Chromatography Forum

Hello,

I have a question about the preparation of the mobile phase.
In all the articles that I have read the proportion of solvent in the mobile phase is always 100% for example 70/30 (ACN / MeOH) so for a liter 700 ml of ACN + 300 ml of MeOH are mixed to obtain the mobile phase.
Today I saw in an article that the mobile phase has a composition of 70/20/15 (MeOH / H2O / ACN). How to prepare such a mobile phase?
Thank you.

Ps: I don't speak English well yet, sorry for the spelling mistakes

Hello,

I have a question about the preparation of the mobile phase.
In all the articles that I have read the proportion of solvent in the mobile phase is always 100% for example 70/30 (ACN / MeOH) so for a liter 700 ml of ACN + 300 ml of MeOH are mixed to obtain the mobile phase.
Today I saw in an article that the mobile phase has a composition of 70/20/15 (MeOH / H2O / ACN). How to prepare such a mobile phase?
Thank you.

Ps: I don't speak English well yet, sorry for the spelling mistakes

If that is a correct composition then it would be listed at parts and not percentage. As you point out that would equal 105%, but if they measure the composition by weight them maybe they are using 70g+20g+15g for a total of 105g.

There is also the phenomenon where 100ml MeOH + 100ml H2O result in less than 200ml total because of the way the two mix(I believe something to do with hydrogen bonding and maybe bond angles). Some methods do correct for this and give strange mixture compositions as a result.

... but if they measure the composition by weight them maybe they are using 70g+20g+15g for a total of 105g.

doesn't necessarily need to be mass parts.
they could also be volume parts, 70 ml + 20 ml + 15 ml or a multiple of them.

As long as it's always prepared the same, the separation will be the same too (assuming the lab is more or less air conditioned) and the total volume doesn't matter at all.

Mobile phases in thin layer chromatography are usually given in this format, but indicated as (V/V/V) to point out as volume parts.

But things like that, tells us to write down essential parts of a method as clear and unambiguously as possible.

Yes, it is a source of great irritation that if you take a particular buffer or solvent specification and give it to 10 analysts who've never met one another, the chances are you'll get at least 8 different interpretations (of which 6 are really quite sensible, and only one - mine! - is correct).
Mixtures of solvents can be exothermic or endothermic. Mixtures of analysts, under these circumstances, are generally exothermic. But as the previous poster said, if you do the same thing every time, the separation will be the same. It's jolly nice if when you publish, the editor actually lets you describe what you did in sufficient detail that it can be reproduced, rather than wibbling about word-counts.

Yes, it is a source of great irritation that if you take a particular buffer or solvent specification and give it to 10 analysts who've never met one another, the chances are you'll get at least 8 different interpretations (of which 6 are really quite sensible, and only one - mine! - is correct).
Mixtures of solvents can be exothermic or endothermic. Mixtures of analysts, under these circumstances, are generally exothermic. But as the previous poster said, if you do the same thing every time, the separation will be the same. It's jolly nice if when you publish, the editor actually lets you describe what you did in sufficient detail that it can be reproduced, rather than wibbling about word-counts.

Very true. I read a short paper last week about how a new column phase gave such great separation of difficult to separate analytes and showed a few nice chromatograms but failed to list the mobile phase used anywhere in the paper. Kinda difficult to duplicate and use the new column if you don't know what mobile phase to use.