Electroanalysis with Carbon Paste–Based Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 180

Ti IV

10 μA

(e)
(d)
(c)
(b)
(a)

-1.2 -1.0 -0.8 -0.6

E [V] vs. ref.

-0.4 -0.2 0 +0.2

FIGURE 8.9 Differential.pulse.voltammetry.of.titanium(IV).at.a.carbon.paste.electrode.modiied.' in situ '.
with.oxalic.acid..Model.calibration..(a).0,.(b).25,.(c).50,.(d).75,.and.(e).100.μg.·.L −1 .Ti(IV).. Experimental condi-
tions :.Nujol.oil-based.carbon.paste;.DPV,.accumulation.conditions:. t ACC .=.2.min,. E ACC .=.−1.2.V.vs..Ag/AgCl,.
scan. rate:. 50.mV.·.s −1 ;. s.e.:. 0.05.M. acetate. buffer. +. 0.01.M. H 2 C 2 O 4 .. (For. other. parameters. and. details,. see.
Stadlober,.M..et.al.,. Talanta ,.43,.1915,.1996;.Stadlober,.M..et.al.,. Sci. Pap. Univ. Pardubice Ser. A ,.3,.103.)

target.metal.species).was.often.applied..On.the.other.hand,.direct.electrochemical.methods.involved.
potentiometry,.exploiting.electrostatic.interactions.between.charged.forms.of.the.analyte.and.suit-
able. modiiers,. and. sometimes. also. the. direct. voltammetric. detection. mode. (restricted. to. date. to.
Ti IV O 2 2+ .and.Ga 3+ .species)..The.studied.matrices.were.mainly.water.solutions.and.ore.specimens,.
which. were. also. the. cases. of. a. method. for. determination. of. Ti(IV). illustrated. in. Figure. 8.9. (on.
model.calibration).and.based.on. in situ .modiication.with.oxalate.that,.under.slightly.altered.condi-
tions,.had.also.been.applicable.to.V(V).and.Mo(IV).
Recently,. efforts. have. been. made. to. detect. rare. earth. metals.. In. addition. to. the. aforemen-
tioned. strategy. involving. electroactive. ligands. such. as. Alizarin. derivatives,. novel. approaches.
have.exploited.the.attractive.features.of.room-temperature.ionic.liquid-based.CPEs.(as.such.or.
“doped”. with. carbon. nanotubes). for. the. potentiometric. detection. of. lanthanide. or. actinide. cat-
ions,. even. in. complex. mixtures. (see,. e.g.,. [2361]).. Ionophores. were. sometimes. added. into. the.
composite. electrode. to. improve. sensitivity. and. selectivity. of. the. method. via. strong. interaction.
effects.[415,419,510,511].

8.1.7 M eTals oF a lkaline e arThs and a lkaline M eTals
This.family.(namely,.Li,.Na,.K,.Cs,.Be,.Mg,.and.Ca).constitutes.a.special.class.of.analytes.as.most.alkali.
metal.and.alkaline.earths.metal.ions.are.not.electroactive.in.the.sense.that.they.cannot.undergo.electron.
transfer.reactions.at.electrode.surfaces,.at.least.under.usual.conditions..It.is.therefore.not.so.surprising.
to.ind.potentiometry.at.the.top.place.among.electrochemical.techniques.applied.to.determine.these.
species.using.CPEs.(see.irst.half.of.Table.8.9)..To.this.end,.CPEs.were.modiied.with.selected.iono-
phores.(e.g.,.macrocyclic.compounds).or.ion-exchangers.to.induce.preferable.recognition.via.host-guest.
interactions..The.only.exception.is.the.Be 2+ .ion,.which.can.be.detected.by.cathodic.reduction.[2342].