Development of pure certified reference material of stevioside.

Pure stevioside was extracted from leaves of Stevia rebaudiana (Bertoni) to be used as a reference material in the instrument calibration or method validation process. The mass fraction was determined by comparison between the mass balance method and quantitative nuclear magnetic resonance (qNMR) spectroscopy. The impurities in the sample were analyzed by Karl Fischer titration for moisture content and thermogravimetric analysis for inorganic residue. Homogeneity, together with short term and long term stability, were also studied and the uncertainty was reported. The certified value of this mass fraction is 0.986 ± 0.0019 (k = 2) with 1 year stability.