Study On The Method Of Selenium Speciation Analysis In Food

Selenium,a trace element necessary for the human body,is extremely complex in its different chemical forms.Its anti-oxidation and immune-enhancing biological functions exert an important impact on human health.Selenium is known to form both volatile/non-volatile(physical property)and inorganic/organic(chemical property)compounds in environmental and biological systems.Inorganic selenium is highly toxic with low biological activity,while organic selenium is lowly toxic with high bioabsorption and utilization rate.Therefore,selenium is a necessary trace element in the human body with a suitable range similar to poisoning limit.The research and development of quantitative determination methods of chemical form of selenium in food have great practical value for the effect of selenium on human health.(1)With divinylbenzene(DVB)-carbon molecule(CAR)-polydimethylsiloxane(PDMS)as the adsorption coating of solid phase micro-extraction,and optimized extraction factors of extraction time,extraction temperature,stirring speed and ionic strength,a new method to determine the volatile organic selenium(dimethyl selenide [DMSe] or dimethyl diselenide [DMDSe] in foods)was developed by a combination of headspace solid phase microextraction and gas chromatography-mass spectrometry.The detection limits of DMSe and DMDSe were 57.0 and 13.2 ng/L,and the relative standard deviations(RSDs,n=7)were 8.5% and 7.1%.The method was applied to the analysis of DMSe and DMDSe in foods such as drinking water,juice,garlic and onion,and the standard addition recovery was carried out.The recovery of standard addition was 84.6~102.5%,and the relative standard deviations(RSDs,n=3)was 7.1~9.4%,which was suitable for the determination of volatile organic selenium in food.(2)A new method was developed to determine inorganic selenium(Se(IV)and Se(VI))in food by a combination of hollow fiber membrane liquid phase microextraction and graphite furnace atomic absorption spectrometry.The factors affecting the extraction efficiency of hollow fiber membrane liquid phase microextraction were investigated and optimized.Under the optimal extraction conditions,the Ammonium Pyrrolidine Dithiocarbamate(APDC)complexing agent was only chelated with Se(IV)to form metal chelate that was extracted by carbon tetrachloride and separated from Se(IV);the content of Se(VI)was obtained by subtracting the content of Se(IV)from the total selenium content.With this method,the detection limit of Se(IV)was 11 ng/L,the enrichment factor was 400,and the relative standard deviation(RSDs,n=7)was 7.2%.The method was applied to the analysis of inorganic selenium in drinking water and health care products,and the recovery rate of the standard addition was 80-105%.It does not set strict requirements for instruments or equipment with advantages in measuring the total amount of inorganic selenium in food.(3)A method to directly determine organic selenium in food was developed.Ultrasonic extraction of organic selenium was carried out by adding cyclohexane to an aqueous solution with a pH of 7.0.After microwave digestion,the extract was subjected to inductively coupled plasma mass spectrometry to determine the content of organic selenium.Under optimal test conditions,the detection limit of the method was 0.45 ?g/kg,the limit of quantification was 1.5 ?g/kg,and the recovery of standard addition was 93.5-103.0%.The method has the advantages of high precision and wide linear range,which is suitable for direct measurement of the total amount of organic selenium in food.(4)A method was developed for simultaneous determination of six selenium forms such as inorganic selenium and selenium amino acids in food by ultrasonic assisted enzymatic extraction high performance liquid chromatography inductively coupled plasma mass(HPLCICP-MS)spectrometry combination.The factors affecting the separation and extraction of selenium,such as extraction method,mobile phase pH,concentration,methanol content,flow rate and column temperature,were investigated and optimized.Meanwhile,the collision/reaction cell was used to effectively eliminate the interference of composite ions and improve the detection sensitivity.This method achieved complete baseline separation of six target analytes: selenite(Se(IV)),selenate(Se(VI)),elenocystine(SeCys2),selenomethionine(SeMet),Se-methylselenocysteine(MeSeCys)and selenoethionine(SeEt).The detection limit of each substance was 0.012-0.60 ?g Se/L,and the linear range was 3 to 4 orders of magnitude with the relative standard deviation(RSDs,n=7)of 4.0-8.2%.The method was applied to the analysis of selenium forms in food,and the recovery of standard addition was 81.6-108.6%.Simple,convenient,fast,efficient and environmentally friendly with high sensitivity,this method can be used for the quantitative analysis of specific selenium forms in food.