Establishment and Validation of Sandell-Kolthoff Method for Saliva Iodine Determination

Saliva iodine is a useful biochemical marker for evaluating iodine status and controlling iodine-related diseases. This study aims to establish and validate a simple, reliable, and low-cost Sandell-Kolthoff (S-K) method for the determination of iodine in saliva. The method was established by considering the digestion solution type, concentration, dosage, digestion time and temperature, the volume of saliva samples, glass tube size, dosage of arsenious acid solution and ammonium ceric sulfate solution, and warm bath time. Then, the effectiveness of the method was examined by the linearity of the standard curve, detection limit, precision, and accuracy. The 1.5 mL 1 Mol/L ammonium persulfate solution at 100 °C for 90 min, the 200 μL saliva sample, glass tubes of 15 mm × 120 mm, 2.5 mL arsenious acid solution, 0.3 mL ammonium ceric sulfate solution, and 15 min for warm bath was selected to determine saliva iodine. In terms of validation of the S-K method, the linearity method has the linear range of the standard curve from 0 to 300 μg/L and the coefficient of determination ≥ 0.999; the detection limit, when the volume of saliva samples was 0.2 mL, was 4.6 μg/L; for precision, the relative standard deviation was from 0.3 to 2.8%; and for accuracy, the total recovery rate ranged from 92.8 to 107.0%. This S-K method is easy to operate, has good precision and accuracy, and can be used as a method to determine saliva iodine. It has great potential practical value in disease prevention, clinical auxiliary diagnosis, and experimental research.