Online monitoring of the salt chemistry in working MSRs is imperative for the safe and efficient operation of these reactors for a number of reasons. First, molten alkali halides become corrosive in the presence of impurities. Second, in the presence of corrosion and fission products, the salts might change their thermophysical and thermochemical properties, leading to stress-corrosion cracking , undesired plating on metal parts , or changes in the salt ther-mophysical properties. To mitigate changes in the salt during operation, the redox potential of the salt should be monitored and controlled . Moreover, detailed information on the concentration of corrosion and fission products is necessary to understand and mitigate effects of impurities and to measure the efficacy of salt cleaning procedures.