Can someone explain in lay man terms what is difference between free base and salt form reference standards?
This is a simple phenomenon.
For example, The API / drug compounds such as Chlorpheniramine maleate, Ephedrine hydrochloride, Codeine phosphate, Dextromethorphan hydrobromide, Salbutamol sulphate are the salts of bases (main API molecules), and acids such as Maleic acid, Hydrochloric acid, Phosphoric acid, Hydrobromic acid, and Sulphuric acid respectively.
These API salts are soluble in aqueous media and water.
In the aqueous solutions of these salts, they undergo dissociation into free bases and acid radicles. The free bases are positively charged ions while acid radicles are negatively charged ions.
Salbutamol Sulphate + Water (H2O) = Salbutamol (++) and SO4 (- - )
H2O = 2H (+) & O (- -)
Salbutamol 2(H +) is called “Protonated” in its aqueous solution.
The basic API molecules are Chlorpheniramine, Ephedrine, Codeine, Dextromethorphan, Salbutamol. These are called “Free bases”. Generally, bases of APIs are insoluble or sparingly soluble in water or aqueous medium and these are unstable. While salts of APIs are freely or highly soluble in water (with some exceptions) and are more stable than their bases.
Hope I have clarified the matter.