Electroanalysis with Carbon Paste–Based Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 171

W R W C

1 2 3 4

Reagent

Analyte Water Electrolyte

Analytical
cell

Washing
cell

Electrochemical
cell

Regeneration
cell

FIGURE 8.1 Schematic.illustration.of.the.four.successive.steps.usually.involved.in.a.typical.voltammetric.
analysis.performed.at.a.chemically.modiied.carbon.paste.electrodes.after.accumulation..W,.R,.and.C.refer.to.
the.working,.the.reference,.and.the.counter.electrodes,.respectively..➊.open-circuit.accumulation;.➋.rinsing;.
➌.electrochemical.detection;.➍.chemical.regeneration.

Up.until.now,.more.than.70.chemical.elements.across.the.whole.periodic.table.were.of.interest.
[7,83]. and. determined. via. the. corresponding. single. ions,. complexes,. and. molecules. when. using.
various.CPEs,.CMCPEs,.and.CP-biosensors.in.combination.with.voltammetric,.amperometric,.or.
potentiometric.techniques.
Typically,.the.data.presented.in.tables.concern.the.sensing.(practical).applications,.while.omit-
ting.investigations.in.which.the.inorganic.analytes.had.served.as.model.systems.for.testing.some.
new.devices.or.elaborating.novel.methodologies..Special.attention.was.given.to.quantitative.deter-
minations.and.much.less.to.qualitative.aspects.(e.g.,.demonstrating.a.catalytic.effect,.characterizing.
a.new.material.as.electrode.modiier,.etc.);.some.of.the.latter.is.presented.in.Section.4.3.
In. inorganic. analysis,. the. methods. for. quantiication. have. predominantly. employed. various.
CMCPEs,.allowing.one.to.increase.both.sensitivity.and.selectivity.of.the.respective.method(s).by.
means. of. a. special. preconcentration. step.. Usually,.it. is. an. integral. part. of. the. respective. electro-
chemical.stripping.method,.involving.the.chemical.accumulation.of.the.target.analyte.by.a.suitable.
electrode.modiier—see.general.operational.scheme.in.Figure.8.1.
After. such. accumulation,. the. electrochemical. detection. can. be. accomplished. by. directly.
reducing.the.preconcentrated.species,.but.the.“electrolytic.deposition/anodic.reoxidation”.scheme.
is. often. preferred. due. to. the. generally. poorer. pathways. for. cathodic. reductions. suffering. from.
the.undesirable.interferences.from.molecular.oxygen.contained.in.the.paste..In.some.cases,.the.
preconcentration. and. the. detection. step. can. also. be. performed. in. different. solutions,. when. the.
sample. solution. acts. in. the. irst. phase. for. depositing. the. analyte. either. as. such. or. in. a. form. of.
suitable. compound,. whereas. the. proper. stripping/detection. takes. place. in. a. new. medium—the.
so-called. “blank”—being. free. and. protected. from. the. original. matrix. constituents. and. other.
unwanted.residua.
And.if.needed,.a.special.rinsing.solution.can.also.be.added.between.the.two.main.steps..Both.
these.variants.are.known.as.“medium.exchange”.(MEx.[55];.see.also.Section.6.2.2).which.is.quite.
a.popular.approach.in.inorganic.electrochemistry,.and.much.more.frequent.and.almost.obligate.in.
pharmaceutical.and.clinical.analysis,.operating.in.particularly.complex.matrices.of.biological.luids,.
which.is.reviewed.in.Section.8.3.

8.1.1 n oble M eTals
Au III ,.Ag I ,.Hg II .(or.even.Hg 2 II ,.resp.),.and.Cu II .species.in.aqueous.solutions.of.deinite.composition.
(inducing.selected.speciation.to.the.element).can.be.electroactive.at.CPEs.(Au III .mainly.as.AuCl 4 − ;.