Hexavalent - 28-3-2012 at 08:31
So, the technician was spring-cleaning the lab stockroom yesterday and gave me a load of unneeded glasswear (yay!), including several 1,2,5 and 10 ml
volumetric and Mohr pipettes. However, I do not have appropriate bulbs or pumps for them . . .
. . .my question is, can propiettes and proper pipette pumps be modified to suit different bores of pipettes?? On eBay, many different sizes of the
latter are sold, suggesting that you need one per volume of pipette, ie one for 2ml ones, one for 5ml ones etc.
Thanks
bfesser - 28-3-2012 at 09:03
This is an image I found on Google of the exact bulb I use. It's cheap, and it's all you'll ever need. I <em>hate</em> pumps (as they
tend to leak), and bulbs with valves are just an unnecessary complication and a pain in the ass. This simple bulb has served me well for many years
of use. Hope this helps!
<img src="http://www.chem.ucla.edu/~gchemlab/pipetbulb.jpg" width="200" />
[edit]
I purchased mine on eBay, but the seller no longer has them. Here's a <a href="http://www.labdepotinc.com/Product_Details~id~344~pid~12714.aspx"
target="_blank">link to a supplier</a>, but I'm sure you could find better. Also, in my experience, thin nitrile gloves tend to get caught
and torn in the thumb wheels of some pumps. I have a few pumps, but I never use them.
[Edited on 3/28/12 by bfesser]
Dr.Bob - 28-3-2012 at 09:11
Most volumetric pipettes have the same diameter tubing at the top, so any rubber bulb will fit on them. But a small bulb (say 2ml) will not work to
suck up 25 ml into a pipette. The one above will do fine for up to about 25 ml, but is only as accurate as your eye to hand coordination allows.
Being challenged in that area, I use other tools if accuracy counts.
The second most simple tool is a manual Pipet Filler bulb like the one below. You simple squeeze the bulb (and top valve) to create a vacuum, then
press the fill valve to suck the liquid up and then press the flow valve to dispense it, and manually stop the flow by releasing the valve. They
work OK for crude volume measurements, but are hard to make accurate or repeatable. But they are cheap, from $5-20 and up.
https://us.vwr.com/store/catalog/product.jsp?catalog_number=...
Now if you want to pipette the same volume repeatedly without variation, there are mechanical pipettors of many types that allow you to use a syringe
type device to suck and dispense either a fixed or adjustable volume in an accurate and repeatable manner. Some are even electric or battery operated
and can squirt all day. They range from a few bucks to $1000+. Even within that category there are many different types and styles for different
uses. Some examples are The Eppendorf Repeater, Gilson and Rainin pipettors, and multichannel ones that do 1, 6, 8, 12, or 96 pipettes at a time.
[Edited on 28-3-2012 by Dr.Bob]
bfesser - 28-3-2012 at 09:30
You need a stiffer rubber bulb for larger volumetric pipettes, as it has to raise more liquid <a href="http://www.youtube.com/watch?v=8F4i9M3y0ew"
target="_blank">against gravity</a> <img src="../scipics/_ext.png" /> and the pressure differential. You can, however, use such a bulb
for any volmetric or measuring pipette. I've used the one pictured for .2 mL measuring pipettes calibrated to 0.01 mL all the way up to a 100 mL
volumetric pipette. For the larger ones, you simply suck, swap bulb & finger, squeeze air out of bulb, swap bulb & finger, repeat as needed.
<strong>Dr.Bob</strong>, as the <a
href="http://www.medindia.net/news/Famous-Adage-Practice-Makes-Perfect-Receives-Scientific-Backing-31584-1.htm" target="_blank">adage</a>
<img src="../scipics/_ext.png" /> goes, <em>'Practice makes <del>perfect</del> <a
href="http://en.wikipedia.org/wiki/Accuracy_and_precision" target="_blank">[precision/accuracy]</a> <img src="../scipics/_wiki.png"
/>'</em>.
[Edited on 7/9/13 by bfesser]
unionised - 28-3-2012 at 12:52
At work I use a pipette filler and swear about it: at home I pipette by mouth.
However I can't honestly recommend this approach.
Hexavalent - 29-3-2012 at 11:06
Really? Everything, all reagents?
Endimion17 - 29-3-2012 at 12:09
As for me, these rules of thumb apply:
propipette for:
- larger amounts (>10 ml) of concentrated, corrosive acids
- any amounts of heavy metal solutions
mouth for:
- small amounts of mentioned acids and poisonous organic solvents (benzene, methanol, ...)
- larger amounts of dilluted acids
- any amount of weakly poisonous organic solvents (ethyl acetate, hexane, acetone)
I'm not a vacuum pump and I do have brain and a set of eyes, so there's hardly any danger of getting the stuff into mouth.
Vapors entering the mouth are of concern, but that danger appears when the volumes are larger, meaning the fluid meniscus in the pipette is bigger.
Precise pipettes are narrow.
Hexavalent - 29-3-2012 at 12:22
I could never bring myself to, essentially, sucking on a piece of lab glassware. Even if it seems clean and has been rinsed thoroughly, I always
thought that lab glassware can still hold minute amounts of heavy metals, known for being cumulative . . .
way2jordan - 16-8-2012 at 23:32
Yes you may but there are lots of cheap and different size burettes are available in the market. A Volumetric pipette is a tool for measuring
precise volumes of a liquid. Pipettes are typically long tubes, open on both ends, marked to contain (or deliver) a certain volume of liquid.
--------------------------------------------------
pipette 
Hexavalent - 17-8-2012 at 00:32
Not necessarily; there are volumetric pipettes available, which, as you say, deliver only one volume of liquid, and graduated pipettes, which function
like a burette or a graduated cylinder in the sense that they can measure many volumes within a range, e.g. 1-10ml.
Historically, the accuracy of a graduated pipette was not as good as that of a volumetric pipette; however, with improved manufacturing methods, the
accuracies listed by the manufacturer can equal volumetric pipettes.
Two types of graduated pipettes exist:
-Mohr pipettes or drain-out pipettes have a 0ml mark before the start of the conical end, which is a dead volume.
-Serological or blow-out pipettes have no 0ml mark as that corresponds to an empty pipette.
Graduated pipettes have +/- tolerances that range from 0.6% to 0.4% of the nominal volume when measured at 20C. They are manufactured according to ISO
specifications for accuracy and the arrangement of the graduations. A-grade pipettes are more accurate than B-grade pipettes, for example, yet an
A-grade volumetric pipette is the most accurate of all.