problems with pipetting - (Mar/02/2008 )
Hello!
I was wondering whether anyone has a problem with pipetting using Pipetman pipettes, in which the pipette plunger turns as you are pipetting-and thus might change the set volume a little? Especially when u're pipetting the same volume of eg. sample buffer into multiple tubes, do you guys check that the volume is set correctly in between each tube? i've been doing that and it's extremely time consuming....hope i'm just being paranoid... 
It happens sometimes, but typically it means you're not pressing down on the centre of the plunger. Make sure your thumb is directly over the centre.
I was wondering whether anyone has a problem with pipetting using Pipetman pipettes, in which the pipette plunger turns as you are pipetting-and thus might change the set volume a little? Especially when u're pipetting the same volume of eg. sample buffer into multiple tubes, do you guys check that the volume is set correctly in between each tube? i've been doing that and it's extremely time consuming....hope i'm just being paranoid...
If you think there is a problem, then th only TRUE way is to:
Get a BALANCE
Pipette the same volume 20-30 times and SEE on the balance any errors in volume
When you are first in my lab, pipetting technique is one of the most important variables. ACCURACY AND PRECISION can only be measured by using a balance.
GILSON'S are king in my opinion.
Kindset regards
Rhombus
If the pipette is good, this should not be a problem. But some pipette brands are crap and this can happen. Don't use/buy Rainin pipettes.
Gilson is the best !!!
Gilson is the best !!!
Hmm..didn't know that. All I've ever see in any lab is Rainin. I'll keep that in mind.
I was wondering whether anyone has a problem with pipetting using Pipetman pipettes, in which the pipette plunger turns as you are pipetting-and thus might change the set volume a little? Especially when u're pipetting the same volume of eg. sample buffer into multiple tubes, do you guys check that the volume is set correctly in between each tube? i've been doing that and it's extremely time consuming....hope i'm just being paranoid...
This happens to me on occasion (once a month or so) using my lab's Finnpipette-brand micropipetters. As swanny said, usually it's because my thumb wasn't centered on the plunger and depressing the plunger caused it to rotate a notch. With the Finnpipettes it's rather noticeable, and since it's on the downstroke anyway it's not a problem as long as I reset the volume immediately.
If you're having lots of problems with your pipettes resetting when you depress the plunger, you should look into having the pipettes serviced. How long has it been since they were serviced and calibrated? In the meanwhile, you should definitely be checking that the volume is correct until your problem is resolved.
You can always use the electronic pipetter which is very easy to use and pipette exact volumes.
Thanks evereyone, I apprieciate all your replies! I'll def look out that my thumb's on the middle of the plunger while i'm depressing it, and will probably do a test on a balance to check for pipette accuracy if there's still a problem. The pipettes are serviced once a year, so I thought they should be fine...
Thanks again!
madpie