March 04, 2024, 07:40:50 PM
Forum Rules: Read This Before Posting


Topic: Can you calibrate micropipets for for all liquids  (Read 1248 times)

0 Members and 1 Guest are viewing this topic.

Offline PSbP2VP/NMP+PtCl62-

  • New Member
  • **
  • Posts: 8
  • Mole Snacks: +0/-0
Can you calibrate micropipets for for all liquids
« on: March 12, 2023, 06:19:12 PM »
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.

Side note: I have a general mistrust of pipets as volumetric measurement tools (PTSD from having to repeat weeks of ICP-MS measurements in gradschool) and never really use them for measurements, so I've never bothered to have my micropipet set calibrated (the balance gets biannual professional calibration and business class treatment in the lab).

Offline DrCMS

  • Chemist
  • Sr. Member
  • *
  • Posts: 1296
  • Mole Snacks: +210/-81
  • Gender: Male
Re: Can you calibrate micropipets for for all liquids
« Reply #1 on: March 13, 2023, 06:20:00 AM »
If you calibrate a micropipet with water, is it effectively calibrated for all other liquids (e.g. DMSO, ether, polymer solutions)?

No it is not.  If have calibrated with a liquid with a particular density/viscosity/surface tension and then use a liquid that does not have exactly the same density and viscosity and surface tension it will not dispense the same calibrated volume.

Offline rjb

  • Full Member
  • ****
  • Posts: 121
  • Mole Snacks: +17/-0
Re: Can you calibrate micropipets for for all liquids
« Reply #2 on: March 27, 2023, 07:05:51 PM »
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!

R

Sponsored Links