Electroanalysis with Carbon Paste–Based Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 208

analyte. and. use. benzoquinone. or. phenazine. methosulfate. as. an. electron. acceptor. which. pro-
vides.an.anodic.re-oxidation.current.[786,1442].
Panthenol,.used.in.skin.ointments,.is.catalytically.reduced,.where.probably.the.carbonyl.group.of.
the.amide.moiety.is.reduced.to.the.alcohol,.which.can.be.further.reduced.to.the.amine.by.eliminat-
ing.H 2 O.[1622]..Phylloquinone.strongly.adsorbs.to.carbon.paste.and.is.determined.with.adsorptive.
stripping.voltammetry.with.open.circuit.accumulation.[3179].
Pyridoxal.can.be.bound.with.its.aldehyde.function.to.a.lipophilic.amine.yielding.a.Schiff.base.
-CH=N-.which.can.be.reduced.to.the.amine.[1637,1641].
Pyridoxine. is. oxidized. either. directly. [1398,3180]. or. catalytically. with. hexacyanoferrate(III).
or. V(IV)-Salen. (via. V V ). [1034,1585];. crown. ether. may. act. as. an. accumulator. [1398].. Ribolavin.
is. the. main. component. of. the. co-factor. of. lavoproteins,. FAD. and. FMN;. it. can. be. immobilized.
on. unmodiied. carbon. paste. or. on. silicagel. or. phosphate. sorbents. [39,1188,1198,1292-1294,3182].
and.is.also.used.for.the.catalytic.determination.of.NADH.[1292,1293]..Crown.ethers.form.supra-
molecular.complexes.with.the.analyte.[1398,1408]..Thiamine.is.catalytically.oxidized.by.Mn(II)-
phthalocyanine.(via.Mn III ).[906].
Also,. tocopherols. can. be. studied. [3184,3185]. and. determined. [3183]. with. carbon. paste. elec-
trodes..By.the.way,.α-,.β-,.and.γ-tocopherols.are.“the.pioneers”.among.vitamins.and.the.BIC.in.gen-
eral,.due.to.the.fact.that.they.were.successfully.recognized.in.a.mixture.and.subsequently.quantiied.
already.in.the.early.1970s.[37].
Quite.a.few.other.vitamins.are.detectable.with.CPEs,.such.as.vitamin.A.[3186-3188],.vitamins.of.
the.B-group.[232,1386,1486,3189],.vitamin.E.[3190-3192],.and.vitamin.K3.[1651]..One.method.for.
vitamin.B12.is.very.straightforward.by.mineralization.of.the.organic.compound.and.determination.
of.Co.via.adsorptive.stripping.with.a.hydroxamic.acid.[1386].

8.4.12 W hole C ells , M iCroorganisMs , T issues , and T issue e xTraCTs as M odiFiers
It.is.interesting.to.notice.that.various.microorganisms.and.tissues.have.relatively.often.been.used.as.
modiiers.for.carbon.pastes,.as.documented.in.an.overview.given.in.Table.8.26.
The.various.purposes.of.using.tissues.rather.than.puriied.single.compounds.are.as.follows:

. 1.. Sorption character .of.the.surface.of.microorganisms.or.tissues,.which.can.be.exploited.for.

accumulations.or.as.support.for.mediators

. 2.. Tissue.or.its.extract.as.a. source of an enzyme .or.another.important.biological.component.

without.the.need.of.time-consuming.clean-up.processes

. 3.. Monitoring .of.biological.processes

A. disadvantage. of. using. tissues. and. microorganisms. as. sources. of. biological. modiiers. is. the.
variation. of. the. target. compound. in. different. individuals,. and. frequently. also. within. the. tissue..
Individuals.of.this.type.of.biosensors.usually.have.individual.characteristics.
Algae.have.been.used.to.accumulate.metal.ions,.such.as.Au.[270,3193],.Cd.[2260],.Cu.[2226,.
2236,2245,2260,3194],.and.Pb.[3196]..Some.algae.have.been.employed.as.a.support.for.hexacyano-
ferrate.for.the.catalytic.determination.of.hydrogen.peroxide.[3195].
Bacteria.rarely.serve.accumulation.purposes.[2198,2199]..Otherwise,.they.are.exploited.as.a.source.
of.corresponding.dehydrogenases.or.oxidases,.like.for.ethanol.[780,2664,3197].and.glucose.[288,381,
1441,1443,1521,2863,2864]..Nicotinic.acid.is.hydroxylated.by. P. luorescens .with.quinones.as.electron.
acceptor.[786,1442].. Moraxella .metabolizes. p -nitrophenol.to. p -quinone.and.reduces.it.to. p -hydroqui-
none.which.is.more.electroactive.for.oxidation.than. p -nitrophenol.[2440]..Surface-expressed.organo-
phosphorous. hydrolase. on. Pseudomonas . hydrolyzes. organophosphorous. herbicides. with. ensuing.
degradation.of.the.released.nitrophenol.[2476]..The.respiratory.activity.of. P. luorescens .on.eggshell.
membrane.attached.to.carbon.paste.can.be.monitored.by.the.oxygen.consumption.[3198].