跳至主要内容

Spectrophotometric Determination of the pKa, Isosbestic Point and Equation of Absorbance vs. pH for a Universal pH Indicator

Read full paper at:
http://www.scirp.org/journal/PaperInformation.aspx?PaperID=52618#.VJzCWcCAM4

The pKa and the isosbestic point of the universal pH indicator Carlo Ebra 1-11 (catalog number 45712) were determined using UV-Vis spectrophotometry. Aqueous buffer solutions with pHs ranging from 3.83 to 10.85 were mixed. Four methods—two graphical and two mathematical— were used to estimate the acid dissociation constant (pKa) and isosbestic point using absorbance measurements. The equation for the dependence of the absorbance on pH at λ = 600 nm was obtained using calibration curves. The resulting average pKa of the four methods was 8.277 with a standard deviation of 0.1728. The results obtained using the mathematical methods were very similar, with a deviation of 0.0014; the average pKa determined using these methods was 8.263 ± 0.001. The literature contains no previous reports of the pKa of this indicator. The isosbestic point occurs at a wavelength of 494 nm, with an absorbance of 0.46.
Cite this paper
Salgado, L. and Vargas-Hernández, C. (2014) Spectrophotometric Determination of the pKa, Isosbestic Point and Equation of Absorbance vs. pH for a Universal pH Indicator. American Journal of Analytical Chemistry, 5, 1290-1301. doi: 10.4236/ajac.2014.517135. 
 

[1] Zscherp, C., Schlesinger, R., Tittor, J., Oesterhelt, D. and Heberle, J. (1999) In Situ Determination of Transient pka Changes of Internal Aminoacids of Bacteriorhodopsin by Using Time-Resolved Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy. Biophysics: Proceedings of the National Academy of Sciences, 96, 5498-5503.
[2] Baran, Y., Baran, S. and Kemal, N. (1997) Spectofotometric Determination of the pKa Values of Some Aminoacid Complexes of Pentacyanoferrate (II) and Pentacyanoruthenate (II). Journal of Chemistry, 21, 105-110.
[3] Meloun, M., Bordovská, S. and Vrana, A. (2007) The Thermodynamic Dissociation Constants of the Anticancer Drugs Camptothecine, 7-Ethyl-10-hydroxycamptothecine, 10-Hydroxycamptothecine and 7-Ethylcamptothecine by the Least-Squares Nonlinear Regression of Multiwavelength Spectrophotometric pH-Titration Data. Analytica Chimica Acta, 584, 419-432.
http://dx.doi.org/10.1016/j.aca.2006.11.049
[4] Meloun, M., Bordovská, S. and Galla, L. (2007) The Thermodynamic Dissociation Constants of Four Non-Steroidalanti-Inflammatory Drugs by the Least-Squares Nonlinear Regression of Multiwavelength Spectrophotometric pH-Titration Data. Journal of Pharmaceutical and Biomedical Analysis, 45, 552-564.
http://dx.doi.org/10.1016/j.jpba.2007.07.029
[5] Mitchell, R.C., Salter, C.J. and Tam, K.Y. (1999) Multiwavelength Spectrophotometric Determination of Acid Dissociation Constants Part III: Resolution of Multi-Protic Ionization Systems. Journal of Pharmaceutical and Biomedical Analysis, 20, 289-295.
http://dx.doi.org/10.1016/S0731-7085(99)00041-2
[6] Tam, K.Y., Hadley, M. and Patterson. W. (1999) Multi-wavelength Spectrophotometric Determination of Acid Dissociation Constants Part IV: Water-Insoluble Pyridine Derivatives. Talanta, 49, 539-546.
http://dx.doi.org/10.1016/S0039-9140(99)00010-7
[7] Amador-Hernández, J., Rojas-Hernández, A. Madaí, E., De La Garza-Rodríguez, M., Velázquez-Manzanares, M. and Medina-Vallejo, L.F. (2014) New Chemometric Strategies in the Spectrophotometric Determination of pKa. European Journal of Chemistry, 5, 1-5.
http://dx.doi.org/10.5155/eurjchem.5.1.1-5.901
[8] Ivanov, V.M., Adamova, E.M. and Figurovskaya, V.N. (2010) Acid-Base, Spectrophotometric, and Colorimetric Properties of 1, 2-Dihydroxyantraquinonone3-sulfoacid (Alizarin Red S). Journal of Analytical Chemistry, 65, 473-481.
http://dx.doi.org/10.1134/S1061934810050072
[9] Kong, X., Zhou, T., Liu, Z. and Hider, R.C. (2007) pH Indicator Titration: A Novel Fast pKa Determination Method. Journal of Pharmaceutical Sciences, 96, 2777-2783.
http://dx.doi.org/10.1002/jps.20959
[10] Meloun, M., Bordovská, S., Syrovy, T. and Vrána, A. (2006) Tutorial on a Chemical Model Building by Least-Squares Non-Linear Regression of multiwavelength Spectrophotometric pH-Titration Data. Analytica Chimica Acta, 580, 107- 121.
http://dx.doi.org/10.1016/j.aca.2006.07.043
[11] Meloun, M., Bordovská, S. and Syrovy, T. (2007) A Novel Computational Strategy for the pKa Estimation of Drugs by Non-Linear Regression of Multiwavelength Spectrophotometric pH-Titration Data Exhibiting Small Spectral Changes. Journal of Physical Organic Chemistry, 20, 690-701.
http://dx.doi.org/10.1002/poc.1235
[12] Meloun, M., Ferencíková, Z. and Vrána, A. (2011) Determination of the Thermodynamic Dissociation Constant of Capecitabine Using Spectrophotometric and Potentiometric Titration Data. Journal of Chemical Thermodynamics, 43, 930-937.
http://dx.doi.org/10.1016/j.jct.2011.01.012
[13] Panigrahi, S., Suna, P. and Misra, P.K. (2012) Effect of Organized Assemblies, Part VIII: Spectrophotometetric Study on the Effect of Micellar Media on the pK of Some Substituted N-Benzylideneanilines. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 415, 349-357.
http://dx.doi.org/10.1016/j.colsurfa.2012.08.051
[14] Zapata, L., Kalembkiewicz, J. and Sitarz-Palczak, E. (2009) Studies on Equilibrium of Anthranilic Acid in Aqueous Solutions and in Two-Phase Systems: Aromatic Solvent-Water. Biophysical Chemistry, 140, 91-98.
http://dx.doi.org/10.1016/j.bpc.2008.11.012
[15] Smith, S.A. and Pretorius, W.A. (1994) Spectrophotometric Determination of pKa Values for Fluorescein Using Activity Coefficient Corrections. Water SA, 28, 395-402.
[16] Skoog, D. and Leary, J. (1994) Análisis Instrumental. McGraw-Hill, Madrid.
[17] Harris, D.C. (1999) Quantitative Chemical Analysis. W.H. Freeman, New York.
[18] Vogel, A. (1969) Química Analítica Cuantitativa: Teoría y Práctica. Editorial Kapelusz, Buenos Aires.                           eww141226lx
标签：

