Instrumental Measurements with Carbon Paste Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 146

polarity.and.very.low.intensity.(at.the.μA-level).can.be.set.and.varied.as.required.via.the.software.
of.modern.electrochemical.analyzers.[1983].
In. principle,. CPEs. are. applicable. in. both. PSA. and. CCSA. without. signiicant. limitations..
However,. compared. with. extensive. voltammetric. applications,. CPEs. have. been. combined. with.
stripping.potentiometry.only.occasionally.[13,190,684,1988],.and.some.valuable.properties.of.these.
electrodes.remained.practically.unnoticed..Among.them,.one.can.quote.very.favorable.signal-to-
noise.characteristics.of.CPEs.within.a.wide.anodic.potential.range.utilizable.mainly.for.oxidation.of.
organic.compounds.or.unique.interaction.between.the.carbon.paste.and.an.analyte..As.conirmed.
recently. [254,710,711,1989,1990],. for. example,. extraction. and. ion-pairing. processes. at. CPEs. are.
highly.effective.even.in.the.PSA.
Perspectives.of.CPEs.in.stripping.potentiometry.have.been.discussed.and.some.examples.have.
been.given.for.the.accumulation.of.analytes.using.both.electrolytic.and.nonelectrolytic.deposition.
[210]..CPEs.covered.with.mercury.ilms.are.applicable.for.the.determination.of.gold.and.some.heavy.
metals.[108,209,1992,1993],.whereas.with.gold.ilms.for.the.determination.of.mercury,.copper,.and.
arsenic.[108,209],.the.latter.in.both.As III .and.As V .forms.(see.also.Section.8.1.and.Figure.8.6).
A.decade.ago,.a.novel.approach.to.the.PSA.measurements.was.presented.based.on.total.substitution.
of.mercury.by.bismuth.[626],.and.this.intentional.replacement.had.been.innovative.in.two.respects..
First,.bismuth(III).salts.may.be.applied.for.forming.bismuth.ilms,.and.these.ilms.can.be.generated.
on. such. supports. like. CPEs.. Secondly,. Bi(III). salts. may. substitute. Hg(II). in. its. role. of. an. oxidant..
This.has.offered.new.possibilities.for.determinations.of.trace.heavy.metals.like.Cd,.Pb,.etc.,.with.a.
higher.sensitivity,.because.Bi(III).is.a.“softer”.oxidant.than.both.oxygen.and.mercury(II)..Taking.into.
account.all.side.reactions,.the.lowest.value.of.the.formal.redox.potential. E 0 f (Bi 3+ /Bi 0 ).was.obtained.
in.an.acidic.medium.containing.bromides.as.complexing.ions..Thus,.it.was.in.accordance.with.the.
known.relation.that.the.weaker.the.oxidant,.the.higher.the.sensitivity.of.measurements.in.PSA..Then,.
the. utilization. of. the. bismuth(III). species. as. an. “especially. gentle”. oxidant. would. lead. to. further.
improvements.in.the.detection.abilities.of.PSA.and.its.overall.analytical.performance.[626].
In. 2007,. antimony. ilm. electrodes. were. introduced. to. electrochemical. stripping. analysis.
[1995,1996],. and. analogous. new. procedures. were. presented. utilizing. antimony(III). salts,. which.
can. serve. as. an. oxidant. after. electrodeposition. of. metals. at. antimony. ilms. generated. onto. CPEs..
Compared.with.similar.total.substitution.of.traditionally.used.mercury(II).by.bismuth(III),.the.use.
of.antimony(III).offers.even.higher.sensitivity.in.the.detection.of.heavy.metals.[1994].as.the.weakest.
chemical.oxidant.from.the.three.Hg II ,.Bi III ,.and.Sb III .species..Of.course,.the.corresponding.constant.
current-based.stripping.chronopotentiometric.technique.was.examined.as.well.[1997].
Regarding. PSA. and. its. potentialities. in. practical. analysis,. yet. another. feature. should. not. be.
omitted.herein.and.is.illustrated.in.Figure.6.12,.making.a.comparison.between.the.electroanalyti-
cal.performance.of.both.ASV.and.stripping.potentiometry..This.confrontation.of.the.two.related.
techniques. was. made. with. the. same. sample. solution. and. identical. working. electrode,. a. bismuth.
ilm-plated.CPE..As.seen,.both.voltammograms.(in.the.DPASV.mode).had.exhibited.distinct.defor-
mations. of. the. baseline. with. a. large. maximum. (of. so. far. unclear. origin. [84]),. and. the. signals. of.
interest. were. badly. developed.. In. contrast,. the. respective. PSA. curves. were. much. favorable. and.
easily.evaluable.
This.test.is.a.textbook.case.of.how.the.result.of.an.analysis.may.rely.on.the.technique.chosen.for.
the.stripping.step..Since.voltammetric.measurements.are.based.on.the.detection.of.electric.current.
whose.origin.is.quite.diverse.(e.g.,.possible.trace.electroactive.impurities.and.their.residual.signal,.
non-faradic.phenomena.releasing.also.the.electric.current,.electrical.noise,.and.the.ohmic.current,.
etc.),.the.resultant.signal.may.suffer—and.usually.does.so—from.numerous.interferences..In.con-
trast.to.this,.the.potentiometric.stripping.regime.registers.the. E - t .dependence.(or.its.mathematical.
transformed.analogue,.respectively),.where.the.equilibrium.potential,. E EQ ,.represents.a.highly.selec-
tive.signal.independent.of.any.current-releasing.disturbance.[711,1984].
As.a.result,.the.interferences.under.comparable.conditions.were.severe.for.voltammetric.mea-
surements.but.almost.none.in.PSA..And.this.“insensitivity”.of.stripping.potentiometry.is.also.the.