Determination of urine iodine by the arsenic cerium catalytic rate method

Objective To establish a arsenic cerium catalytic rate method for determination of urinary iodine, and increase the linear range of urinary iodine determination. Methods Standard series and urine samples after digestion treatment, were tested using dynamics function of spectrophotometer to record the curve of absorbance value (A) change with time (t) during arsenic cerium catalytic reaction for each measurement system, choice (A1, t1) and (A2, t2) on this curve and calculating the reaction rate (v), v= (lgA1-lgA2)/(t2-t1). Through the determination of the standard series it could calculate regression equation of iodine concentration (C) with X: C= a+ bX, X= 1 000 (v-v0), and the v0 is the reaction rate of reagent blank. Results ①C and X were positively correlated. The standard series linear range was 0-1 200 μg/L and correlation coefficient r was higher than 0.999 1. The minimum detection limit was 3.9 μg/L (0.25 ml urine). ②Precision: 5 urine samples (A, B, C, D, E) were selected within the range of 0-1 200 μg/L and the measured value were (72.3 ± 2.7), (148.2 ± 5.2), (210.5 ± 4.4), (562.7 ± 6.8), and (899.3 ± 8.0) μg/L. The relative standard deviation (RSD) was between 0.9%-3.8%. ③Accuracy: 4 samples (A, B, C, D) were measured for standard addition recovery test, recovery was between 94.2%-107.2%; urinary iodine standard material [the given values were (67.9 ± 9.0), (142.0 ± 10.0), (195.0 ± 10.0), (558.0 ± 17.0), (885.0 ± 28.0) μg/L] were determined and the results were in the range of uncertainty of the standard material. ④Method contrast: with the national health standard method (method for determination of iodine in urine by arsenic cerium catalytic spectrophotometry) to determinate 120 urine samples, the results showed that there were 60 urine samples within 0-300 μg/L, 60 urine samples were more than 300 μg/L. Then rate method was used to test the 120 urine samples. For the 60 samples within the scope of 0-300 μg/L, the determination results of the two methods were positively correlated (r= 0.994, P 0.05). Conclusions Arsenic cerium catalytic rate method has increased the linear range of urinary iodine determination. Using this method, the vast majority samples can be tested directly without dilution, thereby reducing the workload for determination of urine iodine. Key words: Urine; Iodine; Rate method; Arsenic cerium catalytic reaction