Separation of ions that spontaneously convert to each other

Discussions about IC and related topics

6 posts Page 1 of 1
Is an ionic chromatograph able to separate ionic species that are in equilibrium with each other?
What exactly happens when an ion that is in equilibrium with other ionic species (e.g. hydrogen phosphate with dihydrogen phosphate, chromate with dichromate) moves through a separation column?
Dear Telesforo Bruni

It is not possible to separate e.g. hydrogen phosphate and dihydrogen phosphate or similar.
These ionic forms depend on the pH of the solution. When the sample is injected to the eluent, the eluent's pH defines the ratio of the two species. Elution takes place according to the "charge" of the ion (i.e. 1.5 if the ratio is 1:1).
Dr. Markus Laeubli
Manager Marketing Support IC
Metrohm AG
9101 Herisau
Thus the same ion while it is in one form runs through the column at a certain speed, while it is in the other form at another speed, but the result at the end is that all the species in equilibrium with each other come out at the same time and produce only a single peak.
The rate of the ion mixture is given by the mean, weighed on the concentrations at the pH of the eluent, of the rates at which the individual ionic forms flow.
If the ion is in equilibrium with a non-ionic form (e.g. completely protonated acid), then this molecule has the same velocity as the eluent, being without charge.

Is that right?
To phrase it in a slightly different way: in effect, a compound at its own pKa spends half the time ionized and half the time neutral, but because the rate of interconversion is orders of magnitude faster than the rate of migration through the column, it behaves as though it has a fractional charge.
-- Tom Jupille
LC Resources / Separation Science Associates
+ 1 (925) 297-5374
You can't separate e.g. hydrogen phosphate and dihydrogen phosphate or similar.
geometry dash free online
Super interesting, I'm definitely learning a lot here. area rug cleaning
6 posts Page 1 of 1

Who is online

In total there are 0 users online :: 0 registered, 0 hidden and 0 guests (based on users active over the past 5 minutes)
Most users ever online was 599 on Tue Sep 18, 2018 9:27 am

Users browsing this forum: No registered users and 0 guests

Latest Blog Posts from Separation Science

Separation Science offers free learning from the experts covering methods, applications, webinars, eSeminars, videos, tutorials for users of liquid chromatography, gas chromatography, mass spectrometry, sample preparation and related analytical techniques.

Subscribe to our eNewsletter with daily, weekly or monthly updates: Food, Environmental, (Bio)Pharmaceutical, Bioclinical, Liquid Chromatography, Gas Chromatography and Mass Spectrometry.

Liquid Chromatography

Gas Chromatography

Mass Spectrometry