Comparison of Two Spectrophotometric Methods for Quantifying Total Hydroxycinnamic Acids in Coneflower (Echinacea purpurea) Preparations

Background & Aim: Hydroxycinnamic acids are one of the most important bioactive substances of Echinacea drugs. These compounds possess immuno-enhancing activity and thus, total hydroxycinnamic acids are mostly used as the main criterion for quality control of Echinacea purpurea and its drugs.  Hence, the quality control of Echinacea requires to developing the reliable methods which are simple and also have a suitable accuracy in measuring total hydroxycinnamic acids.The current study was performed in order to sets a simple method for quantifying total hydroxycinnamic acids of Echinacea and then, comparison of this method which named as the AlCl3 method with the method of European pharmacopoeia (EP). Experimental: Total hydroxycinnamic acids of 10 coneflower samples were determined using AlCl3 and EP methods and the amounts obtained by these two methods, were compared using statistical criterion. Results: Accuracy of AlCl3 method in measuring total hydroxycinnamic acids of Echinacea was not suitable, as the relative difference between amounts measured by this method and those measured by EP method was 50-130%. Comparison of this method with EP method indicated that performance of AlCl3 method for quantifying total hydroxycinnamic acids of Echinacea drugs was very poor and low value of willmott index of agreement (d= 0.53) and high value of relative error (RE= 0.83) were obtained. Recommended applications/industries: Due to non-selective reaction of Al(III) with hydroxycinnamic acids, the AlCl3 method is not suitable for measuring the total hydroxycinnamic acids of Echinacea and its preparations.