Fig. 3
Standard series are required for reproducibility of the microbiological assay. The vitB1 thi6 microbiological assay was used on a 353 nM thiamin aqueous test solution. Each analysis day (17 h assay incubation) consisted of a standard series (12 concentrations, 4 technical replicates, 48 wells in total) and 24 technical replicates of the 353 nM test solution (24-well plate). The box plots show the median and quartiles, where X represents the mean. Measurements, including outliers, are shown as points. The red crossed line indicates the expected, true, concentration of the test sample, 353 nM. Each result is calculated by using the concentration–response curve from the standard series, which is measured in parallel for each analysis day (A). Analyses in which no standard series are included for each day are presented in B. Here, the equation derived from the assay of the first analysis day (box plot on the left) was reused to calculate the test solution in the subsequent analysis days