Evaluation of Uncertainty for Determination of Stevioside Content in Fermented Milk by HPLC

[Objectives]The paper was to establish an evaluation method for the uncertainty of stevioside(including stevioside,rebaudioside A,rebaudioside B,rebaudioside C,rebaudioside F,Dulcoside A,rubusoside and steviolbioside)content determination in fermented milk based on HPLC.[Methods]The mathematical model of stevioside content and the propagation rate of uncertainty were established,and the sources of uncertainty were analyzed.[Results]The uncertainty mainly came from four main aspects,including standard uncertainty u(C)introduced by solution concentration C,standard uncertainty u(V)introduced by sample volume V,standard uncertainty u(m)introduced by sample mass m weighing and standard uncertainty u(f_(rep))introduced by measurement repeatability of stevioside content after sample dissolution and constant volume.The uncertainty estimation table and fishbone chart of stevioside content X determination were established.The relative synthetic standard uncertainty of stevioside content was obtained,and the standard uncertainty was extended to form the measurement result of stevioside content and its uncertainty report.[Conclusions]The evaluation results can be directly applied to the daily practical detection work.

Methylated and thiolated arsenic species for environmental and health research——A review on synthesis and characterization

Hundreds of millions of people around the world are exposed to elevated concentrations of inorganic and organic arsenic compounds, increasing the risk of a wide range of health effects. Studies of the environmental fate and human health effects of arsenic require authentic arsenic compounds. We summarize here the synthesis and characterization of more than a dozen methylated and thiolated arsenic compounds that are not commercially available. We discuss the methods of synthesis for the following14 trivalent（Ⅲ） and pentavalent（） arsenic compounds： monomethylarsonous acid（MMA~Ⅲ）, dicysteinylmethyldithioarsenite（MMA~Ⅲ（Cys）_2）, monomethylarsonic acid（MMA~Ⅴ）,monomethylmonothioarsonic acid（MMMTAⅤ） or monothio-MMA~Ⅴ, monomethyldithioarsonic acid（MMDTA~Ⅴ） or dithio-MMA~Ⅴ, monomethyltrithioarsonate（MMTTA~Ⅴ） or trithio-MMA~Ⅴ,dimethylarsinous acid（DMA~Ⅲ）, dimethylarsino-glutathione（DMA~Ⅲ（SG））, dimethylarsinic acid（DMA~Ⅴ）, dimethylmonothioarsinic acid（DMMTA~Ⅴ） or monothio-DMAⅤ, dimethyldithioarsinic acid（DMDTA~Ⅴ） or dithio-DMA~Ⅴ, trimethylarsine oxide（TMAO~Ⅴ）, arsenobetaine（AsB）, and an arsenicin-A model compound. We have reviewed and compared the available methods,synthesized the arsenic compounds in our laboratories, and provided characterization information. On the basis of reaction yield, ease of synthesis and purification of product, safety considerations, and our experience, we recommend a method for the synthesis of each of these arsenic compounds.