Iodine revisited: If and how inorganic iodine species can be measured reliably and what cause their conversions in water?

This study revisited a list of inorganic iodine species on their detections and conversions under different water conditions. Several surprising results were found, e.g., UV–vis spectrophotometry is the only reliable method for I 3 – and I 2 determinations with coexisting I – /IO 3 – /IO 4 – , while alkaline eluent of IC and LC columns can convert them into I – completely; IO 4 – can be converted into IO 3 – completely in IC columns and partly in LC columns; a small portion of IO 3 – was reduced to I – in LC columns. To avoid errors, a method for detecting multiple coexisting iodine species is suggested as follows: firstly, detecting I 3 – and I 2 via UV–vis spectrophotometry; then, analyzing IO 4 – (> 0.2 mg/L) through LC; and lastly, obtaining I – and IO 3 – concentrations by deducting I − and IO 3 – measured by IC from the signals derived from I 3 – /I 2 /IO 4 – . As for stability, I − or IO 3 – alone is stable, but mixing them up generates I 2 or H 2 OI + under acidic conditions. Although IO 4 – is stable within pH 4.0–8.0, it becomes H 5 IO 6 /H 3 IO 6 2 – in strongly acidic/alkaline solutions. Increasing pH accelerates the conversions of I 3 – and I 2 into I – under basic conditions, whereas dissolved oxygen and dosage exert little effect. Additionally, spiking ICl into water produces I 2 and IO 3 – rather than HIO.