A study on the reagent condition for measuring iodine in serum by direct dilution sampling-inductively coupled plasma mass spectrometry

Objective To screen a suitable reagent system for measuring iodine in serum by direct dilution sampling-inductively coupled plasma mass spectrometry (ICP-MS). Methods Experiments were on sample dilution method for standard solutions and serum samples with six different diluents. After dilution, the concentration of iodine in serum was determined by ICP-MS method. The rhenium (Re) and tellurium (Te) was used as internal standard element, respectively. The effects of the two internal standard elements on determination results were compared. And the results were compared with the results determined by the current serum iodine arsenic cerium catalytic spectrophotometry standard method (WS/T 572-2017), hereinafter referred to as the standard method. The methodological evaluation of this new method was done through standard curve linearity, sample detection limit, precision and accuracy in determining serum iodine in the range of 0-300 μg/L. Results The direct dilution sampling-ICP-MS method screened for measuring iodine in serum was preparing 1 L of 2.0 g/L ascorbic acid, 1.0 g/L ammonium chloride, 0.10% ethanolamine, and 1.0% ethanol as diluent; the standard solutions and the serum samples were all diluted in a ratio of 1∶19 (sample ∶ diluent) before testing with Re as internal standard element. The linear range of the calibration curve was 0-300 μg/L and the linear correlative coefficient was 0.999 9. The detection limit for serum iodine was 1.2 μg/L (0.20 ml of serum was tested). Precision: the range of the intra assay coefficient of variation (CV) was 0.2%-1.2% (n=6) and the range of the inter assay CV was 0.4%-1.9% (n=3) when measuring 5 serum samples. Accuracy: The average recovery was 97.9% with a range of 93.9%-103.8% when measuring 8 serum samples. No significant difference was found between the results of the 35 serum samples determined by the standard method and the new method (t=0.178, P > 0.05). Conclusions Re performs better than Te in determination of iodine as an internal standard element. The reagent system screened for determination of iodine in serum does not require matrix matching. This method has good standard curve linearity, high sensitivity, good precision, accuracy and anti-interference ability, and is easy to be used and quickly to be analyzed of the test results, which is suitable for widely application in determining serum iodine. Key words: Iodine; Serum; Inductively coupled plasma mass spectrometry; Diluent