Hemmateenejad Bahram, Abbaspour Abdolkarim, Maghami Homeyra, Foroumadi Alireza
Chemistry Department, Shiraz University, Shiraz, Iran.
Anal Chim Acta. 2008 Jan 28;607(2):142-52. doi: 10.1016/j.aca.2007.11.043. Epub 2007 Dec 3.
Annihilation of the contribution of one chemical component from the original data matrix is a general method in rank annihilation factor analysis (RAFA). However, RAFA is not applicable for studying the protonation equilibria of multiprotic acids. In this work, a two-rank annihilation factor analysis (TRAFA) method was proposed for determination of the acidity constants of diprotic acids. After recording the electronic absorbance spectra of the acids at different pH, the contributions of both H(2)A and A(2-) were annihilated from the absorbance data, which made feasible the determination of two successive acidity constants. The method was validated by analysis of simulated data and its application to the determination of the acidity constants of calmagite, as a reference compound. A close agreement was obtained between the resulted values by TRAFA and the declared values. Indeed, the method was used for determination of the acidity constants of two new chromenone derivatives in binary solvents mixtures of methanol and water. The effects of changing solvent composition on acidity constant data were explained by linear solvation free energy relationships (LSFER) utilizing solvatochromic parameters.
从原始数据矩阵中消除一种化学成分的贡献是秩消除因子分析（RAFA）中的常用方法。然而，RAFA不适用于研究多元酸的质子化平衡。在本工作中，提出了一种双秩消除因子分析（TRAFA）方法来测定二元酸的酸度常数。在记录不同pH值下酸的电子吸收光谱后，从吸收数据中消除H₂A和A²⁻的贡献，这使得连续测定两个酸度常数成为可能。通过对模拟数据的分析及其在作为参考化合物的钙镁试剂酸度常数测定中的应用，验证了该方法。TRAFA得到的值与公布的值非常吻合。实际上，该方法用于测定甲醇和水的二元溶剂混合物中两种新的色酮衍生物的酸度常数。利用溶剂化显色参数，通过线性溶剂化自由能关系（LSFER）解释了溶剂组成变化对酸度常数数据的影响。
