We are using Sulfuric acid 1N in the solvent for a method on cation exchange column. The compound is Pseudoephedrine HCl. I could not find any reasonable explanation for that.

Thanks

I'm not quite sure if I understand the gist of your question by let me take a shot at it anyway:

Pseudoephedrine is a strongly basic compound amenable to cation exchange chromatography (it can also be analyzed by reversed phase chromatography but it is prone to poor peak shape on most reversed phase columns). The sulfuric acid is serving a function of providing an elution cation (i.e. hydronium ion) in order to accomplish the analysis. If your question is: why do I need to use such a concentrated eluent (or for that matter such an acidic eluent), the answer is undoubtedly connected to the use of a column with excessive cation exchange capacity coupled with a poor choice of elution cation. In reality, hydronium is the weakest elution strength cation. Better chromatography can be achieved using a significantly lower concentration of potassium chloride as the eluent (with a pH low enough to maintain ionization of the pseudoephedrine). Even better chromatography can be obtained using cesium chloride but that is somewhat expensive. Of course if the method you are using is a gel based resin, it must be packed in the salt form you intend the use so you can't simply switch to potassium form eluents without causing damage to your column. However, there are a number of low-moderate capacity Cation Exchange Columns suitable for this application which don't suffer from this problem. A good example is the OmniPac PCX-100 column from Dionex.

Pseudoephedrine can be separated without difficulties on most modern RP columns. No need to go through the ion chromatography complications!