Chemistry Reference
In-Depth Information
the.OMCPE.was.also.recommended.anodic.stripping.voltammetry.of.heavy.metal.ions,.offering.a.
superior.sensitivity.compared.to.common.CPEs.
Finally,.the.late.2000s.witnessed.the.use.of.the.remaining.carbon.nanomaterials..Firstly,.they.
arrived. in. the. form. of. (viii). carbon. nanoparticles. (of. about. 30.nm. in. diameter. [120]). in. a. carbon.
paste.microelectrode.(nCμPE).that,.like.in.previous.cases,.underwent.more.or.less.routine.character-
ization.with.model.redox.systems.of.both.inorganic.and.organic.nature..The.survey.continues.with.
(ix).carbon.nanoibers.(CNF;.[121,128,139,202,203];.see.Figure.2.2,.image.“C”),.obtainable.either.
by.machine-controlled.growth.during.electrospinning.or.with.the.aid.of.chemical.vapor.deposition.
(CVD),.and.with.(x).graphene.(GR;.[204])..The.latter.is.another.allotrope.of.carbon,.occurring.in.
one-atom-thick.sheets.with.a.honeycomb-like.structure.and,.in.fact,.represents.the.limiting.case.of.
an.indeinite.polyaromate..To.date,.GR.is.also.the.last.newcomer.from.the.family.of.alternate.car-
bons.being.tested.in.the.carbon.paste.conigurations.
And.the.most.popular.(xi).CNTs.([122];.see.again.Figure.2.2.and.image.“D”).that.can.be.titled.as.
“the.carbon.of.the.new.millennium”.also.in.the.electrochemistry.with.CPEs.[84].are.already.embodied.
in.a.special.group.of.CNT-based.paste.electrodes.[123,124]).requiring.to.be.discussed.in.more.detail.
2.1.3 p
asTing
l
iquid
/b
inder
As.already.emphasized,.mechanical.connection.of.the.individual.carbon.particles.into.a.uniform.
mass.is.not.the.only.role.of.carbon.paste.binders..Each.pasting.liquid,.including.highly.chemically.
inert.substances,.codetermines.principal.physicochemical.and.electrochemical.properties.of.each.
CPE,. including. all. newly. described. types. (see,. e.g.,. [83,84,111]. and. references. therein).. Typical.
parameters.of.a.suitable.pasting.liquid.can.be.summarized.in.a.similar.way.like.for.carbon.materi-
als,.when.pointing.out.the.following.features:
.
i..
Chemical inertness and electroinactivity
..Liquid.binders.used.for.the.preparation.of.car-
bon.pastes.are.highly.stable.substances.and.their.interactions.at.the.electrode.interface.or.
in.the.electrode.bulk,.respectively,.are.usually.of.purely.physical.nature.[3,83]..However,.
some. liquid. binders. may. also. interact. chemically,. for. instance,. via. active. participation.
in.acido-basic.equilibria..This.is.the.case.of.some.organophosphate.esters.as.shown.in.a.
pioneering.study.with.otherwise.electroinactive.and.water-insoluble.liquid.binders.[205],.
forming.voluminous.protonated.cations.with.high.afinity.toward.ion.pairing.
.
. . Electrochemical. inertness. of. the. binder. is. required. in. experiments. based. on. the. cur-
rent. low,. that. is,. in. faradic. measurements. such. as. various. voltammetric. modes. (e.g.,.
[8,9,25,34,41,61]),. amperometry. [62-65],. constant. current. chronopotentiometry. [190],. or.
coulometry. [206].. This. demand. is. not. the. case. of. carbon. paste. electroactive. electrodes.
(CPEEs). (i.e.,. CPEs. with. electrolytic. binder. [38,151]). or. other. CPEs. with. electroactive.
binders. if. such. constituents. do. not. interfere. with. the. analytical. signal. of. interest. [207]..
Electrochemical.activity.is.of.lesser.importance.in.potentiometric.indication.[159],.when.
carbon. paste. mixtures. may. contain. even. highly. reactive. compounds. like. organic. nitro.
esters.such.as.2-nitrophenyl-octyl.ether.(NPOE).(see,.e.g.,.[208].and.references.therein).or.
in.stripping.potentiometry.with.chemical.oxidation.[209,210].
.
ii..
Low volatility
..Apart.from.attitudes.associated.with.direct.physical.contact.with.poten-
tially.harmful.vapors,.the.stability.and.lifetime.of.CPEs.prepared.from.more.volatile.past-
ing.liquids.is.rather.limited..Due.to.slow.evaporation.of.the.binder,.the.respective.carbon.
paste. mixtures. become. desiccated,. which. is. accompanied—besides. visible. changes. in.
consistency—by. irreversible. alterations. of. physicochemical. and. electrochemical. prop-
erties.[83,177]..These.trends.can.be.well.documented.on.CPEs.made.of.liquid.tricresyl.
phosphate.(TCP).that,.despite.their.relatively.high.viscosity,.was.found.to.evaporate.from.
carbon.paste.mixture.during.1.or.2.weeks.only.[205]..Regarding.common.binders,.the.
requirement.of.minimal.volatility.is.obeyed.by.most.of.the.liquids.so.far.proposed.
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