Speciation Analysis Method Of Iodine In Kelp And The Stability Of Iodine Source

Salt iodization is the fastest,most effective and convenient intervention to prevent iodine deficiency disorders.There are many kinds of iodine additives,but the forms of iodine contained in them are unknown.The national/industry standard is also about the determination method of total iodine content.The analysis of kelp iodine content is mainly focused on total iodine concentration.It is scarce for the rapid and sensitive analytical method of iodine species corresponding to iodate,iodide,MIT and DIT.This thesis aims at the problems of iodine form and current status of iodine addition in salt,the extraction and separation of various iodine forms in kelp,and the stability of iodine source in algae juice were carried out.The main solutions are as follows:（1）On the basis of exploring the pretreatment methods of enzymatic hydrolysis of kelp,a rapid determination method of high-performance liquid chromatography and inductive l y coupled plasma mass spectrometry for different iodine species existed in kelp samples was established.After comparing the enzymatic hydrolysis performances for kelp,trypsin was selected as the adequate type of enzyme for the pretreatment under 50℃for 10 hours of digestion.Then the extraction solution was obtained by centrifugation and filtration for iodine speciation analysis.After a series of optimizing experiments on the chromatograp hic separation with the Dionex Ion Pac AS14 type of anion separation column（4 mm×250 mm）,the optimum column separation conditions are that the gradient elution with 0.1 mol/L（NH₄）₂CO₃ at p H=9 is used as a mobile phase.Flow rates before 1500 s and after 1800 s are 0.8 and 1.2 m L·min^-1,respectively.The linear ranges of the standard calibrations on four iodine species are wide(1.0～150μg·L^-1),and the detection limits are 1.62,1.02,1.59 and2.55μg·L^-1,respectively while the RSD values of four iodine species are all less than 2%.This analytical method established in this work has been successfully applied for different iodine speciation analyses in kelp.（2）The fresh seaweed was extracted by alkaline extraction and water extraction technology commonly used in the industrial extraction of kelp.The original solution of seaweed juice and the sample after adding standard were analyzed and determined by HPLC-ICP-MS.The conclusion was that the main iodine source is potassium iodide with a content of 2.93 g·L^-1.This form has high stability and does not react with other forms of iodine.The two extraction methods used are simple,easy to operate,have a high safety factor,and can achieve the purpose of extracting iodine from kelp.Still the iodine obtained by the extraction is potassium iodide.When water is used as the extraction medium,the time is long,and the temperature requirement is slightly higher;when the alkaline solution is used as the extraction medium,the reaction time is short and the required solution volume is large.（3）The stability of iodine species in algal juice was analyzed and determined by the HPLC-ICP-MS method established above,and influencing factors of storage time,temperature,p H and ionic strength were explored respectively,and then the follow ing conclusions were drawn:the inorganic iodine is stable and will not change within one month;the iodine is relatively stable at 4°C,27°C,and 37°C,it will not undergo a morphologica l transformation and content change.The most obvious difference is that after boiling for 5minutes,iodine changes both in form and in content.Iodine in the algae juice is unstable and easily converted in acidic environments.It can be combined with sodium chloride,and the concentration of sodium chloride does not affect the existence of the iodine source.