Carbon Pastes and Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 14

(iii) colloidal. graphite. (hexagonal. carbon. with. extremely. ine. lakes. and. enhanced. conductivity),.
both.having.been.presented.as.the.constituents.of.new.“homemade”.carbon.paste.mixtures.and.used.
in.CPEs.for.pharmaceutical.analysis.
In.the.early.2000s,.Stefan-van.Staden.has.published.her.irst.contribution.on.the.use.of.(iv).diamond.
[118],.represented.by.both.natural.and.synthetic.forms.of.diamond.and.applied.as.ine.powders.with.parti-
cle.diameter.from.1.to.50.μm..The.initial.report.was.soon.followed.by.a.series.of.further.reports,.suggest-
ing.a.versatile.applicability.of.this.quite.surprisingly.chosen.carbon.moiety.(see.later,.in.Section.2.2.3.1).
Also,.there.have.been.some.single.attempts.with.other.carbonaceous.materials.that.are.known.rather.
from.the.industry.and.common.life.than.as.the.product.of.ine.chemistry..At.irst,.it.is.(v).soot.formed.by.
incomplete.combustion.of.hydrocarbons.or,.generally,.from.lammable.materials.of.organic.origin,.men-
tioned.already.by.Adams.[2].and,.after.collecting.a.small.amount.of.this.black.material.inside.a.chimney,.
examined.also.in.carbon.pastes.[188]..(This.study.made.more.or.less.in.an.intention.“just.to.see”.gave.the.
anticipated.result:.the.tested.mixture.had.been.totally.inapplicable.due.to.a.very.high.background.[189].)
Similar.carbonaceous.material.is.also.(vi).activated.charcoal,.widely.used.either.for.medicinal.
purposes.(against.latulence,.for.its.capability.of.absorbing.gaseous.by-products.formed.in.diges-
tion.tract).or.in.the.ilters.of.gas.masks..Also.in.this.case,.one.cannot.expect.excellent.properties.of.
the.respective.carbon.paste.due.to.an.extreme.adsorptibility,.as.well.as.insuficient.purity,.which.
is,.of.course,.the.case.of.formerly.mentioned.soot..Despite.this,.a.commercially.available.activated.
charcoal.(“USP”.powder.[190]).was.once.reported.as.the.material.of.choice.for.a.CPE.that.could.be.
successfully.employed.for.the.quantitative.determination.in.clinical.analysis.
Finally,.when.considering.also.(vii).coal.(“black.coal”),.this.most.common.form.of.natural.carbon.
has.so.far.been.used.as.the.modiier.of.an.ordinary.carbon.paste.[191]..And,.to.complete.the.list.of.
naturally.occurring.carbons,.there.is.also.lignite.(“brown.coal”).whose.use.in.a.CPE.coniguration.
has.never.been.reported,.however.
2.1.2.3 New Forms of Carbon
Most.of.physicochemical.properties—primarily,.distinct.catalytic.capabilities—of.such.materials.
are.due.to.a.speciic.microstructure,.which.is.also.very.characteristic.for.each.of.these.carbons..This.
is.illustrated.by.Figure.2.2,.presenting.microscopic.images.of.three.typical.representatives,.the.irst.
one.in.two.different.variants.
One.of.the.irst.representatives.of.a.material.that.can.be.called.a.new.form.of.carbon.is.apparently.
(i).glassy.carbon.(GC).powder,.having.for.the.irst.time.been.tested.in.the.mid-1990s.[96,192].and,.
later,.successfully.used.in.various.glassy.carbon.paste.electrode.(GCPE).conigurations.(see,.e.g.,.
[95,113,114,193-197]),.including.chemically.and.biologically.modiied.variants.[193,194,196,197]..
The.GC.powder.is.a.specially.treated.graphite.with.spherical.particles.produced.by.pyrolytic.deg-
radation.of.highly.molecular.resins.[184],.when.the.respective.forms.may.differ.from.each.other.in.
the.inal.surface.treatment,.which.is.the.case.of.two.GC.powders.“Sigradur.K”.and.“Sigradur.G”.
(see.again.Figure.2.2,.images.“A”.and.“B”).
Note: . The.reports.on.GC.powders.have.emphasized—besides.their.unique.microstructure—some.
attractive. characteristics. like. minimal. adsorption. or. excellent. polarization. capabilities. despite.
somewhat.“muddy”.consistence.of.some.GCPE.mixtures.[189],.making.their.illing.into.the.CPE.
bodies.with.a.narrower.cavity.quite.dificult.[192]..A.particularly.notable.feature.of.the.GC.pow-
ders.and.of.the.resultant.pastes.is.the.already.mentioned.resistivity.against.“aggressive”.organic.
solvents. used. alone. or. in. mixtures. with. aqueous. solutions. in. the. supporting. media. or. mobile.
phases.for.analyses.by.LC-EC..This.phenomenon.whose.physicochemical.background.is.not.still.
fully.explained.has.been.conirmed.in.many.experiments.with. Sigradur .powders,.when.it.is.evident.
that.the.effective.protection.comes.from.the.graphite.alone..Therefore,.some.newer.interpretations.
explain.this.phenomenon.via.a.relatively.stable.interphase.formed.in.between.the.spherical.carbon.
particles.partially.solvated.by.mobile.phase.[114].or.by.the.beneit.of.the.surface.treatment.of.the.
individual.particles.and.their.repelling.effect.toward.the.molecules.of.an.organic.solvent.[84].