Method with low usage amount of arsenic trioxide for measuring high concentration iodine in urine by As3+-Ce4+ catalytic spectrophotometry using ammonium persulfate digestion

Objective To establish a new method with low usage amount of arsenic trioxide for measuring 300 - 1200 μg/L high concentration iodine in urine by As3+-Ce4+ catalytic spectrophotometry using ammonium persulfate digestion, which would be convenient for monitoring urinary iodine in excessive iodine regions and to reduce environmental arsenic pollution. Methods Calibrators and urine samples(0.20 ml each) were digested according to the current standard detection method of urinary iodine(WS/T 107-2006). At the same time, improving the current standard method, the amount of arsenious acid solution was reduced from 0.100 moL/L H3AsO3 (containing NaCl 25 g/L) 2.5 ml to 0.025 mol/L H3AsO3(containing NaCl 40 g/L) 2.5 ml; amount of ceric ammonium sulfate solution was reduced from 0.076 mol/L 0.30 ml to 0.025 mol/L 0.50 ml; and photometric wavelength was changed from 420 nm to 380 nm. The new method was evaluated by standard curve linearity and linear range, sample detection precision, accuracy, and the results of urinary iodine were compared with those determined bycurrent standard method, and this new method was also tested of suitable combination of reaction temperature and reaction time of cerium arsenic in the temperature range of 20 - 30 ℃. Results The calibration relation of C =a + blgA (C: iodine concentration, A : measuring absorhance) in the new method existed when As3+- Ce4+ catalytic reaction was kept at a certain stable temperature range between 20 - 30 ℃ and in certain fixed reacting time. The linear range of the calibration curve was 300 - 1200 μg/L and the linear correlative coefficient was- 0.9999. The relative standard deviations(RSD) were 1.0％(3.2/330.3), 0.4％(2.0/517.3), 0.5％(3.9/712.6) and 0.9％(9.4/1042.3) when measuring urine samples with iodine concentration of 330.3, 517.3,712.6, and 1042.3 μg/L, respectively. The total average recovery was 98.3％ with a range of 93.4％ (186.8/200.0) - 101.5％ (202.9/200.0) when measuring 4 urine samples containing different concentration of high iodine, and average recovery was 99.1％ (148.6/150.0), 97.5％ (195.0/200.0), 98.8％ (395.3/400.0), and 98.2％ (392.7/400.0),respectively. The test results of four urinary iodine standard materials were all within the given value range and the relative deviations(RD) were all ＜ 2.0％ at different test temperature, respectively. No significant difference was found between the results of the 16 urine samples containing high concentration of iodine determined by the new method and the current standard method (|t| =0.727, P ＞ 0.05). The table of suitable combination of As3+-Ce4+ reaction temperature and reaction time for this method was obtained(such as 20 ℃ and 33 min, 25 ℃ and 25 min,30 ℃ and 19 min, etc). Conclusions This method greatly reduces the amount of arsenic in waste, reduces pollution, saves reagents, and this method is easier to be performed with better precision and accuracy, which is suitable for measuring high concentration of iodine in urine. Key words: Iodine; Urine; Spectrophotometry; Arsenic