Chemistry Reference
In-Depth Information
been.structured.as.a.kit,.and.the.overall.scheme.can.be.lexibly.adapted.according.to.one's.require-
ment,.for.instance,.by.adding.new.testing.subprocedure(s).evaluating.the.performance.of.a.particular.
instrumental.technique.(e.g.,.potentiometry,.amperometry,.or.measurements.in.lowing.streams),.on.
the.contrary—also.by.removing.those.assays.and.procedures.that.are.irrelevant.for.a.given.application.
In.order.to.make.the.individual.tests.systematic.and.the.respective.results.comparable,.numerous.
model systems
.have.been.proposed..Among.them,.one.can.recommend.the.following:.
Ag
+
/
0
,.
Fe(CN)
6
3/4−
,.
both.representatives.of.reversible.inorganic.redox.pairs;.
I
2
/I
−
,.essentially.reversible.system.whose.oxi-
dation.form.exhibits.marked.tendencies.to.be.extracted.onto.the.carbon.paste.bulk;.
quinone
.or.
hydro-
quinone
,.typical.“quasi”.reversible.organic.redox.system;.
phenol
,.
phenothiazine
,.fairly.electroactive.
substances.yielding.the.oxidation.products.(or.intermediates).with.strong.adsorption.capabilities;.and.
N
2
H
5
+
,.
ascorbic acid (AA)
,.reduced.forms.of.typically.irreversible.systems.whose.reaction.rate.can.be.
controlled.
by
.electrocatalysis.(i.e.,.suitable.for.testing.of.activation.procedures.and.their.eficiency).
Besides.the.speciication.of.various.properties.and.parameters,.testing.measurements.may.also.
help. in. assessing. the. quality. of. both. main. carbon. paste. constituents. or. the. optimal. carbon. paste.
composition,.here,.through.simultaneous.experiments.with.a.series.of.carbon.pastes.differing.solely.
in.the.carbon-to-pasting-liquid.ratio..Furthermore,.suitably.chosen.procedures.may.also.help.in.
test-
ing the electroanalytical performance
.of.a.CPE.(e.g.,.reproducibility.and.repeatability,.operational.
potential.range.and.the.background.level,.detection.capabilities,.etc.)..A.more.detailed.discussion.
on.the.individual.tests.and.assays.is.beyond.the.scope.of.this.paragraph,.and.the.reader.is.advised.to.
consult.some.special.literature.(see,.e.g.,.[175,176].and.references.therein).
Finally,. the. testing. can. also.be. tailored.for. both.
chemically and biologically modiied carbon
paste electrodes,
. with. special. attention. paid. to. the. quality. and. proper. function. of. the. modify-
ing. substance(s).. Such. measurements. have. already. been. uniied. in. the.
testing and modeling of
CMCPEs/CP biosensors
.as.shown.in.Sections.4.4.and.5.3.
Note:
. In. the. past,. including. the. early. era. of. CPEs,. there. were. some. efforts. made. to. unify. the.
individual.electrodes.via.a.“standardization.of.carbon.pastes.”.Besides.initial.attempts.by.Adams.
himself.(mentioned.in.[68]),.followed.by.other.authors.[40,60],.there.were.also.repeated.attempts.to.
propose.addressed.
extraction quotients
.[20,219,220].to.quantify.speciic.bulk.processes.at.CPEs.for.
the.determination.of.selected.organic.compounds..Especially.the.latter.seems.to.be.a.inely.elabo-
rated.work,.and.it.is.quite.surprising.that.it.has.not.attracted.more.attention.
Recently,. the. term. “standardization”. of. CPEs. has. surfaced. again. in. association. with. our. new.
activities..After.a.preliminary.sketch.of.the.problem.(see.[83].and.pp..302-303.and.317-318.therein),.
our.research.group.inally.attempted.to.elaborate.a.new.study.focused.on.postulating.and.experi-
mental.veriication.of.a.simple.
qualitative parameter
.that.could.objectively.deine.the.behavior.of.
CPEs..One.of.the.respective.measures.was.called.“CPE-index,”.
χ
CPE
,.which.relected.a.simple.two-
step.assay.with.the.ferri.or.ferrocyanide.model.redox.system,.expressed.by.two.alternate.formulas:
∆
∆
E
E
[Fe(CN)
3 4
/
−
−
]
P
6
CPE
=
c
CPE
.
(3.2a)
3 4
/
[Fe(CN)
]
.
P
6
TEOR
∆
∆
E
E
[Fe(CN)
3 4
/
/
−
−
]
P
6
CPE
′
=
c
CPE
.
(3.2b)
3 4
[Fe(CN)
]
.
P
6
GCE
where
Δ
E
P
.=.
E
P
(Ox).−.
E
P
(Red)
Δ
E
P TEOR
.=.59.mV.[657]
Δ
E
P
(
GCE
)
.≥.59.mV
Δ
E
P
(
CPE
)
.≫.59.mV
Search WWH ::
Custom Search