Spectrophotometric determination of acidity constants by two-rank annihilation factor analysis

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• 作者：Bahram Hemmateenejad ; Abdolkarim Abbaspour ; Homeyra Maghami ; Alireza Foroumadi
• 关键词：Rank annihilation factor analysis ; Acidity constant ; Spectrophotometry ; Methanol– ; water ; Chromenone
• 刊名：Analytica Chimica Acta
• 出版年：2008
• 出版时间：28 January 2008
• 年：2008
• 卷：607
• 期：2
• 页码：142-152
• 全文大小：1229 K

文摘

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 H₂A and A²⁻ 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.