Purity determination and uncertainty evaluation of L-selenium-methylselenocysteine

In our country, sodium selenite and sodium selenate are still used as nutritional fortifiers of selenium. Both of them are inorganic selenium, the absorption effect of human body is lower, the risk of toxic wind is larger, and it is easy to cause selenium poisoning. L-selenium-methylselenocysteine (L-SeMC) is a good source of organic selenium, which has higher biological activity and availability. At present, L-SeMC solid standard materials have not yet been developed, a high accuracy and low technical requirement method is needed to determine the purity of candidate reference materials (RMs). In this way, the key steps in the development of reference materials can be completed, and provide a source of high quality selenium supplement for people. In this paper, the candidate structures were identified and analyzed by high performance liquid chromatography (HPLC), Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR). Homogeneity, together with stability were also measured by HPLC. The sample can be transported for a short period of one month under normal conditions, which can also be stored for a long time within the temperature range of −20 °C to room temperature for more than one year. The purity of L-SeMC measured by mass balance method and quantitative nuclear magnetic resonance (qNMR) was 99.5 % with an expanded uncertainty of 0.4 % (k = 2). However, differential scanning calorimetry (DSC) was not suitable for the purity determination of L-SeMC samples. This method has a wide range of applications and may provide a reference for the purity determination of other RMs.