Protocol for the Determination of Total Iodine in Iodized Table Salts Using Ultra-High-Performance Liquid Chromatography

Potassium iodate and potassium iodide are commonly fortified in iodized table salt, which must be continuously monitored to maintain quality. Our study reported an optimized detection method for total iodine in iodized table salt using 0.5 M sodium bisulfite as the reducing agent. The iodized table salt (0.5 g) was dissolved in 0.5 M sodium bisulfite solution prior to injection in ultra-high-performance liquid chromatography (UHPLC) coupled with a diode array detector using a weak anion-exchange column (2.1 mm × 150 mm, 5 μm). Iodide was eluted at 9.92 ± 0.06 min (λ = 223 nm) when an isocratic mobile phase of 1:1 (v/v) methanol/120 mM phosphate buffer mixed with tetrasodium pyrophosphate (pH 3.0) was running at 0.20 mL/min (15 min). Iodide was detected as total iodine from 10.0 to 50.0 mg/kg with a limit of detection (LOD) of 1.2 mg/kg and a limit of quantification (LOQ) of 3.7 mg/kg. The method was validated with relative standard deviations (RSDs) of 4.2%, 0.4%, 1.6%, and 0.8% for accuracy, repeatability, intermediate precision, and robustness, respectively. The determination of total iodine was successful on six (6) samples (n = 3), which recovered 87.2–106.9% of iodate and iodide spike. Thus, this study provides a validated protocol for the determination of total iodine in iodized table salt using 0.5 M sodium bisulfite.