Inter-Laboratory Analysis of Steviol Glycosides by an External Standard Method

Abstract

To optimise steviol glycoside analysis, several round-robin tests were organised by the European Stevia Association (EUSTAS). Seventeen laboratories participated in the testing. Only 8 laboratories have sent their results. In the first round-robin testing, 2 samples were analysed. The first sample had a purity of 96.2%. The second sample was a 4/5 dilution with NaHCO 3 of sample 1. This way, the drying process itself could be checked. The purity of sample 2 was 82.35%. The reported purities of sample 1 varied between 79.8 and 96.2%, those of sample 2 varied between 58.1 and 81.8%. The drying of sample 2 showed that weight loss was between 4.9 and 12.7%, demonstrating that not all laboratories dried the sample to a constant weight. In a second round-robin testing, the purity of the sample was 91.1%. The reported purities of the sample varied between 82.74 and 95.86%. About 3% purified RebB was added to the sample to check the quality of the analysis of this compound possessing a carboxylic group. The samples contained the following steviol glycosides: Reb D, Reb E, Reb A, ST, Reb F, Reb C, Dul A, Reb G, Rub, Reb B, SB and SM (1 lab). No SV was detected. The number of SVgly analysed in the different laboratories varied between 4 and 11. One lab only analysed ST and Reb A and gave a percentage composition of these compounds. To improve the accuracy of analysis, different suggestions are made, such as controlling the drying process of samples and standards, purity of standards, injection of sufficient material and use of solvent gradients to shorten the run time and to reduce integration errors. The results of this second round-robin tests are better than those of the first one.