Validação de método volumétrico para quantificação de ácido cinâmico em matéria-prima

Abstract

Method validation is described as the process of proving that an analytical method is acceptable for the intended purpose, and is therefore included in the area of quality control. Cinnamic acid (CA) is a phenolic compound, found abundantly in nature, which is gaining prominence in the scientific field due to studies into its antioxidant, antiinflammatory, antimicrobial and photoprotective activities, among others. However, there are no analytical methods for determining CA in official compendia and the methods found in the literature, whether validated or not, are expensive. Volumetry is a classic analytical method that provides quantitative and accurate data quickly, as well as being low cost to perform and maintain. The aim of this work is to develop and validate an alternative analytical method using the volumetric technique for the determination of cinnamic acid. The method was developed using neutralization volumetry, given that CA is an organic acid with low solubility in aqueous media. It was dissolved in 95% ethanol, using 0.1 M sodium hydroxide (NaOH) as a titrant and potassium biftalate (KHP) to standardize the solution, both with a stoichiometric balance (1:1). The end point was monitored visually based on the change in color of the medium. In preliminary experiments, phenolphthalein was chosen as the best indicator. The methodology was validated according to the parameters recommended in ANVISA's RDC 166 of 2017, in which the following parameters were assessed: selectivity, linearity, limit of detection (LOD), limit of quantification (LOQ), precision, accuracy and robustness. The method developed proved to be selective against some pharmaceutical excipients. The method was linear and homoscedastic based on the evaluation of the correlation coefficient (>0.99) and the Cochran test, respectively. The scatter plot of the linearity residuals showed a random distribution of points ± 3 SD, indicating no trends. A LOD of 2.88mg and a LOQ of 9.61mg were obtained. The relative standard deviation and recovery values obtained in the precision, accuracy and robustness tests were less than 2% and close to 100%, respectively. In this way, a selective, precise, linear, accurate and robust method was developed for the determination of cinnamic acid in raw materials using the volumetric technique, which provides the scientific community with an alternative, fast and low-cost method that can be easily reproduced, which contributes to monitoring the quality of these products.