If you calibrate a micropipet with water, is it effectively calibrated for all other liquids (e.g. DMSO, ether, polymer solutions)? If not, how does one go about making trustworthy measurements with micropipets in an atmosphere where they're used by several researchers to measure various liquid solutions.
No and yes, but mostly no!
Whilst Gilson positive displacement pipettes are great, the tips cost a small fortune, so I have until recently been using Hamilton syringes for pipetting solvents. Whilst these are accurate and precise, they are a pain to clean between samples, so I have been experimenting with standard Gilson pipettes to see how well they performed with my main solvent; IPA.
I borrowed a couple of old very 'out of spec' pipettes and calibrated them myself using IPA and they now perform very well indeed. As with most volatile solvents pre-wetting tips (to saturate the atmosphere) and reverse pipetting is a must. With the P1000 set at 1000ul, I get a systematic error of +0.008% (much better than Hamilton syringes) and a relative error of 0.25% (about half as good as a 1000ul Hamilton syringe).
The same pipette used with water under the same conditions gives a systematic error of -1.4% and a relative error of 0.3% - which for me is out of spec. Weirdly however, if the same pipette is used with water in forwards mode, although the systematic error if highish (-0.89%) it is overall within spec. With ACN the results are comparable with those for IPA.
In other words, not only do you have to consider solvent, but you might also have to consider whether you pipette in forwards or reverse mode as this seems to have an effect!