评论

发表评论

此博客中的热门博文

Does Immigration Promote the Investment of the Monopolistic Firm?

In the present paper, we examine the effect of increasing uncertainty of immigrants’ growth on the optimal timing of investment of a firm that has a monopolistic power over the labor market. It is revealed that when the uncertainty of immigrants’ growth is more than a threshold level, increasing uncertainty of immigrants’ growth accelerates the optimal timing of firms’ investment and enhances the economic growth, even if the uncertainty of immigrants’ growth is formulated by the geometric Brownian motion, which is in sharp contrast to the standard result that an increase in the uncertainty postpones the optimal timing. With an increase in the immigrants over the past ten years, workforces in the host countries have been growing significantly to the extent that the immigrants represent 70% of the increase in the workforce in Europe, and 47% in the United States as OECD indicates. In the present paper, we attempted to investigate the effect of increased uncertainty caused by the growi...
发表评论
阅读全文

Education Policy Implementation: A Mechanism for Enhancing Primary Education Development in Zanzibar

Education is one of the fundamental rights of individuals; therefore, the government of a country needs to develop and strengthen educational policy and quality as well as to ensure that everyone has equal access to basic education. The improvement of access and quality of education in the world is becoming as an essential factor in development, whereas the basic education (primary school), is acknowledged as a foundation of the higher educational development for every country. To fulfill this goal, governments introduce several policies and procedures; however, it requires some reforms and participation from the politician, policymakers, and other stakeholders to re-examine educational policy so that it can lead to multiplication and betterment of the reforms. Educational reforms actually focus on accountability. A positive educational development and reform is very challenging and needs more effort and strategy on how to use and utilize the resources effectively as such it can achie...
发表评论
阅读全文