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I'm trying to use a Pasteur pipette for pipetting diethyl ether and regardless of the angle I hold the pipette at, the diethyl ether will automatically start dispensing itself (I am unsure of what this phenomenon is called). I'm sure it's not the rubber bulb since I've been using the same one for pipetting other solvents that don't do this. I've also tried using a different rubber bulb, but to no avail.

Is there any way to prevent this from occurring? If not, is there anyway to mitigate the flow rate of the drips?

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  • $\begingroup$ Low viscocity and high vapor pressure of such solvents makes it a pain indeed. Using an automatic pippet you can reverse pippet (push plunger button all the way down, and dispense only to first check. Also work quickly, deliberately and over short distances $\endgroup$ – Scient Jun 26 '16 at 7:39
  • $\begingroup$ DCM used to be my issue. Either work really quickly if your pipette is graduated or ditch the pipette and use a polypropylene plunger syringe (not the rubber ended ones, fine for bio, rubbish for wet organic chemistry ). I also used to overfill the (plastic) pipette and let it drip to roughly the correct volume, then transfer. Depends on your application. $\endgroup$ – Beerhunter Jun 26 '16 at 8:00
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Usually I avoid pipetting diethyl ether because it can be a bit annoying, but recently I've realized there is a very simple technique which markedly increases ease of transfer (though admittedly I've been using it mostly for DCM). All you have to do is saturate the interior of the pipette with the vapour of the low-boiling solvent before performing the transfer.

The problem arises because the low-boiling solvent will quickly (but not instantly) evaporate into the partial vacuum inside the pipette after pulling the solvent. If you try to transfer the liquid while it's still evaporating significantly, the large volume change from the phase transition will push the liquid beneath through the pipette exit.

So how do you get around this problem in practice? Using the pipette, simply pull and dispense the solvent a few times in succession over 5-10 seconds inside the outgoing vial. Then pull what you need and transfer. In my experience this greatly mitigates dripping. If you're not too slow between transfers, you can get away with doing this only once, at the start.

Other things which can be done to help:

  • As mentioned in the comments, avoid dragging the filled pipette over a large distance. Keep the outgoing and ingoing vials right next to each other, at about the same level.
  • Pull a little bit of air into the pipette, keeping it between the exit and the solvent. This gives you a small time buffer before it drips out.
  • If you have a steady hand, keep very gently pulling air while you move the pipette between vials, matching the speed at which the liquid tries to drip out. This can be somewhat fiddly, so train to get a feel for it.
  • Don't fill the pipette to its maximum capacity on each transfer; do more transfers, each with less volume.
  • There's always a drip left on the very tip of the pipette, and that can easily fall. To avoid it, contact the remaining drop onto one of the outgoing vial's walls above the surface of the liquid, then pull a little bit of air into the pipette, sucking the last droplet along and leaving the tip dry.
  • Practice.
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