Achieving the 'Holy Grail' of anion chromatography by developing a suppressor which can remove carbonate
The new dual suppressor allows Metrohm to perform IC gradients, which so far has not been a feature within the Metrohm range. Rather than copy existing technology, Metrohm has kept to its original innovative philosophy and generated its own novel ideas on how IC should be developed.
To date, all anion chromatography performed with gradients is completed almost exclusively with alkali eluents.
The problem with alkali (OH) eluent is that it is a weak eluent.
So quite strong concentrations of alkali are required to shift late eluting ions off the column.
This is a small cost as ion chromatographers are happy to work with alkali. When alkali (OH) is chemically suppressed, it is converted from hydroxide to water, giving a zero conductivity baseline.
Even with a gradient, the baseline is flat.
However, it has some practical difficulties.
The hydroxide eluent is not very stable. It absorbs CO2 very readily, causing shifting in the retention times.
The chromatography is prone to carbonate and system peaks, affecting the quality of the chromatography and the integrity of the results generated.
It has been known for a long time that the use of a bicarbonate / carbonate eluent would be a technical advantage over hydroxide eluent.
They are easy to prepare and very stable.
No expensive eluent generation modules and consumables would be required.
More importantly, the chromatography, bicarbonate/carbonate eluents are stronger eluents than alkali eluents.
This allows shorted run times and faster column recovery from a gradient use.
Unfortunately, when carbonate and bicarbonate eluents are chemically suppressed, they are converted to the carbonic acid.
Carbonic acid is not fully suppressed as it is only partially dissociated.
So when used in a gradient system, the baseline conductivity is not flat. Chromatographers prefer to operate under flat stable baselines. It has long been the 'Holy Grail' of anion chromatography to develop a suppressor which could remove carbonate.
The unique Metrohm new dual suppressor chemically suppresses carbonate and removes the carbonic acid.
It is really a two-stage process.
Hence the name dual suppressor.
There are many benefits.
You buy two suppressors in one and yet you get three (a chemical suppressor, a carbonate suppressor, and an electronic suppressor).
The main advantages over alkali eluents are: no water dip using a carbonate eluent; no system peak using the carbonate eluent; gradient with carbonate eluent; stable eluent, reproducible baselines; shorter chromatography run times as bicarbonate and carbonate are stronger eluents; shorter recovery times after a gradient has completed; no solutions are required for the suppressor.
It is an electronic suppressor and so continuous.
