eDAQ Picostat, Руководство пользователя

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Chapter 5 — Techniques 83
If the solution is being stirred during the procedure then eventually all
the substrate can be oxidized, or reduced, to a new material and the
technique may be referred to as electrosynthesis rather than
chronoamperometry.
If the reaction causes the formation of a polymer film on the electrode
(for example pyrrole to polypyrrole, or aniline to polyaniline) then the
technique may be referred to as electropolymerisation.
To effect the electrolysis of a substrate a potential should be chosen
which is at least 50 – 200 mV more oxidising (or reducing) than the
half-wave potential in order to ensure complete reaction. It is usually
important to separate the auxiliary (counter) electrode from the main
body of the electrochemical cell by means of a salt bridge. This is to
prevent the reduction products formed in the region of the auxiliary
electrode reacting with the products of oxidation at the working
electrode (or, if reducing the substrate, to prevent the products of
oxidation forming around the auxiliary electrode from reacting with the
reduction products at the working electrode). The working electrode is
usually constructed to have relatively large surface area so that a
greater amount of material can be electrolyzed in a small time — thus a
plate or gauze electrode is usually chosen, although reticulated vitreous
carbon (RVC) which has an open pore foam structure, is also a popular
choice.
The conversion of large amounts of substrate (> 100 mg) in reasonable
times requires relatively high currents to be passed through the cell.
Thus the Potentiostat (maximum current 100 mA) is usually more
suitable than the Picostat (< 100 nA) or QuadStat (< 1 mA/channel) for
electrosynthesis. The production of organic compounds in highly
resistive non-aqueous solvents often requires the addition of large
amounts of electrolyte to sustain the current flow (and which can lead to
difficulties in later separation of the product). For studies using water, or
other protic solvent, the addition of a small quantity of acid (or base)
can greatly increase the conductivity of the solution, without having to
add large amounts of electrolyte.
Controlled Current Electrolysis
These techniques are essentially the same as Chronopotentiometry,
page 77 , and require the use of a galvanostat. The Potentiostat, when