Objective To establish a fully automated online digestion colorimetric method for the determination of iodine in urine, and to evaluate its performance.

Methods Based on the health industry standard arsenic-cerium catalytic spectrophotometric method, urinary iodine was determined using a fully automated online digestion iodine analyzer, which automatically performed sample aspiration, reagent addition, digestion, incubation, and colorimetric measurement. The measurement range, precision, accuracy, and performance in actual urine samples were experimentally evaluated.

Results The linear ranges of the method were 0-300 μg/L and 300-1 200 μg/L, with correlation coefficients greater than 0.999. The limit of detection was 1.245 μg/L. The RSD ranged from 0.29% to 3.08%. The spiked recoveries of urine samples were 95.50%-108.92%. The results for reference materials were all within the certified reference ranges, with relative errors of -4.67% to 2.52%. The urinary iodine results obtained with the fully automated iodine analyzer were generally consistent with those obtained by the health industry standard method. For both low- and high-concentration quality control samples and actual urine samples, accurate determination of urinary iodine samples at concentrations ≤1 200 μg/L could be achieved by four-fold dilution with purified water followed by the low-range method, 0-300 μg/L. The precision and accuracy met the technical requirements for urinary iodine testing.

Conclusion The fully automated online digestion colorimetric method established in this study enables complete process automation for urinary iodine determination. It is safe, environmentally friendly, efficient, sensitive, accurate, and labor-saving, and can provide strong technical support for iodine nutrition monitoring and large-scale screening in primary-level laboratories.