Instrumental Measurements with Carbon Paste Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 144

200

100

RW-B/SO

0

E (mV)

-100

CR-5/SO

-200

-300

cGE

-400

0 2 4 6 8 10 12 14

pH

FIGURE 6.10 Calibration.curves.for.pH-measurement.obtained.with.two.different.bare.carbon.pastes.and.with.
the.commercial.pH-probe..CR-5/SO,.full.line:.carbon.paste.from.carbon.gear.lubricant.and.silicone.oil,.RW-B/
SO,.dashed.line:.….from.high-grade.spectral.graphite,.cGE,.dotted.line:.combined.glass.sensor.( Metrohm ).. Note :.
Due. to. unstable. response. of. the. RW-B/SO,. light. points. were. plotted. as. “rough”. average. values.. (According. to.
Rejhonová,.H.,.Development.and.testing.of.the.dual.sensors.based.on.carbon.pastes.modified.with.Bi.+.Bi 2 O 3 .and.
Sb.+.Sb 2 O 3 .mixtures..MSc.dissertation.(in.Czech),.University.of.Pardubice,.Pardubice,.Czech.Republic,.2011.

electrode.surface.decreases.from.the.starting. c 0 .value.to.zero..Under.conditions.of.linear.diffusion.
with. no. kinetic. complications,. the. relationship. between. the. transition. time. and. concentration. is.
given.by.Sand's.equation:

1 2 / 1 2 / 0

p ⋅ n F A D ⋅ ⋅ ⋅ c

1 2 /

t =

. (6.37)

2 ⋅ I

.

where
I .is.the.applied.current
n .is.the.number.of.electrons.transferred.at.electrode.reaction

−
ne Ox + Red . (6.38)

.

where
F .is.Faraday's.constant
A .is.the.electrode.surface.area
D .is.the.diffusion.coeficient.of.the.reacting.substance
c 0 .is.the.starting.concentration.of.the.reacting.substance

As. evident. from. the. equation,. measurement. of. transition. time. can. be. used. for. determination. of.
electroactive.substances.in.the.analyzed.sample,.but.the.method.found.a.limited.application.only.in.
practical.electroanalysis.[1981,1998]..Nevertheless,.ive.papers.employing.CPEs.in.chronopotentio-
metric.studies.appeared.in.the.literature.[13,20,26,190,1999].
Much.more.important.and.frequent.is.stripping.chronopotentiometry,.introduced.by.Jagner.and.
Graneli.in.1976.[1982]..At.that.time,.this.novel.analytical.technique.for.the.determinations.of.heavy.
metal. traces. was. called. potentiometric. stripping. analysis. (PSA),. because. analyses. based. on. the.
oxidation.of.species.previously.deposited.on.an.electrode.by.oxidant.currents.convectively.to.the.