Carbon Pastes and Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 28

particularly.valid.for.the.latter.two..In.the.late.2000s,.they.both.have.achieved.the.status.of.domi-
nant.groups.among.novel.carbon.paste-based.electrodes,.sensors,.and.detectors..The.following.
sections.bring.mainly.the.basic.characterization.of.all.three.groups,.whereas.the.details.on.proper.
functioning,.ways.of.modiication,.and.practical.applicability.are.only.sketched..Again,.all.this.
information.material.is.gathered.in.Chapters.4.and.5.and,.then,.in.Chapter.8,.where.the.individual.
electroanalytical.methods.are.speciied.by.means.of.typical.data.gathered.in.a.series.of.summa-
rization.tables.
2.2.3.1 Diamond as the Electrode Material and Diamond Paste Electrodes
Besides.natural.and.synthetic.forms.of.hexagonal.graphite,.or.various.new.forms.of.carbon,.there.
is.also.a.cubic.allotrope.of.the.same.element—diamond..Apart.from.other.differences.between.the.
individual.forms.of.carbon,.it.is.well.known.that.the.latter.is.an.excellent.electric.insulator.(with.
resistivity. of. about. 10 20 . Ω.·.cm −1 . [337]).. Thus,. the. pure. forms. of. diamond. were. for. a. long. time.
believed.to.be.inapplicable.in.electrochemical.measurements.
However,.this.hindrance.was.overcome.by.the.appearance.of.synthetically.doped.and.suficiently.
conductive.modiications.that.rapidly.occupied.a.position.in.the.corresponding.electrode.conigura-
tions.[337,338],.especially.those.based.on.boron-doped.diamond.ilms.[339],.conigured.as.a.very.
thin.crystalline.layer.material.immobilized.onto.a.suitable.electrode.supports,.and.giving.rise.to.a.
large.family.of. boron-doped diamond electrodes .( BDDEs ).
If. one. considers. the. diamond,. as. well. as. its. boron-doped. variant,. to. be. an. alternative. to. car-
bon. or. graphite,. respectively,. there. is. yet. another. example. of. such. carbonaceous. material.. It. is.
boron.carbide.(B 4 C,.a. Norbide .product.with.satisfactory.conductivity),.representing—in.a.certain.
context—a.historic.predecessor.of.carbon.pastes.in.Adams's.laboratories.[340,341]..This.crystal-
line.and.extremely.compact.substance,.not.dissimilar.to.diamond,.was.tested.in.the.form.of.a. boron
carbide electrode .( B 4 CE ).in.the.bulk.coniguration,.being.described.as.“a.solid.electrode.inert.to.a.
much.higher.degree.than.do.the.noble.metal.counterparts”.[3]..From.today's.point.of.view,.it.is.quite.
logical.to.speculate.on.why.the.same.material.had.not.been.examined.in.the.powdered.form.and.
as.a.paste,.which.would.have.given.rise.to.a.true.alternative.to.“normal”.carbon.pastes.at.the.time,.
when.they.were.just.coming.to.the.fore..The.answer.can.likely.be.withdrawn.from.Adams's.topic,.
where.he.mentioned.“dificulties.to.mount.the.electrode,”.which.may.imply.comparable.problems.
with.inevitable.grinding.of.this.extraordinarily.hard.material.
However,. the. early. 2000s. had. seen. such. an. attempt. with. pure. diamond,. when. the. resultant.
powders.were.immediately.presented.in.a.form.of.diamond.paste.electrodes.(DPEs;.[118])..Since.
then,.energetic.propagators.of.this.new.type.of.electrodes.have.published.a.full.dozen.contributions.
[342-354]. that. were. to. convince. the. electrochemical. audience. about. realness. of. incorporating.
nondoped.diamonds.into.the.functioning.electrode.assembly.
Reportedly.[118],.the.pastes.containing.either.(i).natural.or.(ii).synthetic.diamond.powder.(both.
available.as.especially.ine.powders.with.average.particle.size.of.1.μm.or.even.rougher.fractions.with.
mesh. of. 50.μm). and. mixed. with. ordinary. POs. typically. exhibit. a. very. high. sensitivity. in. faradic.
measurements,.giving.rise.to.remarkably.high.currents.during.the.detection.of.analytes.at.“com-
mon”.concentrations..Maybe.that.such.high.absolute.values.of.the.overall.signal-to-noise.ratio.could.
be.behind.achieving.some.amazing.LODs.down.to.1.×.10 −12 .mol.·.L −1 .for.the.single.ions.[344,347],.
as.well.as.for.some.analytes.of.organic.and.biological.nature.[345,352].
To.date,.DPEs.have.been.applied.to.the.determination.of.a.series.of.inorganic.ions,.namely,.Fe 2+ .
and. Fe 3+ . [118,347],. Cr 3+ . and. Cr VI . [344,346],. Pb 2+ . [349],. Ag + . [353],. and. iodide,. I − . [342].. Of. inter-
est. were. also. some. biologically. important. compounds. and. pharmaceuticals:. L-. and. D-pipecolic.
acids.[343,350,351],.creatine.and.creatinine.[345,352],. Azidothymidine .([348],.one.of.the.effective.
therapeutic.agents.for.retarding.AIDS.progress),.and. Sildenail citrate .([354],.known.worldwide.as.
Viagra ® . for. treating. man's. erectile. dysfunctions).. In. association. with. the. individual. method. pro-
posed,.it.is.interesting.that.all.the.procedures.with.DPEs.had.employed.solely. two-component dia-
mond pastes .or,.else,.that.there.was.no.adaptation.to.a.chemically.or.biologically.modiied.variant.