Indirect Determination Of Iodine And Molybdenum By Atomic Fluorescence Spectrometry

Iodine and molybdenum are essential trace elements and directly or indirectly to involve in some vital activities in human body, therefore, they play an important role in the development and metabolism in our body. For any essential trace elements, if excess or shortage, there exists a risk of deteriorating our body. As a result, it becomes necessary to control or monitor these elements. Since we gain iodine and molybdenum mainly through the food intake, determination of these elements in food is significant, the obtained results provide a certain refernce to help us choose appropriate food. At present, there are many methods are used to measure iodine and molybdenum, however, this method in this thesis has not been reported.Because there are prominent advantages in determining arsenic and mercury by atomic fluorescence spectrometry (AFS), we can indirectly measure iodine or molybdenum when they form hydrophobic complex, which is extractable into an organic reagent, with either arsenic or mercury. Based on this idea, the samples are decomposed with microwave digestion, the target elements in the sample solution are complexed with either arsenic or mercury whoever could happen, then separated and enriched by solvent extraction, With the introduction of the solvent having the target element complex into an intermittent flow injection-hydride generation-atomic fluorescence spectrometer, indirectly determination of iodine or molybdenum is realized. In this experiment pure ethanol is used as a solvent to dissolve reducing agent or carrying flow solution for a complete mixing with the organic extrant. Under the optimized experimental and instrument conditions, this approach is applied to determine the iodine in eggs, molybdenum in tea and Chinese herbal medicine.A method has been developed for indirectly determination of iodine with methyl isobutyl ketone (MIBK) extraction by atomic fluorescence spectrometry (AFS). Based upon the complex, which can be extracted perfectly by MIBK, formed between I-and Hg2+in0.1mol·L-1of nitric acid, thus, indirectly measuring the iodine in organic phase becomes possible. The effects of extraction conditions and others influence factors are investigated. Under the optimized experimental conditions, the results show that the linearity between its fluorescence intensity and the concentration of iodine is0-12μg·L-1, and the relative standard deviation is3.3%, the detection limit is0.14μg·L-1, the method has been applied to the determination of iodine in eggs, the recoveries are in the range of101.8-110.4%.An analytical method for indirect determination of molybdenum in tea sample is established using atomic fluorescence spectrometry (AFS). Based upon the heteropoly arsenomolybdic acid, formed between As (V) and ammonium molybdate in0.3mol·L-1of sulfuric acid and extractable perfectly by n-butyl alcohol, molybdenum quantity is obtained by measuring the arsenic in organic phase in term of the stoichiometric relationship between arsenic and molybdenum. Under the optimized condition, the result shows that the linearity between the concentration of molybdenum and its fluorescence intensity is0.09-15μg·L-1, and the relative standard deviation is2.3%, the limit of detection is0.09μg·L-1.The method has been applied to the determination of molybdenum in tea samples, the recoveries are in the range of95.2%-96.9%.An analytical method for indirect determination of molybdenum in Chinese herbal medicine samples is established using atomic fluorescence spectrometry (AFS) with same approach as above. The complex between asenic and molybenum is extracted by n-butyl alcohol, then, the organic solvent is evaporated with heat, and dissoved with hydrochloric acid, arsnic is determined on behalf of molybdenum. The experimental results show that the linearity between the concentration of molybdenum and its fluorescence intensity is0-15μg·L-1with coefficient of0.9984. A standard solution of certain concentration of molybdenum is determined11times, a relative standard deviation of1.1%is calculated based on a statistic method, consequentely, from three times of the standard deviation limit of detection is calculated as0.44μg·L-1. The method has been applied to the determination of molybdenum in Chinese herbal medicine samples, the recoveries are in the range of95.6%-101.3%.