Carbon Paste as an Electrode Material - Electroanalysis with Carbon Paste Electrodes - page 66

implies.the.use.of.an.electrocatalyst,.that.is,.a.catalyst.that.participates.in.an.electrochemical.reac-
tion,.which.modiies.and.increases.the.rate.of.electron.transfer.reactions.without.being.consumed.
in.the.process,.resulting.in.signiicant.improvement.in.the.performance.of.electrochemical.sensors.
[720].. Facilitating. the. electron. transfer. reaction. is. usually. achieved. by. the. appropriate. choice. of.
a. suitable. modiier. that. can. be. either. added. directly. in. the. carbon. paste. mixture. or. adsorbed—
eventually,. chemically. immobilized—at. the. carbon. paste. surface.. The. versatility. of. the. carbon.
paste.matrix.enables.one.to.use.a.wide.range.of.mediators,.from.solid.particles.to.molecular.systems.
(organic.molecules.or.organometallic.complexes),.including.supra.and.macromolecular.compounds..
Several.hundreds.of.electrocatalysts.have.been.used.to.modify.either.the.surface.or.(mostly).the.bulk.
of.CPEs;.they.are.not.mentioned.here.as.they.are.described.in.Section.4.3..In.some.cases,.relatively.
high. electrocatalytic. activity. can. also. be. achieved. through. electrolytic. activation. of. the. unmodi-
ied.(bare).carbon.paste.[600].or,.as.largely.developed.in.recent.years,.by.merely.choosing.a.proper.
carbon.material.(e.g.,.carbon.nanotubes.[123,661].or.ordered.mesoporous.carbons.[119]).or,.alterna-
tively,.by.using.an.active.binder.such.as.room-temperature.ionic.liquids.[456,471].or.a.combination.
of.the.two.approaches.[418].
For.instance,.the.simple.replacement.(even.partial).of.graphite.by.carbon.nanotubes.was.likely.
to.dramatically.enhance.the.sensitivity.of.the.composite.electrode,.as.illustrated.for.the.detection.of.
organic.molecules.[398,389,423,721],.for.direct.electrochemistry.of.redox.proteins.(e.g.,.hemoglobin.
[417,431]),.or.in.biosensors.[722,421]..Imidazolium-.or.alkylpyridinium.hexa-luorophosphate-based.
CILEs.were.reported.to.exhibit.intrinsic.electrocatalytic.properties.in.the.voltammetric.detection.of.
a.long.line.of.organic.molecules.[480,458,466,477,484,493,494,498,500,505,723]..Sometimes,.addi-
tional.electrocatalysts.(e.g.,.polyoxo-metallates.[126,515]).can.be.introduced.into.CILE.to.further.
improve.its.catalytic.behavior.
Interpretations.of.electrocatalytic.phenomena.taking.place.at.the.CPE—and,.in.fact,.the.other.
processes. as. well—are. typically. based. on. empirical. observations. [68],. and. theoretical. formulas.
are.seldom.needed..Nevertheless,.in.association.with. surface characteristics .of.CPEs,.there.have.
been.some.attempts.to.deine.such.models.and.equations.for.calculations..This.is.the.case.of.a.(i).
formula. describing. the. speciic. adsorption. of. some. organic. compounds. at. the. CPE. [24]. or. a. (ii).
relation.for.calculating.the. effective surface area for electrolytic deposition .[724].with.the.aid.of.
the.geometric.parameters.of.graphite.particles.and.the.actual.carbon-to-pasting-liquid.ratio.used..
Since.the.latter.could.be.of.some.interest.today,.in.connection.with.the.boom.of.metallic-ilm-plated.
CPEs.[7,83,84,255,268],.the.respective.equation.can.be.given.here..Thus,.in.somewhat.rearranged.
form,.one.has

2

( d / 2) × (

V V

/ )

p CPE

C

A = 0.97

(3.10)

eff CPE ( )

.

0.14 1.9

[ d × ( V V / ) ]

.

C L C

where
d CPE .is.the.geometric.diameter.of.the.CPE.surface
d C .is.the.average.diameter.of.carbon.particles.(that.must.be.in.an.interval.of.10-90.μm)
( V L / V C ).is.the.(pasting).liquid-to-carbon.(powder).ratio.in.volume.%,.v/v.[724].Otherwise,.some.
more.theoretical.approaches.with.the.mathematical.background.are.occasionally.used.in.mod-
eling.of.test.measurements.with.CMCPEs.and.CP.biosensors;.see.Sections.4.4.and.5.3.

3.4.1.5 Synergistic Processes and Interactions
Some.of.the.aforementioned.processes.are.not.restricted.to.the.CPE.surface.only,.and.the.carbon.paste.
bulk.(interior).may.also.be.involved.in.the.overall.interactions..This.is.the.case.of. extraction —as.one.
of.the.most.typical.processes.taking.place.inside.the.carbon.paste.and.therefore.being.the.subject.of.
special.interest.in.the.following.Section.3.4.2,.where.it.is.shown.that.extractive.processes.can.occur.
in.addition.to.the.afore-mentioned.adsorption,.ion.pairing,.complexation,.or.precipitate.formation.