette to 10 mL, pipette 10 mL into the vial and document the weight.

However procedures are given in the linked document for pipettes down to 100μL. Then compare the values from the mass with the acceptable values in the appendix. A calibrated pipette will give ±1% of the mass indicated in the appendix, for example the pipette I described above:

  1. 1.98-2.02 g
  2. 4.95-5.05 g
  3. 9.90-10.1 g

Cleaning can be achieved by pipetting up and rinsing with distilled water (in my case) or more likely for your case 'nanopure' water.

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