An ion exchange process to convert chloride intermediate to acetate API was developed and successfully scaled-up using Process Analytical Technology (PAT). Chloride ion breakthrough curves were measured with the on-line PAT, and supplemented with HPLC data on product stream impurities. The measurements lead to the relative dynamic binding capacity of the resin. The adsorption isotherm and static binding capacity of the ion exchange resin were measured and used in simulations showing the elution of competitive species in the system. This more fundamental approach to ion exchange development allowed the column design and operation to go beyond exchanging chloride anion with acetate, to also purifying the product.