Double-wavelength spectrophotometric determination of iodine in salt with I(V)-iodide-safranine T system.

A new method for determination of iodine was developed by double-wavelength spectrophotometry using 360 nm as the measurement wavelength and 513 nm as the reference wavelength.The method is based on the reaction of I(V) with excess I-in 0.2 mol/L H3PO4 to produce I3-,and it further reacts with safranine T(ST) to form a stable ion-association complex(2∶1),which exhibiting a positive absorption peak at 360 nm and a negative absorption peak at 513 nm.Beer's law was obeyed for 0~0.7 μg/mL I(V).The apparent molar absorptivity was 1.27×105 L·mol-1·cm-1,and the limit of detection was 11.9 μg/L.The method was applied to determine iodine in low sodium salt and salt fortified with zinc.The results showed good agreement with those obtained by iodimetry.RSD was less than 1.54 %(n = 5).Recovery varied from 98.4 % to 99.1 %.