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Semantics: Eluents-Solvents-Mobile Phase
Posted: Fri Mar 21, 2008 7:26 pm
by rhaefe
What is the proper way to name the different components of the actual mobile phase?
Lets say I have 100% water in channel A and 100% acetonitrile in channel B but do an isocratic separation of 50%A and 50% B. So, my actual mobile phase is 50% acetonitrile. Do you refer to the solvents in channel A and B as:
(1) Mobile phase A and mobile phase B
(2) Eluent A and eluent B
(3) Solvent A and solvent B
(4)????
I know it is splitting hair...
Posted: Fri Mar 21, 2008 8:04 pm
by DR
I would indicate the contents of the final mixture and specify that it was mixed by the LC pumps.
That way, others will quickly be able to tell you why you had problems with outgassing, temperature and pressure related retention time stability issues, and baseline noise due to refractive index variations.
(in other words, premix your mobile phase, degas it and call it 50% ACN in water
)
Posted: Fri Mar 21, 2008 9:18 pm
by rhaefe
DR,
thanks, but I was probably not clear. I understand your suggestion and agree with it. I am still wondering what the solvents in channel A and B are referred to as (lets say when I run a gradient). Mobile phase A and B are in my opinion incorrect since because according to IUPAC:
mobile phase (in chromatography)
A fluid which percolates through or along the stationary bed, in a definite
direction. It may be a liquid (liquid chromatography) or a gas (gas chromatography)
or a supercritical fluid (supercritical-fluid chromatography).
In gas chromatography the expression carrier gas may be used for the
mobile phase. In elution chromatography the expression ‘eluent’ is also
used for the mobile phase.
1993, 65, 824; 1990, 62, 2202; O.B. 97
IUPAC
That leaves solvent A and solvent B or eluent but in the IUPAC definition, this can also be the mobile phase...
It is purely a semantics issue I guess.
Posted: Tue Mar 25, 2008 2:41 am
by tom jupille
It is purely a semantics issue I guess.
Umberto Eco, in his novel Foucault's Pendulum, described Tetrapyloctomy: the art of splitting hairs . . .
. . . four ways.
It's usually clear from context, but if you define the mobile phase as what comes out of the pump / into the column, then what goes into the pump would be distinguished as "solvent A", "solvent B", . . . etc.
Posted: Tue Mar 25, 2008 11:32 am
by Peter Apps
How about mobile phase component A and component B. ?
Until one of them is a buffer, with three components !
Peter
Posted: Tue Mar 25, 2008 4:55 pm
by DR
The only distinction I can see that may be worth drawing is between solvent and eluent.
If you're doing preparative chromatography and have a bunch of some fairly non-polar molecule in a pretty large volume of water (your solvent), and you loaded it onto a prep column, you would eventually want to switch to something less polar to elute your stuff from the column (your eluent).
Beyond that, I really don't think it matters much and use of mobile phase A, B... is pretty universally understood with respect to analytical liquid chromatography.
:: adds Foucault's Pendulum to the "to do" list ::