Carbon Paste as an Electrode Material - Electroanalysis with Carbon Paste Electrodes - page 63

occur.in.a.small.thickness.of.“bulk”.paste.located.at.the.electrode.surface.(which.is.often.the.case.
for.chemically.modiied.CPEs,.which.are.described.in.detail.in.Chapter.4).

3.4.1 i nTeraCTions aT The C arbon p asTe s urFaCe
Several.electrolytic.and.nonelectrolytic.phenomena.can.occur.at.the.CPE.surface,.and.most.common.
examples.are.presented.as.follows.

3.4.1.1 Electrode Reactions with Charge Transfer (Electrolytic Processes)
As.with.other.electrodes,.straightforward.processes.likely.to.occur.at.a.biased.CPE.surface.are.oxi-
dation.and.reduction.transformations.(Equation.3.3,.[3,658])..They.may.involve.charge.transfers.at.
both.inorganic.and.organic.substances.as.well.as.organometallic.species:

[Ox] + ⇔ ne

−

[ Red ] . (3.3)

.

These.reactions,.and.especially. the rate of charge transfer processes ,.are.affected.by.the.state.of.the.
CPE.surface.and.therefore.by.the.type.of.carbon.used.to.prepare.the.electrode..As.already.discussed.
in.Chapter.2,.graphite.is.the.most.widely.used.carbon.source,.but.CPEs.can.also.be.prepared.using.
other.carbonaceous.materials.such.as,.for.example,.activated.carbon.[632],.glassy.carbon.powder.
[392,659],.carbon.nanoibers.[121,660],.fullerenes.[117,200],.ordered.mesoporous.carbon.[119],.and.
a. wide. range. of. carbon. nanotubes. [661].. The. chemical. state. of. the. surface. of. such. carbon-based.
materials.(i.e.,.presence.of.surface.functional.groups,.which.can.be.tuned.by.appropriate.treatments.
[632]).has.great.inluence.on.the.electrochemical.properties.of.the.resulting.electrodes.in.terms.of.
variable.overpotentials.for.the.detection.of.redox-active.analytes.
After.a.debut.report.[360],. carbon nanotube carbon paste electrodes .( CNTPEs ).have.generated.
a.huge.amount.of.work.because.of.the.extremely.attractive.properties.of.carbon.nanotubes.that.are.
particularly. useful. to. improve. the. performance. of. electroanalytical. devices. [662].. Compared. with.
the.“classical”.CPEs,.CNTPEs.usually.exhibit.faster.charge.transfer.kinetics.and.higher.sensitivities.
([362,363,366,379,398,399];.for.other.details,.see.Section.2.2.3.2)..Even.more.recent,.and.of.comparable.
interest,.are. carbon ionic liquid electrodes .( CILEs ).consisting.of.homogeneous.mixtures.of.graphite.
particles.with.room-temperature.ionic.liquids.acting.as.the.active.binder.[126,451,663];.combinations.
of.ionic.liquids.with.carbon.nanotubes.are.also.feasible.[417,418]..In.brief,.CILEs.offer.higher.sensi-
tivity,.faster.electron.transfer,.and.better.reversibility.than.ordinary.CPEs.[126,456,459,461,474,495,.
663-665].due.to.the.attractive.properties.of.the.room-temperature.ionic.liquids,.such.as.the.increased.
ionic.conductivity,.lower.resistance,.enhanced.ion-exchange.capacity,.or.inherent.catalytic.properties..
(For.example,.the.rate.constant.for.oxidation.of.hydroquinone,.H 2 Q,.was.reported.to.follow.the.order.
“CILE.>.IL.>.CMCPE.>.CPE”.[465,480]..Again,.more.information.is.given.in.Section.2.2.3.3.)
Electron. transfer. reactions. are. also. likely. to. occur. when. using. CPEs. coated. with. polymeric.
membranes. [666-668]. or. preplated. metallic. ilms. [103,617,621,637,669-672].. If. such. metal. ilm-
coated.CPEs.are.combined.with.electrochemical.stripping.analysis,.the.electrode.process.involves.
the.deposition.and.subsequent.dissolution.of.intermetallic.compounds.such.as.Me(Hg) X .amalgams.
[255]. or. Hg-Au. and. Me-Bi. adducts. (expected. to. be. formed. at. gold-. and. bismuth-plated. CPEs.
[260,673])..If.metal.ilms.are.generated. in situ, .these.processes.can.also.be.accompanied.by.addi-
tional.effects.as.a.consequence.of.mutual.competition.between.the.corresponding.ilm.and.the.bare.
carbon.paste.surface.[260].

3.4.1.2 Adsorption and Related Electrode Reactions of Nonelectrolytic Character
Several. redox-active. analytes. can. be. accumulated. by. adsorption. (or. related. nonelectrolytic. phe-
nomena).onto.CPE.surfaces.before.their.electrochemical.detection..This.has.resulted.in.the.devel-
opment.of. adsorptive stripping voltammetry .( AdSV ).as.a.particular.variant.of.the.electrochemical.