Method with low amount usage of arsenic trioxide for measuring iodine in urine by As (Ⅲ)-Ce4+ catalytic spectrophotometry using ammonium persulfate digestion / 中国地方病学杂志

ABSTRACT

Objective To improve the current standard method of measuring urinary iodine by As (Ⅲ)-Ce4+catalytic spectrophotometry, reducing the amount of arsenic toxic reagent used to decrease environmental pollution,and make the modified method with good precision and accuracy. Methods For improving the current standard method of measuring urinary iodine, amount of arsenious acid solution was reduced from 0.100 mol/L H3AsO3(which contains NaCl 25 g/L) 2.5 ml to 0.025 mol/L H3AsO3(which contains 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 0.30 ml;photometric wavelength was changed from 420 nm to 400 nm. The new modified method was evaluated by standard curve linearity and linear range, sample detection limit, precision, accuracy, and urinary iodine values, and the rates of absorbance change in the test process were compared with the current standard method. Results The calibration relation of C= a + blgA (C iodine concentration, A measuring absorbance) in the new modified method existed when As3+-Ce4+ catalytic reaction was kept at a certain stable temperature range between 20 - 35 ℃ and in certain stable reacting time. The linear range of the calibration curve was 0 - 300 μg/L and the linear correlative coefficient was - 0.9998. The detection limit for iodine was 4 μg/L(0.25 ml of urine was tested). The test coefficient of variations(CV) were 1.7%(1.1/66.0), 1.8%(1.4/76.0), 2.0%(3.0/147.5), 1.6%(4.2/265.5) when measuring urine samples with iodine concentration of 66.0, 76.0, 147.5, 265.5 μg/L, respectively. The average recovery was 100.6% with a range of 95.0% (57.0/60.0) - 103.7% (62.2/60.0) when measuring 4 urine samples containing different iodine concentration, and average recovery was 101.0% (40.4/40.0), 100.4% (100.4/I00.0), 100.5% (60.3/60.0),100.4% (100.4/100.0), respectively. The test results of two national standard urinary iodine were all within the given value range and the relative deviation(RD) was 0.05). The table of suitable combination of As3+-Ce4+ reaction temperature and time for this method was obtained(such as 20 ℃ and 53 min, 25 ℃ and 40 min, 30 ℃and 30 min, etc. ). Compared with the standard method, the rates of absorbanee change of As ( Ⅲ )-Ce4+ reaction in the new modified method were more slowly, which further reducing the determination deviation caused by the temperature fluctuations or measuring time deviation in measurement process. Conclusions This new modified method greatly reduces the amount of arsenic in waste, reduces pollution, saving reagents, and this method is easier to operate with better precision and accuracy, which is suitable for application of measuring iodine in urine.