Which Pipettes to Use? - (Jul/01/2010 )

Hi everyone!

Just a quickie. The lab I am in measures the quantity of acetic acid and propionic acid in samples by G.C.

At the moment we are trying to accurately pipette the quantities using glass pipettes and fillers, which I hate, and find to be almost impossible to get spot on everytime. When I queried this, I was told we can't use mechanical pipettes because the chemicals we use 'screw them up'.

We use;

acetic acid
propionic acid
valeric acid

all diluted in a stock mixture of orthophosphate:diethyl-ether. Do I HAVE to use glass pipettes?

Also, the stock solutions we make up are kept in the fridge for 1 month, which I think is a bit too long with stuff like diethyl. Any thoughts on this?

Thanks for any help!!

Scoob00,

What about a repeater with a syringe? The acid will never touch the pipetter itself.

regards,

lab rat

Hiya,

Thanks for your reply! Sorry to sound dense, but whats a repeater with a syringe?

Cheers!

scoob00 on Thu Jul 8 12:31:20 2010 said:

Sorry, I haven't been around in a while. Here's a link (I'm not endorsing either the brand or the vendor.)
http://www.thomassci.com/dd8bc665-2b1a-423a-b95e-f9ca09bdd1a1/_/Repeater-Plus-Pipettor/

LaRa is right. I think you could use any positive displacement pipette (the repeater is basically a positive disp) in which the piston is in the tip, so the liquid is never in contact with any permanent part of the pipette.

This one is from Gilson, they have some good explanation on their working
http://www.gilson.com/en/Pipette/Products/53.224/Resources.aspx?resourceTypeId=1

Actually, part of the problem is gases evaporating off the surface of the acid, which then corrode any metal parts and deplastinate the plastics.

If you are worried about small volumes, use a small glass plunger hamilton syringe, or make up a bigger volume.

Hi Scoob00, Just saw this new kind of tips in a box of free test samples that I got last day and thought of your needs!

They are called Solvent safe carbon filter pipet tips...never used them myself...they claim its meant for acids, organic solvents etc

http://www.mbpinc.com/ASP/products.aspx?query_TipId=85

yeah, the vapours would still be a trouble no matter whatever you use!