Sciencemadness Discussion Board

pipettes

Cikada - 19-3-2016 at 07:12

Hello, I was wondering about everyone's knowledge of pipettes and their bulbs. Any useful info, and or techniques will be appreciated.
Thank You in advance.

gatosgr - 19-3-2016 at 13:22

Search youtube for videos.

ScienceHideout - 19-3-2016 at 13:59

I LOVE using pipettes in all of my chemistry experiments. I have a good variety:

Beral pipettes are the type that you see quite often: simple plastic droppers that come in boxes of 100 or 500. They cost less than ten cents each. Some people reuse them, to me they are disposable. I only get the 3 mL ones- they're very versatile.

Some Beral pipettes have bellows instead of a bulb. These are expensive, but work well for higher viscosity liquids.

Mohr pipettes and serological pipettes are both graduated glass pipettes that come in many sizes. In my lab I use 1 mL, 5 mL, 10 mL, and 25 mL. There isn't much of a difference. Basically, the only way in which they differ is that the graduations on Mohr pipettes start after the tip, so you will never drain it all the way. Serological pipettes account for the volume of the tip, so you have to blow them out.

Volumetric pipettes are very nice for serial dilution. I have a selection of 1,2,5, and 10 mL ones (I might have bigger if I look in my pipette box, but I'm not sure. I have used ones as large as 50 mL at work). They are VERY precise, and IIRC, you get the most accurate volume if you drain them fully, but don't blow out the last drop.

If you use the glass pipettes, you are going to need a pump. There are several types: there are your typical rubber bulbs of various sizes, there are rubber bulbs with valves built in so you can suck up and drain precisely. There are thumbwheel pumps which are really fast, but I feel that they lack accuracy. You can never get the exact amount unless you pull it off at the top and control it with your thumb. There are the really fancy bulbs with a thumb control lever and a blow out button (I like scilogex ones) and finally the really expensive ones that resemble guns.

There are micropipettes. These are used mainly in biology. I've never used one.

On a regular basis I use pasteur pipettes, long, disposable glass ones both in home and at work. A big box of 200 costs less than $15. You use them with little latex bulbs. You can also shove a piece of cotton inside and use as a filter. VERY versatile!

However, in the lab that I work in, we use syringes much more than anything else!

Herr Haber - 19-3-2016 at 14:39

The only pipettes with bulbs I can think of are not graduated pipettes.
Instead they have a line above the "bulb" which is the mark for 25, 50ml or whatever.
Unless I totally misunderstood the question...

aga - 19-3-2016 at 14:59

What exactly is a 'pipette' ?

I got two 10ml sucky-tube things marked at 0.1 ml intervals.
Also one 25ml one with a bulb that i've used maybe twice.

The 10ml ones have seen more action.

What is the definition ?

blogfast25 - 19-3-2016 at 15:21

Quote: Originally posted by aga  

What is the definition ?


A volumetric device that dispenses a stated volume of liquid at a stated precision (measuring error). E.g. 25 ml +/-0.02 ml.

[Edited on 19-3-2016 by blogfast25]

aga - 19-3-2016 at 15:29

Aha ! So a Burette is basically a Pipette !

I bette there is an -ette family of glassware.

The Beaker.
Un Beakerette.

etc

blogfast25 - 19-3-2016 at 16:01

A burette has more in common with a graduated pipette. Bulb pipettes can only deliver one size volume accurately, contrary to burettes or graduated pipettes.

Metacelsus - 19-3-2016 at 16:23

There are also disposable Pasteur pipettes, used for transferring small volumes of liquids.

ScienceHideout - 19-3-2016 at 16:28

Quote: Originally posted by aga  


What is the definition ?



Here's the real definition according to Hawley's Condensed Chemical Dictionary:
Quote:

pipette (pipet). A slender glass tube open at both ends and having an expanded area at or near the center designed to contain a specific volume of liquid, e.g., 5 cc. Liquid is drawn into the tube by oral suction [!]. Used in transferring measured volumes of liquid from one container to another


Wow, that was an aweful definition. That actually excludes beral pipettes and pasteur pipettes. And encourages mouth-pipetting, which we are all guilty of, but SHOULD NOT encourage.

From what I understand, pipettes do not have to only be volumetric or glass...

Here's the BETTER real official definition according to the McGraw-Hill Dictionary of Chemistry
Quote:

pipet [CHEM] Graduated or calibrated tube which may have a center reservoir (bulb); used to transfer known volumes of liquids from one vessel to another; types are volumetric or transfer, graduated, and micro.


This definition is marginally better, but still implies that pipettes must be graduated or calibrated. Pasteur pipettes and beral pipettes, I suppose, are calibrated in some sense but are still by no means volumetric utensils!

If I wrote a definition of pipette, it would be:
Quote:

pipette A family of glass or plastic tubes of various sizes, ranging from microscale all the way up to 100 mL or more, used to transfer exact or approximate volumes of liquid. Pipettes may be open on one or both ends, depending on whether or not a bulb must be attached. The pipette is used by drawing liquid into it using negative pressure.



Cikada - 19-3-2016 at 17:43

Thanks for all the info!
:)

MeshPL - 20-3-2016 at 03:51

Technically you don't need any kind of bulb/pump for many pippetes. If the level of liquid in the container is high, it will just flow inside the pippete, and if it is low you can use your mouth to pump the liquid.

But you really shouldn't.:P

Deathunter88 - 20-3-2016 at 07:49

Quote: Originally posted by MeshPL  
Technically you don't need any kind of bulb/pump for many pippetes. If the level of liquid in the container is high, it will just flow inside the pippete, and if it is low you can use your mouth to pump the liquid.

But you really shouldn't.:P


That's horrible advice. Try sucking up 98% sulphuric acid into 1ml volumetric pipette without getting any in your mouth...

aga - 20-3-2016 at 10:11

Did an iodine solution once. Tasted awful.

The thing was that there was not enough liquid to draw up, so air got in, sending bubbles (and liquid) all the way to the mouth.

Fortunately there was a lot more potassium chromate & sulphuric acid solution, so it did not happen with that, thank god.

Cikada - 21-3-2016 at 18:27

Yeah using your mouth is not a good idea, for anything dangerous. All though you'll probably be fine most of the time, but it's better to not do it when there is a safe way.

[Edited on 22-3-2016 by Cikada]

MrHomeScientist - 22-3-2016 at 05:42

Pipetting by mouth ranks very near the top in the list of the worst possible things you can do in a lab. Why would anyone in their right mind do that? I'm not guilty of it, because it's insane. Just buy a damn bulb. They aren't straws, and your caustic chemical solution isn't a smoothie.

blogfast25 - 22-3-2016 at 06:13

Mouth aspirating non-toxic liquids like water or very dilute acids/bases is OK though.

Metacelsus - 22-3-2016 at 06:48

Maybe, but it's a bad habit. Just wait until you mistake a flask of something toxic for water.

Mouth Pipetting: Not Even Once
:D

blogfast25 - 22-3-2016 at 06:57

Quote: Originally posted by Metacelsus  

Mouth Pipetting: Not Even Once


I do it all the time, so there! :P