Determination of Glycyrrhizic Acid by Methyl Violet Dual-wavelength Superimposed Visible Spectrophotometry and its Analytical Applications

Abstract

An indirect determination method for glycyrrhizic acid in health foods was established using a dual-wavelength superposition visible spectrophotometric technique. The method relies on the reaction between diammonium glycyrrhizinate and the cationic dye methyl violet. In Clark-Lubs buffer solution at pH 3.0, diammonium glycyrrhizinate transforms into glycyrrhizinate, forming supramolecular aggregates with methyl violet through hydrogen bonding. This results in positive and negative absorption peaks in the visible region, with the maximum positive absorption occurring at 564 nm and the sub-maximum negative absorption at 676 nm. The respective molar absorption coefficients are 2.77×105 L/(mol·cm) and 1.53×105 L/(mol·cm). However, when utilizing the dual-wavelength superposition method, the molar absorption coefficient becomes 4.28×105 L/(mol·cm). The linear range for diammonium glycyrrhizinate determination is 1.00–2.50 mg/L, with a correlation coefficient of 0.9997 and a detection limit of 0.54 mg/L. This proposed method offers an indirect means to determine the glycyrrhizic acid in health foods. The measured values' relative standard deviation (n = 6) was consistently within 5%, indicating satisfactory results.