The Influence of Initial Carbonate Concentration on the Folin-Ciocalteu Micro-Method for the Determination of Phenolics with Low Concentration in the Presence of Me-thanol: A Comparative Study of Real-Time Monitored Reactions

During the Folin Ciocalteu (F-C) micro-assay for the determination of phenolics in the presence of methanol, fine solids can form. In a previous paper, we hypothesized that the interference from alcohol on the F-C reaction can be minimized depending on the particular procedure used to reach the alkalinity condition. In order to demonstrate our hypothesis we studied, by spectrophotometrically monitoring, the time-behaviour of the reactions carried out in the presence of different methanol concentrations at the same alkalinity condition from two protocols. The results showed that the interfering effect of methanol on the F-C micro-method can be affect and even prevented depending on working conditions. In particular, the formation of fine solids can be delayed, slowed down and prevented depending on the initial carbonate concentration used. We have explained why the initial carbonate concentration, used to reach the final alkalinity condition, plays an important role in the F-C reaction carried out in the presence of methanol. Moreover, the results from real-time monitoring showed that, differently from traditional F-C procedure, our procedure allows us to carry out the F-C micro method in the presence of 6% methanol, as an extreme concentration, reading the absorbance at real time 24 min. The real-time monitoring of absorbance can be considered as a useful means to explore the effect of other parameters on precipitate formation caused by the presence of methanol in the F-C reaction.