Bray–Liebhafsky oscillatory reaction as the matrix system for the kinetic determination of microquantities of alizarin and purpurin

Abstract

Two hydroxyanthraquinones, alizarin and purpurin, that have been used throughout history as a natural pigment, were extracted from roots of Rubia tinctorum from Serbia. As substances with important chemical activities and, therefore, with wide applications (for example in dyeing textile fabrics as well as in pharmacy because of their anti-inflammatory, anti-cancer, antiviral, antimicrobial and antioxidant activities, etc.) they were analyzed in the kinetically very sensitive Bray–Liebhafsky (BL) oscillatory reaction. However, although they are both, hydroxyanthraquinones it is shown that their interactions with BL nonlinear reaction system differ significantly. Consequently, two different reactions were used to explain the mechanism of their chemical activities. The numerical simulations based on a standard model of the BL oscillatory reaction together with proposed reactions due to alizarin/purpurin interactions with a matrix are correlated with experimental investigations. Moreover, it is shown that very small amounts of alizarin and purpurin (from about 1 × 10–7 M) produce the response of the BL matrix such that micro-quantitative analysis based on the BL oscillatory reaction can be successfully performed in this reaction system. The linear response of the BL matrix on the presence of alizarin and purpurin (necessary for microquantitative determination) is analyzed as a function of two concentration sensitive parameters: pre-oscillatory period τ1 and potential shift after perturbation ΔE.