I am trying to develop a method for the analysis of reducing sugars content in biomass samples in microtitre scale. In particular I am using a modified Nelson-Somogyi method (modified because I am using the Folin-Ciocalteau reagent instead of the arsenic containing nelson reagent). At moment I am mixing together equal volume of sugar solution and copper tartrate solution. After boiling for 20 min, solution is cooled down and 8 volumes of a Folin-Ciocalteau reagent 1: 10 diluted, 1N in acid content, are added and mixed well to dissolve all the cuprous oxide. However, sometimes my standard curve is not linear. Do you have any suggestion to improve my method?