Simple electrochemical method for the quantification of chlorite in aqueous and non-aqueous media

Abstract

The recent recommendation of the WHO for a limit of chlorite of 0.7 mg L−1 calls for reliable and fast analysis methods. Here, we present a robust differential pulse voltammetry (DPV) method for the quantification of chlorite (ClO2−) well below this limit. Different working electrode materials and electrolytes were evaluated, of which the combination of glassy carbon with bis(trifluoromethylsulfonyl)azanide (NTf2−) salts turned out to be highly advantageous. It was found that for aqueous samples the lithium salt of NTf2− was most suitable, while for organic systems solutions of the ionic liquid N‑butyl‑N-methylpyrrolidinium bis(trifluoromethylsulfonyl)azanide ([BmPyrr][NTf2]) in methanol were the most robust ones. Neither the other chlorooxo anions (hypochlorite OCl−, chlorate ClO3−, perchlorate ClO4−) nor the standard ions, except iodide, interfere with the method. To demonstrate the feasibility of the method, a broad range of samples were investigated for their chlorite content, such as commercial disinfectants, bleaches, chlorinating agents, organic acid chlorides, as well as products of the Pinnick reaction, for which chlorite is used as a reagent.