Types Of Titrations; Titrations According To The Measurement Method - Hanna Instruments Hi934 Bedienungsanleitung

2. TYPES OF TITRATIONS

2.1. TITRATIONS ACCORDING TO THE MEASUREMENT METHOD

2.1.1. AMPEROMETRIC TITRATIONS
An amperometric titration is performed by placing two electrodes (often a metal ion selective electrode and a reference
electrode) into the sample solution and keeping the potential of the metal electrode at a selected voltage. The current
that flows, due to the oxidation or reduction of a reactant or product, is plotted vs. volume of titrant to provide the
titration curve and locate the equivalence point. Changes in the current are due to changes in the concentration of a
particular species (being oxidized or reduced at the electrode).
Generally the reaction between the analyte and titrant forms a new species. Depending on the titration, the reactants
are electroactive and the products are not, or vice-versa. Amperometric titration curves look like two straight lines
intersecting at the equivalence point, this is due to the change in the electroactivity of the solution.
Many metal ions can be amperometrically titrated using a precipitation, complexation or redox reaction. Some metal ions
and species that can be determined in this manner include silver, barium, halides, potassium, magnesium, palladium,
molybdate, sulfate, tungstate, zinc, bismuth, cadmium, fluoride, indium, thallium, iodine, and gold.
Figure 1 shows four amperometric titrations and their endpoints. In graph A, the analyte is electroactive and gives
current but the reacted species does not. In B, the reactant is not active but the titrant is. In C, both the analyte and
titrant are active and both give current flow. Graph D, shows the same situation as B; however, the current has an
opposite sign (the titrant is reduced).
2.1.2. POTENTIOMETRIC TITRATIONS
Potentiometric titrations are done by measuring the voltage across the solution using an electrode system. An electrode
system consists of an indicator electrode and a reference electrode. As titrant is added, the variations in the potential
of the indicator electrode, with respect to the reference electrode, are monitored to show the progress of the titration.
Potentiometry is the measurement of a potential under conditions of zero current flow. The measured potential can then
be used to determine the analytical quantity of interest, generally a component concentration of the analyte solution.
Figure 1
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