Carbon Pastes and Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 12

numerous. effects. and. side. effects,. making. the. role. of. pasting. liquids. as. important. as. that. of.
the.carbon.(graphite).material.itself..Thus,.one.has.to.pay.comparable.attention.to.the.choice.of.
both.main.constituents.of.carbon.pastes.

2.1.2 C arbon p oWder /g raphiTe
2.1.2.1 Spectroscopic (Spectral) Graphite
A.great.majority.of.binary.(unmodiied).carbon.pastes.are.prepared.from.commercially.available.
graphite.powders..Usually,.they.are.produced.as.conductive.substrates.for.spectroscopy.and.in.this.
way.declared.in.annual.catalogues.of.renowned.companies.and.globally.operating.dealers.with.ine.
chemicals. and. laboratory. equipment,. such. as. Merck ,. Sigma ,. Aldrich ,. Fluka ,. or. Riedel-de-Haen ..
Relatively. frequent. are. also. local. products. from. specialized. manufacturers. marketed. under. the.
respective. trademarks. and. abbreviations.. Here,. for. example,. one. can. quote. the. products. denoted.
by.“CR”.(Czech.Republic),.“RW”.(Germany,.Austria),.“BDH”.(Scandinavia.and.United.Kingdom),.
“SMMC”.(China),.“Acheson,”.“UCP,”.“GP,”.and.“SP”.(United.States),.the.irst.two.named.being.
popular.during.the.early.era.of.CPEs.(for.further.details,.see.Adams's.reports.[2,3,8,9]).
All.the.aforementioned.graphite.powders.usually.offer.the.features.that.must.be.considered.when.
selecting. the. proper. carbon. material. for. making. of. carbon. pastes.. Among. them,. the. following.
criteria.should.be.highlighted:

i. Particle (grain) size and distribution .. Typically,. particle. size. of. common. spectroscopic.
graphites. ranges. in. micrometers. or. in. tens. of. micrometers,. respectively,. when. most. of.
manufacturers.are.able.to.provide.an.oficial.certiicate.with.the.speciication.of.the.overall.
particle.size.distribution.(see,.e.g.,.[171]).

. . . Otherwise,. relatively. reliable. information. about. the. average. distribution. can. also. be.

obtained.on.one's.own.with.the.aid.of.microscopic.imaging..Based.on.empirical.experience,.
it.is.better.if.the.distribution.is.not.very.diverse.and.the.grain.size.of.pulverized.graphites.
is.as.uniform.as.possible..Regarding.standard.spectral.powders,.their.particle.distribution.is.
satisfactorily.uniform,.typically.ranging.within.5-20.μm,.which.is.also.documented.by.the.
bar. diagram. or. in. a. table. inside. the. review. [69],. quoting. for. some. individual. products. of.
the.aforementioned.graphites.the.following.average.mesh:.“CR-5”:.5.μm,.“RW-B”:.5-10.μm,.
“Acheson.G(P)-38”:.10-20.μm,.“UCP-1-M”:.1.μm,.and.“Graphon.GP”:.25.μm.

. . . Naturally,. carbon. powders. used. for. preparation. of. carbon. pastes. are. of. interest. with.

respect. to. their. microstructure. (see. [96,172,173]. and. references. therein).. Spectroscopic.
graphites.do.not.exhibit.any.characteristic.structure.or.pattern.and.their.typical.morphol-
ogy.can.be.approximated.as.a.tangle.of.geometrically.irregular.objects.with.sharp.edges.
and.rather.scratched.surface—see.Figure.2.1.

. . . Besides. ordinary. micrometer-sized. carbons,. there. have. been. reports. on. some. carbon.

paste.mixtures.containing.graphite.with.a.particle.size.of.about.100.nm.[174].or.even.30.nm.
[120]..Such.a.ine.material.can.nowadays.be.purchased.but.is.also.obtainable.in.laboratory.
by.intimately.grinding.some.of.suitable.carbon.powders.in.a.minimill.[174].

. ii.. Low adsorption capabilities .. In. some. cases,. only. appropriate. experiments. reveal. that. a.

graphite.powder.intended.to.be.used.for.preparation.of.carbon.paste.exhibits.a.high.adsorp-
tion. activity. [175,176].. This. undesirable. feature. can. be. identiied. via. the. enhanced. con-
tent.of.oxygen.entrapped.in.pores.of.graphite.or.absorbed.additionally.during.mechanical.
homogenization.of.the.paste.

. . . When.using.CPEs.made.of.such.graphite.powders.in.faradic.(current-connected).mea-

surements,.higher.concentrations.of.oxygen.are.then.registered.as.a.noticeable.plateau-like.
response.(resembling.the.increased.background.within.the.potentials.from.−0.2.to.−0.6.V.
vs..Ag/AgCl).during.the.cathodic.scanning.[2,175].