Techniques {polarography} can measure solution concentration, by diffusion-controlled oxidation or reduction at electrode surface. Voltage relates to metal-ion concentration.
purposes
Polarography measures transition metal ions, inorganic ions, water and blood oxygen levels, and ion resonance in organic compounds, aldehydes, acids, ketones, nitrogen compounds, and halides. Inorganic ions are sulfide, oxide, hydroxide, and chromate. Polarography is sensitive, with ion concentrations from 0.01 M to 0.000001 M.
process
A small electrode receives potential that depletes ions near it. With no stirring, electrode and solution have a concentration gradient. Polarized electrodes block ion flow, so nearby ion concentration is due only to ion diffusion from solution. Diffusion rate depends on concentration, if concentration gradient is constant. Potassium chloride minimizes electrostatic effects. Impurities and capacitances can cause other currents.
types
In electrodes {dropping mercury electrode} (DME), mercury can oxidize, removing oxygen gas from solution. Dropping mercury electrodes, rotating disk electrodes, or ring-disk electrodes remove surface layer.
Polarography methods {amperometry} can measure oxidation or reduction by titration, instead of directly.
5-Chemistry-Analytical Chemistry-Electricity
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Date Modified: 2022.0225