Chemistry Reference
In-Depth Information
to.the.cathodic.barrier,.and.that.of.Zn
2+
.cannot.be.detected.at.all.on.unmodiied.CPE,.whereas.
all.of.these.metal.ions.are.easily.determined.using.mercury.electrodes.(because.of.the.extended.
cathodic.potential.range).
An.elegant.way.to.overcome.this.limitation.is.to.resort.to.metal-plated.CPEs.(with.mercury,.bis-
muth,.or.even.antimony.ilms),.enabling.the.reduction.of.metal.ions.in.an.amalgam.form..As.shown.
in.Tables.8.5.and.8.6,.the.approach.was.sometimes.used.for.Pb.determinations,.more.often.for.the.
amperometric.detection.of.Cd,.and.systematically.for.Zn.electroanalysis.(except.in.the.case.of.poten-
tiometric.detection.[1974])..Regarding.the.individual.conigurations,.the.heterogeneous.character.and.
a.kit-like.concept.of.carbon.pastes.naturally.led.to.a.variety.of.applicable.conigurations..The.most.
common.metallic-ilm.electrodes.as.well.as.some.related.arrangements.are.shown.in.Figure.8.4.
Besides.the.most.frequent.variants.of.BiF-CPE,.Bi-CPE,.and.SbF-CPE.described.in.several.reports,.
this.igure.also.includes.a.rather.curious.coniguration.of.
bismuth paste electrode
.(
BiPE
.[266]).that.
is—to.the.authors'.knowledge—the.only.example.of.functioning.paste-like.mixture.that.does.not.con-
tain.any.carbon/graphite.moiety..(Despite.its.rather.poor.performance,.the.BiPE.seems.to.be.the.irst—
but.still.very.little—step.in.seeking.the.way.how.to.devise.a.bismuth.dispersion-based.sensor.[268].that.
could.be.an.environmentally.friendly.alternative.to.Heyrovsky's.dropping.mercury.electrode.[2408].)
A. huge. amount. of. work. has. been. made. on. lead. (and. cadmium;. see. Table. 8.5). because. of. the.
presence. of. these. toxic. species. at. nonnegligible. levels. in. various. natural. samples.. Methods. are.
available.for.analysis.of.several.aqueous.media,.including.natural.(tap,.river,.lake,.sea,.ground,.and.
well).waters.and.wastewaters.(polluted.waters,.industrial.efluents,.and.electroplating.baths),.solid.
samples. (sediments. and. food. products),. or. biological. matrices. or. pharmaceuticals.. More. speciic.
samples. are. atmosphere. (especially. for. Cd),. human. hair. (Pb. and. Cd),. and. gunshot. residues. (Pb).
[807,1836,2259,2275]..Again,.as.for.Hg.and.Cu,.better.sensitivity.and.selectivity.was.achieved.when.
applying. a. preconcentration. step. prior. to. the. electrochemical. detection.. This. was. made. possible.
by. means. of. electrode. modiiers. exhibiting. complexation,. sorption,. or. ion. exchange. properties..
Molecular.ligands.or.chelates.can.be.used.in.principle.but.better.long-term.stability.was.obtained.
when.incorporating.solid.macromolecular.compounds.(e.g.,.organic.resins.and.organic-inorganic.
hybrid.solids)..Many.methods.were.applicable.to.the.simultaneous.detection.of.lead.and.cadmium,.
sometimes.also.with.zinc.[103,617,623,2283].
Cd
Pb
Cd
Pb
Bi-PE
BiF-CPE
Pb
Cd
SbF-CPE
10 μA
Bi-CPE
2
μA
Sb-CPE
MF-CPE
-1.2
-1
-0.8
E
[V] vs. Ag/AgCl
-0.6
-0.4
-0.2
-1
-0.8
E
[V] vs. Ag/AgCl
-0.6
-0.4
(A)
(B)
FIGURE 8.4
Square-wave.anodic.stripping.voltammograms.of.Cd
2+
.+.Pb
2+
.model.mixtures.at.different.types.
of.metal.ilm-plated.and.metal-modiied.carbon.paste.and.paste.electrodes..MeF-plated.(A).and.Me-modiied.
(B).electrodes;.the.individual.types.as.inscribed..
Experimental conditions
:.silicone.oil-based.carbon.paste.
[the.same.for.all,.except.BiPE.made.of.bismuth.powder.(50%,.m/m).+.silicone.oil.(SO);.content.of.both.metals.
in.Bi-CPE.and.Sb-CPEs,.17%.(m/m)];.SWASV:.
f
SW
.=.25.Hz,.Δ
E
.=.50.mV,.s.i..=.4.mV;.s.e.:.0.01.M.HCl.(pH 2);.
c
(Hg,Bi,Sb).=.1.×.10
−5
.mol.·.L
−1
.(for.A);.
c
(Cd,Pb).=.50.ppb.(for.A),.25.ppb.(for.B);.accumulation.conditions:.
E
ACC
.=.−1.2.V.(A),.−1.0.V.vs..ref.,.
t
ACC
.=.120.s,.
t
EQ
.=.15.s.(B);.potential.limits,.from.−1.2.V.to.−0.2.V.vs..ref..
(Redrawn.and.rearranged.from.Švancara,.I..et.al.,.
Cent. Eur. J. Chem
.,.7,.598,.2009.)
Search WWH ::
Custom Search