Quant_Lect_10_Pot - Potentiometry I Current = 0 Nernst...

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Unformatted text preview: Potentiometry I. Current = 0; Nernst equation describes potential/concentration relationship II. Conventional wisdom (1820 - 1995): micromolar detection limit; molar maximum implying 6 order of magnitude dynamic range. Work of Erno Pretsch, Erik Bakker, and co-workers since 1995 has extended range to 9 orders of magnitude. III. Common reference electrodes: Saturated Calomel, Normal Calomel, Silver/Silver Chloride, Silver/Silver Sulfate, Quinone/Hydroquinone, Standard Hydrogen Electrode IV. Type I sensing: measures [M m+ ]/[M n+ ], n≠m. Electrode is passive (typically Pt) V. Type II sensing measures [M n+ ] with metallic electrode M. Also useful for indirect detection of ions that complex with M n+. VI. Type III sensing uses liquid membrane or porous membrane with selective adsorption of analyte on membrane/solution junction. Glass electrode (pH). LaF 3 F- sensor. Macrocycles for ionic sensing. Usually needs reference solution inside electrode to stabilize potential on inside of membrane. Effect of cross-membrane reference solution inside electrode to stabilize potential on inside of membrane....
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