Standards for standardization of reducing agents: K2Cr2O7 KIO3 Ce4+ Standards for standardization of oxidizing agents: Na2C2O4 Na2S2O3 Fe2+ (Mohr’s salt and Oesper’s salt) 4 .V. Auxiliary Oxidizing and Reducing Agents The analyte must be in a single oxidation state at the start of the titration. This can be achieved by using a preoxidation or pre-reduction step prior to analysis