Instrumental Measurements with Carbon Paste Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 145

electrode.surface.had.not.yet.been.included.among.electroanalytical.techniques.by.the. International
Union of Pure and Applied Chemists .( IUPAC )..However,.as.admitted.by.its.proponents.themselves,.
the. technique. should. be. referred. to. more. accurately. as. chronopotentiometric. stripping. analysis.
(again,.see.in.[1977])..This.alternative.arose.from.ASV.and,.in.both.techniques,.metals.in.a.sample.
are.electrolytically.deposited.on.an.electrode..The.two,.however,.differ.in.the.way.in.which.depos-
ited.metals.are.stripped.off.and.the.analytical.signal.obtained..In.PSA,.no.control.is.made.of.the.
potential.of.the.working.electrode.during.metal.stripping,.which.is.accomplished.by.using.a.chemi-
cal.oxidant.in.solution.(originally.Hg(II).or.dissolved.oxygen)..The.working.conditions.are.set.in.
such.a.way.that.the.rate.of.oxidation.of.deposited.metals.remains.constant.throughout.the.stripping.
process;.such.a.rate.is.determined.by.the.oxidant.diffusion.from.the.solution.to.the.electrode.surface.
[1982-1987]..Under.these.conditions,.the.analytical.signal.is.recorded.by.monitoring.the.potential.of.
the.working.electrode.as.a.function.of.time;.the.distance.between.the.two.consecutive.inlex.points.
in.a.curve.(stripping.time).is.proportional.to.the.metal.concerned.in.solution,.whereas.the.potential.
of.the.central.zone.(formal.redox.potential,. E 0 f ).is.a.characteristic.measure.for.that.
Modern.PSA.instruments.use.microcomputers.to.register.fast.stripping.events.and.convert.the.
wave-shaped. response. to. a. more. convenient. peak. over. [1983-1985,1987].. Then,. the. number. of.
counts.can.be.registered.in.differential.units,. dt/dE .(s.·.V −1 ),.when.the.peak.area.is.evaluated.in.sec-
onds,.corresponding.to.the.stripping.time.(see.Figure.6.11.[1991]).
According.to.Jagner.[1982].and.some.of.his.continuators.(e.g.,.[1983-1985]),.stripping.potentiom-
etry.can.be.classiied.into.two.major.modiications.(i).PSA.with.chemical.oxidation.and.(ii) constant-
current.stripping.analysis.(CCSA),.both.existing.in.a.number.of.further.variants.proposed.later.on..
Namely,.they.are.as.follows:. reductive PSA ,. adsorptive PSA ,. derivative PSA ,. differential PSA ,. kinetic
PSA ,. multichannel-monitoring PSA ,. oxidative CCSA ,. reductive CCSA ,.and,.inally,. constant-current-
enhanced PSA ..In.this.survey,.however,.some.terms.mean.only.the.different.naming.for.the.already.
existing.technique,.which.is.the.case.of.the.latter.being.one.of.the.CCSA.variants.
In. measurements,. where. the. species. accumulated. at. the. working. electrode. are. to. be. reduced,.
either.chemical.reductants.or.a.constant.current.are.applied.in.the.stripping.step.[1982,1984,1987]..
Whereas. the. irst. approach. is. seldom. used. (see,. e.g.,. [1986]),. the. constant. current. with. negative.

Memory

0
0
0

E c

A 0

3

5

L

E A

E a

t

Counts

E

E

I II III

FIGURE 6.11 Example. of. a. stripping. potentiogram.. (I). Potential. vs.. time. dependence. of. working. elec-
trode.during.redissolution.of.three.amalgamated.metals.in.the.potential.window.of. E a .−. E c ..(II).Computer.
memory.section;.the.data.storage.area.starting.at.address. A 0 .holds.a.record.of.accumulated.clock.pulse.counts..
Right (III):. the. resultant. multichannel. chronopotentiogram.. (Reproduced. from. Mortensen,. J.. et. al.,. Anal.
Chim. Acta ,.112,.297,.1979..With.permission.)