Electrochemical Determination of Titratable Acidity for the Discrimination of Schisandrae Chinensis Fructus and Schisandrae Sphenantherae Fructus.

A simple electrochemical procedure has been developed for determining the titratable acidity in Schisandrae Chinensis Fructus (SCF) and Schisandrae Sphenantherae Fructus (SSF) by means of reduction of quinone in the presence of acid compounds. To measure a voltammogram, a test solution was prepared by mixing a water extract from SCF or SSF and an electrolyte cocktail containing 3,5-di-tert-butyl-1,2-benzoquinone and NaCl. The quantitative results of titratable acidity in the SCF and SSF samples by the present voltammetry were in good agreement with those by neutralization titration using 0.1 M NaOH (r = 0.980): y = 1.003x + 0.010, where the y- and x-axes were the titratable acidity obtained by the present voltammetry and the neutralization titration, respectively. Further, the titratable acidities in the SSF samples were significantly lower than those in the SCF samples (p < 0.01). From these findings, we show that the titratable acidity is useful as an indicator to discriminate between SCF and SSF. Moreover, a prototype of electrochemical portable sensor for on-site analysis has been provided to perform this procedure.