Study On The Determination And Analysis Method Of Microamounts Of Iodine Content In Biological Materials

Iodine is one of essential micronutrients in the human body, which can maintain basic life activities and the physiological functions of the pituitary gland and promote the physical and brain development. Long-term insufficient iodine intake, such as endemic goiter and endemic cretinism, can cause iodine deficiency disorders. Analysis of iodine content in different biological samples and the Chinese people'food in particular and speculation of the iodine intake of the body from food can provide some guidance for determining the significance of reasonable iodine need for human health. Iodine is one of the elements difficult to detect because of its unstable chemical characteristics. Iodine in biological materials has its low content, complex basic ingredients, large individual differences and interfering with many components. Therefore, it is of great significance to develop a highly accurate, stable, rapid and sensitive method for trace iodine determination. At present, microamount of iodine is commonly detected by manual method, by which the reaction temperature and reaction time are difficult to be controlled strictly. Thus, this method can lead to unstable measurement results. Besides, various interference factors in experimental process and iodine pollution are important reasons for poor accuracy. In the present study, we aimed to investigate and establish the instrumental analyzing method of the sequential injection catalytic spectrophotometric determination of microamount of iodine, to eliminate the artificial limitations of manual detection and to detect iodine content in biological samples from different sources, which can provide a scientific basis for the adjustment of iodized salt concentration and monitoring of iodine nutrition.In the present study, the analyzing instrument for microamounts of iodine determination was designed on basis of sequential injection solution delivery principle and by using the programmable syringe pump to push carrier liquid and reagents. The self-designed 16-hole program-controlled selection valve was used to achieve automation of sequential injections of the samples, mobile delivery, residence stabliztion and residence testing. The sequential injection detection of microamounts of iodine was established which was characterized by stable determination condition, rapid analysis, broad linear range, high sensitivity, automatic detection, accurate and rapid detection of iodine in biological samples, and had good application prospects. This method had its linear range of 15~600μg/L, the detection limit of 5.01μg/L (n=11), recovery of 94.1%~105.1% and the determination results of the national standard reference material (GBW09109 and GBW09110) in a given standard value range. The detection of iodine content in biological samples from different sources showed that the iodine contents of 25 types of food (from Harbin) samples (Meat, eggs, grain, vegetables, fruits, etc.) varied from 10μg/kg to 2000μg/kg, with a highest iodine content of 2424.2μg/kg in fresh Kelp, higher iodine content in meat and eggs than grain, a low iodine content in fruits and vegetables. According to the detection results and people's daily intake from various food, we determined that total daily intake of iodine of the urban population in Harbin was slightly higher than the recommended amounts of the normal population (150μg/d). The iodine intake from salt (35±15 mg/kg) was greater than from other types of food, therefore, reducing the intake of iodized salt, or declining the iodine content of iodized salt by government appropriately based on actual situation were proposed and contributed to keep iodine intake normal.The urine, salt samples of several women of childbearing,pregnant women and school-age children were determined and the result showed that urine iodine range was 70-370μg/L.The urine iodine values of women of childbearing group and pregnant woman group as well as pregnant women and school-age children were statistically analyzed and the result showed there were significant differences between both groups and the urine iodine of pregnant women and childbearing women were lower than that of school-age children. The investigation showed that there were still some problems with the iodine nutrition status of some pregnant women. Given the special physiological characteristics of pregnant women, the odine nutrition surveillance and health care of this part of the population should be strengthened. The urine content of salt was 31.2 mg/kg.The urine content of drinking water was 5.6μg/L.The biological iodine in the seaweed was dected by our instrument and method. The dissolution of iodine in the seaweed at different soaking conditions was studied. We found that during kelp soaking, the amount of soaked iodine was associated with soaking time, the volume of soaking water, soaking temperature and the pH value of soaking solution, and the effect of the soaking time and soaking temperature on the amount of soaked iodine were most remarkable.The seaweed iodine can be recommended as an active biological iodine source.The use of seaweed iodine in the soil amplifies the iodine content of the environment, which increases the feasibility of bio-geochemical study on iodine in the environment, elevates the iodine in the crop, and contributes to explore a more efficient and safe way of iodine supplement for human bodies.