Electroanalysis with Carbon Paste–Based Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 193

8.4.2 a ldehydes , k eTones , and a Cids
Table.8.16.gives.an.overview.of.analytical.methods.based.on.carbon.paste.sensors.applicable.to.the.
determination. of. aldehydes,. ketones,. and. carboxylic. acid. which. are. important. in. biological. pro-
cesses..Other.methods.can.be.found.in.Section.8.2.
Aliphatic.aldehydes.can.be.reduced.to.alcohols.with.palladium-modiied.carbon.paste.electrodes.
in.alkaline.medium.[1268]..An.interesting.approach. for.the.determination.of.aromatic.aldehydes.
was.presented.by.Abruna's.group:.the.carbon.paste.was.modiied.with.a.complexed.aminopyridine,.
which.accumulates.aromatic.aldehydes.as.Schiff.bases;.the.latter.can.be.electrochemically.reduced.
[1021]..Ceresin.wax.as.a.binder.offers.increased.stability.against.organic.solvents.
A.biologically.important.ketone.(and.carbonic.acid).is.pyruvate;.it.can.be.detected.with.corre-
sponding.biosensors.based.either.on.pyruvate.oxidase.[781,1468].with.HRP.or.methyl.green.for.the.
detection.of.H 2 O 2 .or.on.pyruvate.dehydrogenase.with.vitamin.K3.as.a.co-factor.[2673].
Glycolate.is.enzymatically.oxidized.with.glycolate.oxidase.using.dimethylferrocene.as.an.elec-
tron. acceptor. [854,856].. Instead. of. the. puriied. enzyme,. biosensors. can. be. also. constructed. from.
tissues,.such.as.spinach.or.sunlower.leaves.[2674-2676]..The.sensor.with.spinach.leaves.can.be.also.
designed.for.electrogenerated.chemiluminescence.(ECL).with.luminol.(phthaloyl-hydrazide.[2675]).
Lactate.is.an.important.intermediate.in.energy.metabolism..Carbon.paste.sensors.for.lactate.are.
usually. designed. as. enzymatic. biosensors.. Most. frequently. lactate. dehydrogenase. (LDH). is. used.
for.this.purpose.which.oxidizes.lactate.to.pyruvate.[52,180,855,875,937,1000,1217,1475,1672,1771,.
1786,2677-2680]..Sensors.have.been.developed.for.the.d-.or.l-enantiomers.using.the.corresponding.
enzymes.. Catalysts. for. the. reoxidation. of. NADH. are. Meldola. blue. [1217],. ferrocene. or. naphtho-
quinone.in.combination.with.diaphorase,.an.enzyme.which.supports.the.reoxidation.of.NAD(P)H.
[855,875],.and.toluidine.blue.O,.preferentially.as.redox.polymer.[937,1475,1786,2677-2679].
Addition.of.alanine.aminotransferase.in.the.presence.of.glutamate.only.insigniicantly.suppresses.
the.interference.from.pyruvate,.but.is.effective.if.used.in.an.enzyme.reactor.[2679]..Glutamic.pyruvic.
transaminase.is.also.effective.for.the.removal.of.the.intermediate.pyruvate.with.glutamate.to.yield.
alanine.and. α -oxoglutarate.[1771]..Cytochrome. c .shows.electrochemical.activity.in.the.presence.of.
negatively.charged.lipids.(asolectin).and.acts.as.an.electron.acceptor.of.LDH.[1672];.it.can.be.replaced.
by.phenazine.methosulfate.Reineckate.[2680]..Diaphorase.in.combination.with.a.naphthoquinone.can.
be.used.to.reoxidase.NADH.as.an.enzymatic.intermediate.[855]..Cells.or.membranes.of. Paracoccus
denitriicans . can. be. used. as. a. source. for. membrane-bound. dehydrogenases. and. respiratory. chain.
enzymes.[1520].
Lactate. oxidase. can. be. used. as. an. alternative. to. LDH. in. biosensors. for. detecting. lactic. acid.
[246,364,647,661,863,1527,1567,2681-2684]..Mediators.for.the.detection.of.hydrogen.peroxide.are.Rh.
[647],.Pt.[1567],.MWCNT.[364,661],.Prussian.blue.[196],.and.peroxidases.[246,1527,2681,2683,2684]..
As.electron.acceptors,.Co-phthalocyanines.[1567],.ferrocene.[863,1527,2681,2682],.phenothiazines.
[863],.or.methylene.green.[1470].was.used..Yeasts.(baker's.yeast.or. Hansenula anomala ).can.be.the.
source.of.the.enzyme.and.of.cytochrome.b2.[1483,2685,2686]..Malate.dehydrogenase.can.recognize.
malate. in. corresponding. biosensors. with.toluidine. blue. O -polymers. [938].. Pd. nanoparticles. were.
used.as.modiiers.of.CPEs.in.an.amperometric.detector.of.capillary.zone.electrophoresis.[2687],.
showing.a.promising.way.also.for.other.platinum.metals.
Oxalic.acid.can.be.oxidized.with.Pd.nanoparticles.as.modiiers;.the.catalytic.reaction.proceeds.
via.Pd(II).[971,2688];.Os.(spongy).acts.similarly.[2689]..Lead.sulfate.as.a.carbon.paste.modiier.can.
preconcentrate.oxalate,.because.the.solubility.product.of.lead.oxalate.is.signiicantly.lower.than.
that.of.PbSO 4 ;.the.accumulated.oxalate.can.be.oxidized.to.carbon.dioxide.[811]..Co-phthalocyanine.
is.a.useful.catalyst.for.the.oxidation.of.oxalate.via.Co(III).[557,885,1172,1561,1822,2690-2692]..
Ruthenium. bipyridyl. silicotungstate. can. be. used. for. detection. of. oxalic. acid. with. ECL. [1017]..
Biosensors.for.oxalic.acid.involve.oxalate.oxidase.via.detection.of.H 2 O 2 .[1182,2693].
Salicylate. (or. salicylic. acid,. a. close. derivative. to. acetylsalicylic. acid. forming. well-known.
Aspirin ,.being.of.interest.also.in.the.previous.Section.8.3).can.be.determined.with.the.aid.of.some.