Carbon Pastes and Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 45

carbon.nanomaterial.used.[120],.the.microelectrodes.themselves.devised.with.a.special.
piston.mechanism.for.extruding.the.ine.paste.from.tiny.glass.capillaries.(with.ID.from.
5.to.50.μm).
(III) Carbon paste ultramicroelectrodes (CP-UMEs) .. Similarly. like. CPμEs,. also. ensembles.
of. these. especially. miniature. electrodes. had. shortly. attracted. electrochemists'. attention.
in. the. late. 1980s. as. documented. in. three. interesting. reports. [174,613,614].. Within. these.
investigations,.it.was.hoped.that.CP-UMEs.would.further.improve.some.physicochemical.
and.electrochemical.characteristics.of.the.already.existing.ensembles.of.UMEs.and.such.
superiority.was.thanks.to.unique.mechanical.properties.of.heterogeneous.carbon.pastes.
In.this.respect,.some.anticipations.have.been.fulilled.(e.g.,.those.speculating.on.a.lesser.ohmic.
resistance.or.enhanced.capacitance),.some.predictions.mostly.failed.(e.g.,.more.favorable.reaction.
kinetics.compared.to.the.macroelectrode.arrangements).
Figure. 2.13. and. Scheme. “C”. depict. how. to. accomplish. and. prepare. ensembles. of. CP-UMEs..
According. to. the. authors. of. this. assembly. [613],. it. was. necessary. to. use. a. special. carbon. paste.
(CP).made.of.very.inely.grinded.graphite.with.particles.of.ca..100.nm..(The.resultant.powder.was.
a.nanocarbon.at.that.time,.when.similar.materials.had.not.been.yet.called.with.the.modish.“nano”.
preix.[8].).The.respective.and.very.elastic.paste-like.mass.was.then.thoroughly.pressed.into.a.poly-
meric.membrane.(3).with.micrometric.pores.(M;.see.also.cross.section)..After.careful.removal.of.
the.exceeding.paste,.the.illed.membrane.was.stretched.over.the.tip.of.an.electrode.body.(1).and.
ixed.irmly.with.a.rubber.ring.(4)..The.supporting.electrode.area.was.the.GC.disc.(2).serving.as.a.
contact.site,.collecting.the.signal.from.all.the.individual.carbon.paste.ultramicrodiscs.isolated.inside.
the. membrane. pores.. As.shown. for. a. similar.arrangement. of. CP-UMEs. [174,614],. also.“normal”.
CPE.could.properly.serve.as.the.collector.
Note: . Although. ensembles. of. CP-UMEs. had. made. more. or. less. an. ephemeral. appearance,.
they.contributed.to.the.understanding.of.some.processes.associated.with.the.behavior.of.carbon.
paste-based. electrodes.. Namely,. the. studies. with. CP-UMEs. helped. to. deine. the. character. of.
the.standard.carbon.paste.(macro).surface.being.classiied,.at.that.time,.to.be.rather.an.array.of.
microelectrodes.than.a.uniform.area.of.a.pool.electrode.[276]..When.using.cyclic.voltammetry,.it.
was.demonstrated.that.whereas.common.CPE.coniguration.had.exhibited.typical.voltammograms.
with.normal.peaks,.ensembles.of.CP-UMEs.gave.rise.to.sharp.sigmoidal.curves..Hence,.the.latter.
indirectly.conirmed.that.miniature.regions.of.carbon.paste.had.been.separated.mechanically.in.
the.pores,.obeying.the.fundamental.criterion.of.each.microelectrode.to.have.comparable.dimen-
sions.of.the.diffusion.layer.and.of.the.electrode.surface.beneath..In.contrast.to.this.and.according.
to.latest.interpretations.[83],.the.surface.of.ordinary.CPE.can.now.be.imaged.via.a.model,.where.
the.individual.electrode.miniregions.formed.by.binder-coated.graphite.particles.are.merging.into.
a. uniform. area. and. the. corresponding. diffusion. layers. are. completely. overlapped.. The. result. is.
then.a.behavior.known.for.traditional.solid.electrodes,.including.well-developed.peaks.in.cyclic.
voltammograms.
A.decade.ago,.ensembles.of.CP-UMEs.had.surfaced.once.more.[615].in.two.different.conigu-
rations. of. a. (i). CP-disc. shaped. electrode. (with. overall. diameter,.∅ CP . =. 100-150.μm),. and. a. (ii).
CP-band.electrode,.both.exhibiting.characteristic.properties.of.microelectrodes.but.suffering.from.
rather.poor.reproducibility.(of.about.±20%).
2.3.7 s peCial C onsTruCTions oF Cpe s
In.this.closing.section,.three.unique.constructions.of.carbon.paste-based.electrodes.are.presented.as.
very.atypical.conigurations.standing.beyond.any.established.classiication..The.irst.one.has.been.
reported.as.carbon.paste.“U”-shaped.electrode.[616].illed.with.mercury.and.having.one.end.loaded.
with. carbon. paste. linked. to. the. Hg-reservoir. through. a. solid. carbon. insert.. Due. to. the. presence.