A method for determination of urinary iodine by inductively coupled plasma mass spectrometry with no need for base urine match

Objective To establish a method for determination of iodine in urine with no need for base urine match by inductively coupled plasma mass spectrometry (ICP-MS). Methods The diluent which contains 2.5 g/L N2H4·2HCl-1.0 g/L NH4Cl-0.50%HCl-2.0%C2H5OH were used to eliminate the matrix interference in determination of iodine in urine by ICP-MS. The standard solutions and the urine samples were all diluted in a ratio of 19 ∶ 1 (diluents ∶ sample) before testing. The methodological evaluation of this new method was done through standard curve linearity, sample detection limit, precision and accuracy in determining urinary iodine. And the determine results were compared with the current urinary iodine arsenic cerium catalytic spectrophotometry standard method (WS/T 107.1-2016, hereinafter referred to as the standard method). Results The linear range of the calibration curve was 0- 1 000 μg/L and the linear correlative coefficient was 0.999 9. The detection limit for urinary iodine was 0.4 μg/L(0.25 ml of urine was tested). Precision: The average coefficient of variation (CV) was 0.8% with a range of 0.2%- 1.7% (n= 6) when measuring 33 urine samples with iodine concentration of 26.5- 854.4 μg/L. Accuracy: The iodine standard of 40- 400 μg/L was added for recovery test. The average recovery was 99.6% with a range of 94.3%- 103.4% when measuring 24 urine samples with iodine concentration of 26.5- 858.3 μg/L. The test results of 8 urinary iodine national standard materials with iodine concentration ranged from 64.5 to 883.0 μg/L were all within the given value range and the relative deviations were all below 3.0%(n= 12). No significant difference was found between the results of the 51 urine samples determined by the standard method(WS/T 107.1-2016) and the new method (t= 0.836, P>0.05). Conclusions The new method to determine iodine in urine with no need for base urine match is successful established. This method has wide linear range, high sensitivity, good precision, accuracy and anti-interference ability, and is easy to be used and quickly to be analyzed of the test results, and is suitable for widely application in determining urinary iodine. Key words: Iodine; Urine; Inductively coupled plasma mass spectrometry; Diluent