Standards and Samples

The spectrophotometric methods for analyzing Mn and for analyzing glucose use a chemical reaction to produce a useful signal. In the analysis for Mn in steel, colorless Mn²⁺ is oxidized to give the purple MnO₄^– ion, while in the analysis for glucose, colorless glucose is used to reduce the yellow Fe(CN)₆^3- ion to the colorless Fe(CN)₆^4- ion. In the analysis for manganese no attempt is made to precisely control either the time or temperature at which the reaction occurs, and samples and standards are treated separately.  The glucose analysis, however, requires that all samples and standards be treated simultaneously at exactly the same temperature and for the same length of time. Briefly explain why these experimental procedures are so different.