Determination of sodium isethionate

Unreacted sodium isethionate is the only other impurity likely to be present in significant amounts. It is determined by determining total anions by ion-exchange conversion to the corresponding acids and titration with alkali, then determining the active, soap and chloride contents and finding the isethionate by difference. 

Prepare an ion-exchange column containing 40 meq of a strongly acidic cation exchanger hydroxide in 80% methanol. 

Dissolve a sample containing about 5 g active in 50 ml 80% methanol and neutralise to phenolphthalein with methanolic sodium hydroxide. 

Transfer the solution to the column and allow it to flow through, collecting the effluent in a 500 ml volumetric flask. Wash with five bed-volumes of water, collecting the effluent in the same flask. Dilute to volume and mix. 

Wash the column with a further three bed-volumes of water. 

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