Method For Analysis Of The Speciations Of Selenium In Vegetal Food

Selenium is one of the necessary microelements to human beings, with its tiny content in the environment and plant. It has significant biological implications to us. It is not fit to judge the nutrition and toxicity of selenium by the content of total selenium, owing to the significant relevance between its availability and speciations. So it is necessary to establish and extend the method for speciation analysis of selenium. Choosing four speciations of selenium with significant biological meanings, this paper has given a method for the determinations of speciations of selenium in vegetal food with HPLC-HG-AFS techniques. The results are as follows:1. The objects of this study has great representativeness. We clsssify the vegetal food according to the nutrition, toxicity, absorbtion of selenium and choose the samples of cruciferae,liliaceae,leguminosae etc to do the analysis. We have done this as many as we could.2. Establish a better extraction method. Among the four extractions including boiling water extraction, perchloric acid-ethanol extraction, methanol-water extraction, enzyme extraction, methanol-water extraction is better.3. Establish the better parameters of the instrument. Of the HPLC part, the mobile phase should be (NH4)2HPO4,60 mmol/L, with its pH being 5.5; Of the HG part, reducing ageats should be 1.5%KBH4(m/v)+0.5%KOH (m/v)+0.1%KI (m/v) and the carrier solution. 15%HCl(v/v); Of the AFS part, selenium hollow cathode lamp current should be 45 mA: the negative high voltage of photomultiplier tube should be 300V; the flow rate of carrier gas should be 400 mL/min, and the flow rate of make up gas,600 mL/min.4. Assessments of the method:Detections of SeCys, Se(Ⅳ) SeMet, Se(Ⅵ) are respectively 6.29-6.46μg/L,5.46-5.57μg/L,17.15-17.99μg/L,7.56-7.90μg/L; Seven determinations of the same standard solution containing four speciations of selenium showed that the RSDs of the retention times and peak areas are as follows:SeCys 0.6%, 2.6%; Se(Ⅳ) 0.1%,2.6%; SeMet0.8%,2.5%; Se(Ⅵ) 0.2%,4.7%; The linear correlation coefficients of the four speciations between the peak areas and concentrations are satisfactory, all above 0.999. 5. Applications of the method. The method was applied to vegetal food as many as possible and the results showed that the content of selenium is rather low in most samples, with no speciation of selenium being detected. Only in peanut and soybean were tiny speciations of selenium detected. Meanwhile, it is found that the contents of selenium in some "selenium-riched" food do not match their labels. In other word, the real value of selenium content maybe very low.