Pipette Issues when using pipette gun - (Jul/08/2014 )

So today I was using the pipette gun, everything going normal, everything pipetted normally, until I got to the TPA. I used a 2ml pipette, but the TPA just didn't want to be sucked up! The level kept dropping until the liquid went back to the container it originally was in. I had warmed it up for 1 hr before I started pipetting, so I don't think this is an issue of it being too cold or something.

Any ideas on why this is happening?

Thanks.

Did you try changing pipettors and/or pipette?  Occasionally I will find a single pipette that has a crack, usually around top, such that you can't easily see the crack, but the pipette won't hold a vacuum and the liquid drops out.

What bob said is the most probable solution, there are really sometimes pipettes with cracks. Alternatively I've also seen problems with the pipette not being stuck correctly into the gun, with the same result that it is not tight an the liquid keeps dropping out. We even had a whole pipette series (50 ml) which would never close tightly even though they were meant to fit the gun model, and everything kept dropping out.

bob1 on Tue Jul 8 22:57:03 2014 said:

Did you try changing pipettors and/or pipette?  Occasionally I will find a single pipette that has a crack, usually around top, such that you can't easily see the crack, but the pipette won't hold a vacuum and the liquid drops out.

I tried a different pipette on something else (the cell culture from the tube) to put it in petri-dish and the same problem happened... maybe both pipettes had issues?

Tabaluga on Wed Jul 9 13:03:14 2014 said:

What bob said is the most probable solution, there are really sometimes pipettes with cracks. Alternatively I've also seen problems with the pipette not being stuck correctly into the gun, with the same result that it is not tight an the liquid keeps dropping out. We even had a whole pipette series (50 ml) which would never close tightly even though they were meant to fit the gun model, and everything kept dropping out.

I don't think it was that the pipette wasn't stuck correctly into the gun, since I've done that mistake before and it doesn't look like it... while sucking up the TPA, the pipette misted up rather than seeing bubbles or just having a difficult time getting the substance into the gun.

Like, it would suck up the TPA, but then after a while slowly go down.

Hm. I think perhaps TPA is an alcohol it had some effect on the pipette?

Though I've no idea what TPA is, the reason might me the high vapour pressure (or was it low surface tension?) of the liquid which makes it dropping out of the pipette (similar to organic solvents like hexane). Here usually a "positive displacement pipette" helps.

But since usually they seem not that common, you may suck in a bit more (e.g. you can estimate how much liquid is lost during pipetting and add this) and then pipette fast. But this is only a good idea if the volume don't have to be that exact.

It could also be that it is dissolving your pipette - the mistiness might be the result of this especially if the mist doesn't clear and is in the region where the liquid was.  Use a glass pipette if this is the case.

so as it turns out, it was an issue with the pipette gun. somehow a piece of cotton had gotten stuck in there. after removing it, the pipetting works fine now. :)