Modeling of rutin species distribution and molybdate complex forming in reaction with Folin-Ciocalteu (F-C) reagent using PHREEQC tool

Abstract

PHREEQC is a computer program developed by the US Geological Survey (USGS) and has become the standard for water chemistry. At present PHREEQC is implementing in biochemistry and environment science where a computational tool is needed. This study is an attempt to model the distribution of rutin species at different pH, acidic pH shifting after addition of sodium bicarbonate instead of sodium carbonate and molybdate-rutin complex formation in F-C reagent. This study used a simplified model of pH 6.8 rutin solution with 5 species H4Rut, H3Rut-, H2Rut2-, HRut3- and Rut4- corresponding to pKa values. Reaction mixture reaches pH 10.63 value by mixing 0.311 M sodium carbonate solution, 0.5 mg/mL rutin solution and 2 N Folin-Ciocalteu reagent with prescribed proportions 30:1:1 [1, 2]. At pH value 10.63 anionic rutin species H3Rut- (1%), H2Rut2- (12 – 98%), HRut3- (1 – 54%) dominate depending on pKa constants [3–5]. Neutral species H4Rut is minor (less than 0.001%). Two molybdate-rutin complex constants pK1 = -8.01 and pK2 = -3.14 were used [6]. An alkaline environment is critical to the reaction [7]. Alkaline pH is reached by adding sodium carbonate [8]. Complexes forming below pH value 6.0 was not taken into consideration by the simplified model. Computation result of 3rd model revealed that at relatively wide pH interval (8 – 11) a concentration of molybdate-rutin complex is within the range of 26.88 – 27.0 μM, and approximately 99.98 – 99.99 % of the total rutin amount was found in the form of molybdate-rutin complex.