6 replies to this topic

[scoob00]

Good afternoon!

I have a quick question about mechnaical pipettes please. Basically, is there any reason they wouldn't work with any of the following chemicals;

Diethyl ether
Orthophos. acid
Acetic acid
Propionic acid
Valeric acid

At the moment I'm using glass pipettes and fillers (time consuming, inaccurate, bane of my existence) because apparently when they tried using gilsons before, these chemicals 'screwed them up'.  I have used diethyl fine with them before at a previous lab which is basically the diluent of the other acids listed.

Any advice would be very, very much appreciated!!

Cheers.

[mdfenko]

i've used pipets for these (except for the ether). you have to be careful to prevent the acid from entering the barrel or it will damage the pipet.

ether will drip out of the tip so you have to work quickly or use a different device.

[hobglobin]

You might try a positive displacement pipet, such as Gilson Microman or Eppendorf Biomaster

[bob1]

The vapour off glacial acetic acid will etch/corrode the metal piston on a Gilson pipette, which affects how the pipette measures.

[hobglobin]

bob1, on 12 January 2011 - 02:47 PM, said:

The vapour off glacial acetic acid will etch/corrode the metal piston on a Gilson pipette, which affects how the pipette measures.

That's why a positive-displacement pipet uses not standard pipet tips, but disposable piston-tips. I.e. the piston has direct contact with the sample and is replaced by a new one with every sample. The pipet itself has no contact to the sample. Additionally advantage is that there's no air cushion between the disposable piston and the sample. Therefore the aspiration force remains constant, unaffected by the physical properties of the sample (good for samples with insufficient surface tension or high viscosity). I guess the main disadvantage is the higher price of every piston compared to usual tips.
Here's a pdf for the principle.

[Zymech]

Ive used a research plus pipette for most of these, -I never had any problem.

just pipette a little just in case, as others have said, some acids can be corrosive to the inner parts of the pipette.

[bob1]

hobglobin, on 13 January 2011 - 06:13 AM, said:

bob1, on 12 January 2011 - 02:47 PM, said:

The vapour off glacial acetic acid will etch/corrode the metal piston on a Gilson pipette, which affects how the pipette measures.

That's why a positive-displacement pipet uses not standard pipet tips, but disposable piston-tips. I.e. the piston has direct contact with the sample and is replaced by a new one with every sample. The pipet itself has no contact to the sample. Additionally advantage is that there's no air cushion between the disposable piston and the sample. Therefore the aspiration force remains constant, unaffected by the physical properties of the sample (good for samples with insufficient surface tension or high viscosity). I guess the main disadvantage is the higher price of every piston compared to usual tips.
Here's a pdf for the principle.

I know about positive displacement pipettes, I was just explaining for those who didn't know about conventional pipettes...