Method for balancing background conductivity for ion chromatography

DETAILED DESCRIPTION In accordance with the invention, a method has been provided for balancing the background conductivity in an ion chromatography system using a gradient eluent with a progressively increasing concentration of electrolyte.
It is particularly useful when the system includes a suppressor of the membrane type.
In this system, a non-ionic counterbalancing precursor, preferably a polyhydroxy compound, e.
g.
, mannitol, is pumped with the gradient eluent.
As the electrolyte concentration increases during a run, the precursor concentration correspondingly decreases.
Since the precursor is non-ionic, it does not affect separation of the ions in the chromatographic column.
The effluent from the chromatographic column is flowed through a conductivity detector for detection of the separated anions.
Prior to passage into the conductivity detector, a complexing agent, preferably boric acid, is added to the effluent.
Such complexing agent is of a type which reacts with the counterbalancing precursor to form a highly ionized complex at an ion concentration counterbalancing the increasing background concentration of the electrolyte flowing through the conductivity detector during the run to stabilize the level of background ion concentration.
If a membrane suppressor is used, the complexing agent is of a type which passes through the membrane.
For this purpose, assuming the complexing agent to be an acid, it is preferable that it be non-ionic or weakly ionized so that it may pass through a cation membrane which is used in the detection of anions.
One advantage of the above system is that the same gradient pump for the gradient electrolyte also is used for the counterbalancing precursor.
Also, the pump for the regenerant, typically of a non-gradient type can also be used for the complexing agent since it may be supplied at a constant concentration.