Fading spectrophotometric determination of iodine in phosphate rock with I(V)-iodide-acridine orange complex system

A new fading spectrophotometric method for determination of trace iodine was developed.I(V) reacts with excess I-in 0.048 mol/L H3PO4 to produce I3-.After adding NaAc,I3-,further reacts with acridine orange(AO) to form an ion-association complex(1∶1),leading to the fading of AO.Beer's law for 0-0.48 μg/mL I(V) with the maximum fading wavelength locating at 491 nm in the visible region.The apparent molar absorption coefficient(e) was 1.72×105 L·mol-1·cm-1 and the detection limit was 7.47 μg/L.The interferences of oxidants including MnO4-were eliminated by adding hydrazine hydrochloride.The interferences of metal ions such as,Ca2+ and Fe2+ were separated by cation exchange resin.The method was applied to determine iodine in phosphate ore samples.The results well agreed with those obtained using national standard method.RSDs of 5 determinations for iodine were less than 1.32 %,and recoveries after I(V) standard solution addition varied from 100.3 % to 101.0 %.