Study Of Trace Iodine In Geological Samples By Two Methods

Iodine is an essential micronutrient element necessary for the synthesis of vitalhormones such as thyroxine(T4) and triiodothyronine(T3), needed for the maintenanceof metabolic rate, cellular metabolism and integrity connective tissue. Lack of thesehormones causes mental retardation and goiter. However, excessive intake of iodine canalso cause several diseases. Intake of iodine can be done from different sources, such aswater, beverages and food. Although several techniques have been proposed for thedetermination of iodine, it is still difficult to analysis it precisely. This work wasperformed to improve the methods for determination of iodine in geological samplessystematically by chloramine T-tetrabase system catalytic spectrophotometry andinductively coupled plasma mass spectrometry. The methods have been applied to thenational standard samples with satisfactory results.Some improvement and further optimization for the catalytic spectrophotometricdetermination of trace iodine in geological samples in chloramine T-4,4’-Tetramethyldiamino-diphenylmethane system with semi-melting sample pretreatment has beendeveloped. The semi-melting sample pretreatment conditions, include Na2CO3-ZnOmixed flux, semi-melting temperature and time, the additive time of Acetic acid andTetrabase，the dosage of chloramine T, chromatogenic time, acidity, temperature, etc,were discussed and several settlement measures were also proposed. This paper alsodiscusses in detail that the iodine species during the analysis process and its effect onthe result. Under the optmized conditions the method provides good selectivity, simpleoperation and low detection limit of0.15μg/g for iodine.Among many kinds of techniques for determination of iodine, inductively coupledplasma mass spectrometry (ICP-MS) is a sensitive analytical technique, allowingprecise and rapid measurement. In this work, a method for determination of trace iodinein geological samples by ICP-MS with semi-melting sanple pretreatment has beendeveloped. The signal response and memory effect of different iodine species indifferent solution mediums was assessed. The result from the experiments show thatammonia solution is a suitable medium for determination of iodine and the diluteammonia solution is a effective way in eliminating the memory effect from iodine. Byadding ethanol and, the method for determination of iodine in geological samples wasestablished using ICP-MS and the method detection limit for iodine was0.001μg/g.The precisions of the methods are found to be in reasonable agreement withanalytical request. It has been shown that they have great potential for the determinationof trace iodine in geological samples.