Lecture 24,25. Potentiometry Pt2

Lecture 24,25. Potentiometry Pt2 - Glass Glass pH Electrode...

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Unformatted text preview: Glass Glass pH Electrode Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. Membrane Potential Membrane E glass a H + ,sample 2.303 RT = constant + log F a H + ,inside Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman Combination Electrodes Combination Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman Why should the pH glass combination electrode not be stored in pure water? electrode Calibration: Temperature Dependent! Calibration: Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. Calibration Calibration Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. Sources of Error in pH Measurements Sources • Standards Standards • Junction Potential Junction • Junction Potential Drift Junction • Sodium Error (alkaline error) Sodium • Acid Error Acid • Equilibration Time Equilibration • Hydration Hydration • Temperature Temperature Absolute pH ±0.02 Absolute ±0.02 Relative pH ±0.002 Relative ±0.002 Alkaline Error Alkaline Alkaline error of electrodes based on Alkaline different pH glasses. different Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. ed., (Note that this is an example of a pH glass (Note with a particularly poor selectivity.) with Daniel C. Harris, Exploring Chemical Daniel Analysis, 4th ed., W.H. Freeman and Analysis, Company, New York, 2009. Company, Acid Error Acid Gary D. Christian, Analytical Chemistry, 6th ed., John Wiley & Sons, Inc., U.S.A., 2004. Solid-State Ion-Selective Electrodes Solid-State Fluoride Electrode Fluoride: 2.303RT E=k+ log aF - ,sample zF- F Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman Calibration Curves Curves 2.303RT E=k+ log aF - ,sample zF- F Daniel C. Harris, Exploring Chemical Analysis, 2nd ed., W.H. Freeman and Company, New York, 2001. Freeman Solid-State Ion-Selective Electrodes Solid-State Daniel C. Harris, Exploring Chemical Analysis, 3rd ed., W.H. Freeman and Company, New York, 2005. Freeman “Liquid” Based Ion-Selective Electrodes Daniel C. Harris, Exploring Chemical Analysis, 3rd ed., W.H. Freeman and Company, New York, 2005. Freeman “Liquid” Based Ion-Selective Electrodes Counter Ion Ionophore (Valinomycin) Daniel C. Harris, Exploring Chemical Analysis, 3rd ed., W.H. Freeman and Company, New York, 2005. Freeman Ionophores for Ion­Selective Electrodes Ionophores for Ion­Selective Electrodes An ideal reference electrode should E. Bakker et al., Electroanalysis 1998, 11, 915. Ionophores for Ion­Selective Electrodes Ionophores for Ion­Selective Electrodes E. Bakker et al., Electroanalysis 1998, 11, 915. Ionophore Design Ionophore Design P. Buhlmann et al., Chem. Rev. 1998, 98, 1593. Ionophores Forming Covalent Bonds Ionophores Forming Covalent Bonds E. Bakker et al., Chem. Rev. 1997, 97, 3083. An ideal reference electrode should An ideal reference electrode should Ionophore­Based Ion­Selective Electrodes Ionophore­Based Ion­Selective Electrodes An ideal reference electrode should P. Buhlmann et al., Chem. Rev. 1998, 98, 1593. Selectivity Coefficient Selectivity K A,X response to X = response to A A: Analyte X: Interferent :-( :'( æ2.303RT ö z /z E=E +ç log( aA + K A,X aX A X ) ÷ è z AF ø o Example: A Ca2+ ion-selective electrode has a selectivity Example: Ca coefficient KCa2+,Mg2+ = 0.01. What will the change in electrode coefficient potential be when 1 mM Mg2+ is added to 0.1 mM Ca2+? potential ...
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This note was uploaded on 04/06/2011 for the course CHEM 2011 taught by Professor Buhlman during the Spring '10 term at Minnesota.

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