Instrumental Measurements with Carbon Paste Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 134

6.3 AMPEROMETRY
Amperometry.is.the. monitoring of the current .in.dependence.of.a.parameter,.such.as.volume.of.a.
reagent.(titration).or.time.(chronoamperometry)..In.a.more.general.sense,.amperometry.is.a. special
case of voltammetry ,.when.the.potential.(ramp).is.set.constant,.at.a.ixed.value.that.is.to.be.chosen.in.
a.way.to.enable.the.full.electrochemical.transformation.of.the.redox.species.analyzed..In.principle,.
amperometry. can. be. applied. to. static. (batch. analysis,. stop-low. systems). and. dynamic. solutions.
(stirred.solutions,.low.systems).
Static.conditions.usually.prevail.if.the.current.is.measured.and.used.directly.for.the.evaluation.
of.the.concentration.of.the.analyte,.either.by.external.calibration.curves.or.by.the.standard.addition.
method..Dynamic.conditions.are.found.when.the.solution.is.moved.relatively.to.the.electrode,.which.
is.the.case.in.stirred.solutions.or.in.low.systems..The.instrumental.setup.for.amperometry.is.usually.
equivalent.to.that.of.voltammetry,.usually.comprising.three.electrodes.(working.electrode,.reference.
electrode,.and.auxiliary.electrode)..As.mentioned.earlier,.the.operating.potential.is.usually.set.to.a.
constant.value,.where.the.limiting.current.of.the.target.species.can.be.monitored,.which.is.directly.
proportional.to.the.concentration.of.the.analyte.in.the.solution.
In. chronoamperometry,. considerations. of. the. potential. step. experiment. (see. Section. 6.1). can.
be.applied..A.chronoamperometric.potential.step.measurement.is.either.the.application.of.a.single.
constant.potential.starting.with.open.circuit.conditions.or.it.includes.two.constant.potentials.(double.
step.experiments),.jumping.from.one.potential.to.another.

•. Hydrodynamic amperometry (HA) . is. the. monitoring. of. currents. at. a. constant. potential.

under. hydrodynamic. conditions,. usually. in. stirred. solutions.. In. fact,. rotated. electrodes.
or.moving.streams.of.solutions.are.also.possible..Hydrodynamic.amperometric.measure-
ments.can.be.useful.for.investigating.sensor.response.times.and.stabilities.or.to.perform.
quantitative.determinations.

•. Hydrodynamic voltamperometry (HVA) .is.the.recording.of.(usually.steady.state).currents.

under.hydrodynamic.conditions.in.dependence.of.a.potential;.such.voltamperograms.are.
very.useful.to.ind.optimal.operating.potentials.

•. Amperometric detection (AD) .is.a.general.term,.where.the.amperometric.measuring.sys-

tem.is.combined.with.a.system.under.hydrodynamic.conditions,.for.example,.low.systems.
such.as.low.injection.analysis.(FIA),.sequential.injection.analysis.(SIA),.batch.injection.
analysis.(BIA),.or.analytical.separation.(column.chromatography,.capillary.zone.electro-
phoresis,.etc.).

•. Flow injection analysis ,. designed. by. Ruzicka. and. Hansen. [1947],. exists. in. its. simplest.

form.as.a.device.consisting.of.a.pump,.an.injector,.and.a.detector..The.task.of.the.pump.can.
be.even.taken.over.by.gravitation..A.carrier.is.transported.constantly.through.the.system;.
injection. of. an. electroactive. component. produces. a. transient. signal. at. the. detector.. The.
system.is.versatile.because.reagents.can.be.admixed.and.reactors.can.be.inserted..It.is.an.
ideal.method.for.testing.and.optimizing.analytical.conditions.and.is.very.often.used.for.
investigations.with.biosensors.

•. Sequential injection analysis ,.considered.as.a.second-generation.low.injection.technique,.

consists.of.a.high.precision.pump.that.can.be.operated.in.both.directions,.a.holding.coil,.
and. a. multidelivery. valve. that. is. connected. to. various. reagents. and. to. the. sample. solu-
tion..At.the.beginning,.the.system.is.illed.with.the.carrier;.then.sequentially.sample.and.
reagents.are.aspired.as.a.stack.and.eventually.brought.to.the.holding.coil,.where.due.to.the.
parabolic.zone.proiles.and.supported.by.a.fore.and.back.movement.caused.by.the.pump,.
mixing. occurs.. The. sample-reagent. cocktail. is. inally. pumped. through. the. valve. to. the.
detector..The.indisputable.advantage.of.SIA.over.FIA.is.a.considerably.lesser.consumption.
of.solvents.and.reagents.