Chemistry Reference
In-Depth Information
charges,.the.corresponding.conversion.factors.(e.g.,.
f
i
→
c
.from.voltammetric.current.to.surface.con-
centration).are.not.eliminated,.when.replacing.the.concentrations.by.the.signals.(Equation.4.18):
2
K
′′
=
i
/(
i
−
i
) /(4
*
f
*
[ ]
A
)
.
(4.18)
A,eq
A,max
A,eq
i
→
c
sol
.
In.this.respect,.
K
″.has.a.direct.meaning.only.when.comparing.the.same.or.similar.systems.with.
voltammetric.measurements.and.is.not.directly.comparable.to.formation.constants.as.given.in.the.
literature,.because.surface.concentrations.are.involved.rather.than.volume.concentrations..For.the.
determination.of.
f
i
→
c
,.coulometric.measurements.with.the.same.sensors.are.indispensable.because.
they.provide.the.necessary.relation.between.the.surface.concentration.and.the.voltammetric.signal..
Additionally,.the.value.for.
K
″.cannot.be.obtained.as.simply.as.in.the.1:1.case,.but.it.has.to.be.estimated.
by.corresponding.its.[1080].
The.dependence.of.the.voltammetric.current.on.the.accumulation.or.reaction.time.(see.Figure.
4.17B).is.mathematically.shown.in.Equation.4.20,.which.is.in.fact.rather.different.to.Equation.4.12.
but.is.similar.in.shape.to.the.previous.graph.(once.again,.compare.both.parts.of.the.igure):
1
.
(4.19)
i
=
i
∗
1
-
A t
,
A eq
,
(
4
∗
f
∗
i
∗
k
∗ ∗
t A
[
]
+
1
)
i
→
c
A eq
,
v
sol
.
The.proper.application.of.this.procedure.then.allows.one.to.estimate.the.thickness.of.the.sorp-
tion.layer.using.the.formula.of.Equation.4.14,.which.can.be.formally.rewritten.as.follows.(as.
Equation.4.20):
−
1
J
= [
AM
]
*
([
AM
]
*
r
*
m
)
.
(4.20)
max
surf,max
M
.
when.the.individual.variables.and.symbols.are.otherwise.identical.
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