A new predictive formula for calculation of equilibrium pH: a step back in time
2010; American Physical Society; Volume: 298; Issue: 2 Linguagem: Inglês
10.1152/ajprenal.00240.2009
ISSN1931-857X
Autores Tópico(s)Chemical and Physical Properties in Aqueous Solutions
ResumoLETTERS TO THE EDITORA new predictive formula for calculation of equilibrium pH: a step back in timeE. Wrenn WootenE. Wrenn WootenTexas Radiology Associates, Plano, TexasPublished Online:01 Feb 2010https://doi.org/10.1152/ajprenal.00240.2009MoreSectionsPDF (31 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations to the editor: Nguyen et al. (4) report “the first quantitative approach that can predict the equilibrium [H+] based on the partitioning of H+ buffering among the different buffer pairs in solution.”To claim no previous method could calculate final equilibrium concentrations from starting preequilibrium concentrations is incorrect, since the ability to perform such calculations was achieved over 50 years ago. None of the classic texts on equilibrium calculations by Bjerrum, Ricci, Stumm, Guenther, Butler, or others (1–3, 6, 9) are referenced, but all of these provide better and more general strategies to accomplish the same goal as Nguyen et al.The classic methods published previously utilize half the number of material balance equations advocated by Nguyen et al. and produce exact, but less cumbersome solutions. These approaches obtain the final equilibrium concentrations more directly and written explicitly in terms of starting concentrations. Nguyen et al. also present a simple titration experiment they imply is novel, although equivalent experiments have been performed before (5). Despite the authors' claim of physiological relevance, their equation does not explicitly include the carbon dioxide equilibrium, arguably the most important buffer system physiologically.The authors state that “the Stewart strong ion formulations can only describe (rather than predict) the equilibrium pH,” but the Stewart method (8) for calculating acid-base balance is equivalent to the classic methods (2, 9, 10). They also assert the strong ion difference does not determine a specific proton concentration. For their mixture in Table 3, assuming constant Kw, the strong ion difference, which is numerically equal to the total titratable base, which is numerically equal to the opposite of the total titratable acid, which is numerically equal to the added analytical HCl concentration, which represents the amount of HCl added to the system preequilibrium, will determine the final equilibrium pH (2, 3, 6, 8, 9). Calculation using the Stewart method, or any equivalent relationship, is exact and is predictive. It has also been around for some time. The method Stewart applied to physiology nearly 30 years ago, including the carbon dioxide equilibrium, was known to environmental chemists at least 10 years before that (8, 9).Nguyen et al. may misunderstand the traditional use of these equations in clinical medicine. The interest in calculating variables such as the base excess and strong ion difference from equilibrium concentrations stems from applying equilibrium equations in the most relevant way. As explained by Siggaard-Andersen and Fogh-Andersen (7), the goal of equilibrium calculations such as the base excess approach or Stewart method in current clinical acid-base assessment is to quantify and characterize the metabolic component of an acid-base disorder, not to calculate final buffer concentrations or pH as implied by the authors. In summary, Nguyen et al. should be congratulated for their interest in applying rigorous chemical principles to physiology, but they have basically taken a step back in time to over a half century ago.REFERENCES1. Bjerrum J. Metal Ammine Formation in Aqueous Solution. Copenhagen, Denmark: P. Haase, 1941.Google Scholar2. Butler JN. Ionic Equilibrium: Solubility and pH Calculations. New York: John Wiley and Sons, 1998.Google Scholar3. Guenther WB. Unified Equilibrium Calculations. New York: Wiley, 1991.Google Scholar4. Nguyen MK , Kao L , Kurtz I. Calculation of the equilibrium pH in a multiple-buffered aqueous solution based on partitioning of proton buffering: a new predictive formula. Am J Physiol Renal Physiol 296: F1521–F1529, 2009.Link | ISI | Google Scholar5. Ramette RW. Chemical Equilibrium and Analysis. Reading, MA: Addison-Wesley Publishing, 1981.Google Scholar6. Ricci JE. Hydrogen Ion Concentration: New Concepts In a Systematic Treatment. Princeton, NJ: Princeton Univ. Press, 1952.Crossref | Google Scholar7. Siggaard-Andersen O , Fogh-Andersen N. Base excess or buffer base (strong ion difference) as a measure of a nonrespiratory acid-base disturbance. Acta Anaesthesiol Scand 39, Suppl 107: 123–128, 1995.Crossref | ISI | Google Scholar8. Stewart PA. Modern quantitative acid-base chemistry. Can J Physiol Pharmacol 61: 1444–1461, 1983.Crossref | PubMed | ISI | Google Scholar9. Stumm W , Morgan JJ. Aquatic Chemistry. An Introduction Emphasizing Chemical Equilibria In Natural Waters. New York: Wiley-Interscience, 1970.Google Scholar10. Wooten EW. Analytic calculation of physiological acid-base parameters in plasma. J Appl Physiol 86: 326–334, 1999.Link | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: E. Wrenn Wooten, Texas Radiology Associates, L.L.P., 1820 Preston Park Boulevard, Suite 1200, Plano, TX 75093 (e-mail: [email protected]com). Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation Cited ByEquilibrio ácido-base: el mejor enfoque clínicoRevista Colombiana de Anestesiología, Vol. 43, No. 3Acid–base equilibrium: The best clinical approachColombian Journal of Anesthesiology, Vol. 43, No. 3Acid-base equilibrium: The best clinical approach☆Colombian Journal of Anesthesiology, Vol. 43, No. 3Comprehensive Formulation of Titration Curves for Complex Acid-Base Systems and Its Analytical ImplicationsCritical Reviews in Analytical Chemistry, Vol. 41, No. 2Generalising programming by demonstration More from this issue > Volume 298Issue 2February 2010Pages F471-F471 Copyright & PermissionsCopyright © 2010 the American Physiological Societyhttps://doi.org/10.1152/ajprenal.00240.2009PubMed20103811History Published online 1 February 2010 Published in print 1 February 2010 Metrics
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