Establishment Of The Methods For Rice In Selenium Speciation Analysis

Selenium(Se),an essential trace element, is vital to human and animals fortheir growth and development. Selenium deficiency will affect human health,resulting in a number of diseases such as Keshan disease, Kashin-Beck disease, etc.Intake Selenium too much will cause selenium poisoning. Therefore selenium intakemust be in a limited range, not too low nor too much. There are many areas in Chinabelong to the selenium deficiency areas so that selenium biofortification is veryimportant. Currently on the market there are many selenium selenium-enrichedproducts, but may not necessarily meet the human needs. It is required to establish asystem of selenium content and selenium speciation detection analysis method todeterminate these selenium-enriched products, in order to standardize theselenium-enriched products market.This study is mainly based on rice as a sample, and establishes a rapid andaccurate, simple, reliable, low-cost content of selenium and selenium speciationmeasurement and analysis techniques. Also the distribution of selenium in rice wasverified and studied of selenium transfer via foliar application in selenium-enrichedrice, in order to provide the scientific basis for the feasibility of Selenium enrichedrice.The main findings are as follows:(1)Establish a method for determination of total selenium (Microwave Digestion-Atomic Fluorescence Spectrometry)Optimized atomic fluorescence spectrometer instrument conditions, optimumconditions:5%hydrochloric acid is the carrier, and20g/L solution of sodiumborohydride as reducing agent, photomultiplier tube negative high voltage is260V,the lamps current of is50mA, atomizer height is8mm. And the conditions of thesepre-treatment conditions such as microwave digestion and hydrochloric acid wereoptimized, the more complex the sample composition is,the more digestion reagentsand long digestion time required and more complex procedures need to be setted.Hydrochloric acid reduction of the heating temperature must be below120°C, thetime required for about18h (including drive away acid time). The lowest instrumentdetection limit is0.8×10-4μg/L, and the relative standard deviation (RSD) is0.4239%.Selenium-enriched rice spiked recoveries is93%to94%. The selenium content of ordinary rice is about80~90μg/kg, and the selenium-enriched rice contents in150~160μg/kg. Highest selenium content is rice bran, followed by rice husk and rice.(2)To study the effect of selenium enrich in riceMicrowave digestion-atomic fluorescence was used to the determination ofselenium content in various parts of the selenium-enriched rice plants, and to thestudy of the effect of selenium enrich in rice. Roots contained the highest selenium,and rice bran was followed, milled rice flour was the last.After foliar seleniumfertilization, selenium was transferred into the plant internal by foliar stomata, andthen transported into paddy internal by stem, while the roots absorbed selenium in thesoil. Rice starch, fat and protein content were measured, while simultaneouslydetermined the selenium content of them,which learned that protein content is verylow but selenium has been mainly concentrated in them. Owing to protein content inrice bran was higher than that in milled rice, selenium content in rice bran was higherthan white rice.(3)To establish the determination method of inorganic selenium and organicselenium (dilute extract-atomic fluorescence)Inorganic selenium (SE (Ⅳ), SE (Ⅵ)) is a water-soluble substance, extractedwith dilute hydrochloric acid, extraction conditions were optimized through singlefactor experiment and orthogonal experiment (L9(34)), The suggested optimalconditions are a volume-weight ratio of4:1,0.1mol/L HCl, an extraction time of8hand a temperature of40℃. Acid extraction solution of selenium-enriched rice on theatomic fluorescence determined SE (Ⅳ),and then by hydrochloric acid reduction ormicrowave digestion of Acid extraction solution, which determined inorganicselenium, soluble state total selenium content, respectively, by subtraction SE (Ⅵ),organic selenium, insoluble forms of selenium, the soluble state organic seleniumcontent was obtained. The advantage of this method verified the presence of seleniumwas organic selenium in selenium-enriched rice mainly, SE (Ⅳ)was about16%of thetotal selenium content, SE (VI) was about7%, and the organic selenium wasapproximately80%.(4)Determination of organic selenium compounds (pre-column derivative-HPLCmethod)As the organic selenium mainly presents in protein, protein extraction ofselenium-enriched rice was carried out, rice protein as a substrate can increase theprobability of detection of organic selenium compounds, has advantages for analysis of the organic selenium compounds in the selenium-enriched rice. First a mid acidhydrolysis and extraction method was established, the suggested optimal conditionsare10g protein with100ml of6mol/L HCl solution, a constant temperature of50℃,extraction time of48h. Followed by the establishment of a pre-columnderivatization-HPLC method for the detection of organic selenium compounds which4-chlorine-3,5-dinitrobenzotrifluoride (CNBF) was the derivatizing agent. Organicselenium compounds in selenium-enriched rice were mainly selenomethionine (SeMet)which contented for4.122μg/g in protein, accounting for65.29%of the seleniumcontent.