Solid-Phase Extraction and Spectrophotometric Determination of Iodate in Table Salt after Azo Dye Formation

Abstract

Abstract A new reaction for determining iodate in table salt is proposed. It is based on oxidation of phenylhy-drazine-4-sulfonic acid by iodate in acidic medium to the 4-diazobenzenesulfonic acid cation and its electrophilic coupling with N-(1-naphthyl)ethylene- diamine dihydrochloride to give an azo dye, which is measured spectrophotometrically at 545 nm. Maximum molar absorptivity was 8.41 ×104 L/mol cm. A rectilinear calibration graph was obtained for iodate in the range 0.25–5 mg/L. The azo dye could be preconcentrated at least 40-fold by solid-phase extraction on C18 sorbent. The limit of detection was 0.6 μg iodate/L. The method was used to determine iodate in laboratory-prepared and commercially available table salt samples. Up to 5 mg bromate/kg and 10 mg iron(lll)/kg in table salt did not interfere.