[NewSoul]

Hi guys.  This might be a bit of a silly problem, but I can't for the life of me pipet anything!  I just can't get the liquid to fill up into the tube.  I can get the liquid to rise for a short time, but then I cannot get it any further.  We use the typical pipets with separate rubber pipet-filler bulbs (pic below).  I've tried modifying the speed in which I release the bulb with no luck.  Can any of you guys give me some tips?  Thanks.

[curiouscat]

Try a larger bulb? Check for air leaks?

[Arkcon]

Another option is to overfill the pipette with the bulb, then remove the bulb, and rapidly put your finger  (gloved please!) over the end.  You can then gently release to the level you want.  The glass end is very smooth -- so it makes a good glove seal, but its always deliberately imperfect, if you rotate the pipette under your fingertip, the seal breaks and reforms, and you can dispense less than 1 ml as you rotate.  Keep practicing, the amount of control you can achieve is high, for very little practice.

[NewSoul]

Try a larger bulb? Check for air leaks?

We are all always given the same type of pipet and bulb in my lab class, but I will try to check for air leaks.  I might have to make due with what I have.

Another option is to overfill the pipette with the bulb, then remove the bulb, and rapidly put your finger  (gloved please!) over the end.  You can then gently release to the level you want.  The glass end is very smooth -- so it makes a good glove seal, but its always deliberately imperfect, if you rotate the pipette under your fingertip, the seal breaks and reforms, and you can dispense less than 1 ml as you rotate.  Keep practicing, the amount of control you can achieve is high, for very little practice.

Thanks for the tips in getting an accurate measurements.  My main issue is actually the process of drawing the liquid into the pipet with the bulb.

[eazye1334]

I used to have trouble with this too. Because I haven't seen you do it, it's hard to say where you might be having a problem, so forgive me if I'm off.

Here's what I do to fill, say, a 50 mL pipet.

1. Squeeze bulb
2. Shove it onto the end of the pipet
3. Put pipet tip into the working solution
4. Release bulb
5. If it stops fillling short of what you need, do the following:
     - Keeping the pipet tip in the solution, pull the bulb off of the pipet
     - Squeeze the bulb again
     - Quickly shove it back onto the pipet
     - Release bulb and allow it to fill again, repeating until you have enough

Is this the process you're using? Does it only happen with larger pipets or do you struggle to fill up smaller ones too, say 5 mL?

[NewSoul]

Yes, I have trouble filling small pipets as well.  The liquid will often hardly move at all when I slowly release the bulb.  I suspect curiouscat is right in that it's an air leak, but is there any way for me to prevent/fix this with what I have?

[eazye1334]

I would say yes, that sounds like a leak somewhere then. Make sure it's really pushed onto the back end of the pipet. It might not be sealing right at that point. Even if it were a small hole in the bulb it would fill up some, so I wonder if the rubber section is not sealing correctly.

[Arkcon]

If the bulb is worn out, it will often leak.  Unless you're really not using it correctly.  We can't figure these things out via TCP/IP.  If you have take 10 ml pipette, and you squeeze the bulb, shove the open pipette end in firmly, insert the point into a beaker of water, and release the bulb, are you saying that you don't get a pipette full of water?  'Cause that's a useless bulb.  You can try to tighten seals, or cover leaks, often Parafilm is used for this purpose.  But if the bulb really doesn't work, the instructor should give you a new one, if they can't use this one.  Note: as you can see from what eazye1334: wrote, these bulbs come in different sizes, even if you can fill a 10 ml pipette just fine, the same bulb won't fill a 50, or 150 ml pipette with one squeeze.

[curiouscat]

Try swapping a bulb with someone else. See if that works any better.

Will tell you if it's you or the bulb that's the problem.

[NewSoul]

I must have been using a worn out bulb for the past several lab classes then.  In my most recent class I had absolutely no issues pipetting.  Go figure.  :/