pipetting sticky solutions - (Dec/14/2007 )
Hi all,
Can anyone relate to the difficulty in pipetting viscous aqueous solutions like methylcellulose for cell assays? Do you know of any products like specialized pipets to reduce retention/adhesion of the material by the pipet? Would you want to use such a thing? Thanks,
DanG
I believe there are positive displacement pipets specifically for this purpose. They have a plunger which contacts the material and pushes it out of the tip. I think they use disposable tips which include the plunger.
cut the tip with a sterile blade to widen it.
If you have to pipet it often, it could be interesting to dilute it slightly.
For example, I prefer to use a 80% w/v glycerol solution instead of pipeting each time this viscous glycerol (of course you have to recalculate the volume to use, according to the density of glycerol, however it' easier to weight glycerol and then to adjust the right volume of water to get a 80% solution than to pipet an exact volume)
I don't know if it helps you
For example, I prefer to use a 80% w/v glycerol solution instead of pipeting each time this viscous glycerol (of course you have to recalculate the volume to use, according to the density of glycerol, however it' easier to weight glycerol and then to adjust the right volume of water to get a 80% solution than to pipet an exact volume)
I don't know if it helps you
Positive displacement pipette all the way. I've not found any other approach that works better.
Ginger
i agree that positive displacement pipetting is the way to go for viscous solutions but...
you can also try reverse pipetting. you fill the pipette with the blowout and then expel to the normal fill. this works pretty well but if you are pipetting something very viscous (eg-glycerol, triton, tween, etc) then you have to expel slowly.
We usually cut the tip. I personnaly do many "up and down" to "wash" the interior of the tip and try to get a volume as exact as possible.
The problem with cutting the tip is that it reduces the volume you dispense. So do you cut only a small amount off the tip to maintain the volume, or do you cut off more to make the dispensing easier, but with less accuracy? I'd go with positive displacement or reverse pipetting if you don't have the positive displacement. And the idea of predilution is good, too.
How could the volume be smaller?
Of course, we don't cut the tip if we are to pipet 1000ul with a p1000.. If we are to do so, we go for two shots of 500 ul. And positive displacement are not something we can afford 
Anyway, the predilution is the best possible way. But you'll have the same problem with the initial prelevement of the solution, hehe!
Of course, we don't cut the tip if we are to pipet 1000ul with a p1000.. If we are to do so, we go for two shots of 500 ul. And positive displacement are not something we can afford
Anyway, the predilution is the best possible way. But you'll have the same problem with the initial prelevement of the solution, hehe!
In normal pipettes, the volume delivered is the tip volume plus the volume in the barrel. Logically, if you cut the tip, you reduce that component of the equation, therefore less liquid delivered.