Quinizarin characterization and quantification in aqueous media using UV-VIS spectrophotometry and cyclic voltammetry

• Published in: Dyes and pigments 2021-01, Vol.184, p.108641, Article 108641
• Main Authors: Rivas-Sánchez, A.K., Guzmán-Hernández, D.S., Ramírez-Silva, M.T., Romero-Romo, M., Palomar-Pardavé, M.
• Format: Article
• Language: English
• Subjects: Acidity constants; Cyclic voltammetry; Inclusion complex; Quinizarin; Spectrophotometry
• ISSN: 0143-7208; 1873-3743
• DOI: 10.1016/j.dyepig.2020.108641

This work reports for the first time, the acidity constant (pKa) values, in aqueous media, of four anthraquinones, namely: quinizarin (pKa1 = 10.83 ± 0.02, pKa2 = 12.03 ± 0.02); anthrarufin (pKa1 = 10.93 ± 0.02, pKa2 = 12.49 ± 0.02); chrysazine (pKa1 = 8.73 ± 0.01, pKa2 = 12.37 ± 0.01) and anthraflavin (pKa1 = 7.47 ± 0.03, pKa2 = 8.48 ± 0.03), and the quinizarin inclusion complex formation constant with 2-hydroxy-propyl-β-cyclodextrin, pKf = 2.53 ± 0.04, as well. Furthermore, it is shown that this supramolecular inclusion complex resulted convenient to perform quinizarin electrochemical quantification, in aqueous media at pH 7.00, by means of cyclic voltammetry attaining the following analytical performance: (3.129 ± 1.200) μM and (10.429 ± 1.133) μM were the detection and quantification limits, respectively, with a sensibility of (0.213 ± 0.006) μA μM−1 and a (0–36) μM linear interval. Analogously, UV–Vis spectrophotometry allowed determining quinizarin, under the same conditions, with the following analytic parameters: a detection limit of (1.411 ± 0.586) μM, quantification limit of (4.706 ± 0.551) μM, with (0.00547 ± 0.0001) abs μM−1 sensibility and a (0–29) μM linear interval. Moreover, it is shown that cyclic voltammetry determined quinizarin in presence of anthrarufin, chrysazine and anthraflavin as interferents, contrary to the spectrophotometric method [Display omitted] •Quinizarin, anthrarufin, chrysazin and anthraflavin were studied.•pKas, in aqueous media, of 4 hydroxylated anthraquinones, HA, were quantified.•Quinizarin and 2-hydroxy-propil-β-cyclodextrin inclusion constant was determined.•Electrochemical quinizarin quantification in aqueous medium is reported.•Quinizarin was selectively quantified in the presence of 3 different HA.