Electroanalysis with Carbon Paste–Based Electrodes, Sensors, and Detectors - Electroanalysis with Carbon Paste Electrodes - page 203

pastes.with.other.phenols.and.polyphenols.like.epinephrine,.homovanillic.acid,.and.also.ascorbic.
and.uric.acids.which.usually.overlap.with.the.signal.[2957];.carbon.composites.are.applicable.as.
amperometric.detectors.in.CE.[559]..Ionic.liquids.and.nanostructured.carbon.materials.catalyze.the.
oxidation.or.improve.the.signal.of.the.analyte.[119,124,200,203,362,367,453,456,466,2958-2961]..
Some.catalysts.were.used.to.improve.the.electrochemical.oxidation.[2962-2964]..Some.of.the.main.
interference.in.biological.sample.are.AA.and.UA.which.overlap.with.the.signal.of.DA.with.unmodi-
ied.electrodes..Many.efforts.were.made.to.improve.the.analytical.situation.in.this.respect:.nega-
tively.charged.barriers.reject.the.anions.of.the.acids.if.the.pH.is.suficiently.high,.such.as.Naion.
membranes. [2961],. silica. gel. [1163],. silica. gel. with. phosphates. [1213,127],. zeolites. [700,1108],.
zeolite. with. Naion. [1136],. and. anionic. surfactants. [243,1654,1659,1661,2966,2967].. Polyalcohols.
[195,1747,2965].improve.the.resolution.of.the.signals.by.shifting.the.potentials.of.electrochemical.
responses.. Surfactants. in. general. have. a. strong. inluence. on. the. oxidation. signal. of. DA.. Stearic.
acid. has. long. been. used. as. a. modiier. for. carbon. paste. electrodes. for. in vivo . brain. electrochem-
istry.due.to.its.signal-resolving.effect.[1029];.nevertheless.the.application.seems.problematic.(see.
the.paragraph.on.brain.electrochemistry)..Neutral.surfactants.( Triton X100 ),.often.in.combination.
with. some. acid,. increase. the. signal. [317,1500,1634,1648,1649];. cationic. surfactants. improve. the.
resolution.of.overlapping.signals.[767,1632,2969-2972]..β-Cyclodextrin.forms.inclusion.complexes.
with.DA.and.supports.its.accumulation.[2974-2976],.and.so.do.electropolymerized.ilms.of.l-dopa.
[2977].and.nanoparticles.of.SiO 2 .[1008]..Various.types.of.nanoparticles.catalyze.the.oxidation.and.
decrease.the.overpotential,.such.as.Au.[2978,2979],.Pd.[969],.Ag.[416],.Fe.[976],.and.Ni.[972]..Ni(II).
[1616,2980],.SnO.[2981],.Fe(III).[1012],.cobalt.oxides.[1230],.ferrocenes.[881,986],.hexacyanofer-
rates.[1043,1044,1799,1802],.and.even.CdO.nanoparticles.[1003].can.act.as.oxidation.catalysts.
Some. complexes. of. Fe(II). [1617],. Cu(II). [2982],. Co(II). [1583],. and. Ru(III). [1612,2000].
are. also. active. in. this. respect.. Phthalocyanines. of. various. metals,. such. as. Cu. [519,2983],.
Fe(II). [933,1570,2984],. Co(II). [933,2984],. and. Mn(II). [912],. can. be. also. exploited. for. this.
task.. The. latter. in. combination. with. histidine. should. bio-mimic. dopamine. β-monooxygenase.
which. hydroxylates. DA;. it. is. assumed. that. hydrogen. peroxide. oxidizes. the. phthalocyanine,.
which. in. turn. extracts. electrons. from. the. analyte. whereupon. the. quinone. is. electrochemi-
cally. reduced.. Analogous. reaction. is. assumed. for. copper. phthalocyanine. [519].. Porphyrins.
of. Fe(III). [1202]. are. also. catalysts. for. the. oxidation. of. DA.. Apart. from. inorganic. compounds.
and. metallo-organic. complexes,. a. variety. of. organic. substances. have. been. used. as. elec-
trode. modiiers.. Acetone. [2986]. is. questionable. if. it. is. really. a. “modiier,”. or. if. it. just. dis-
solves. pasting. liquids. and. improves. the. physical. characteristics. of. the. surface.. Catalytically.
active.useful.substances.are.2,4-dinitrophenyl.hydrazine.[225],. N -hydroxysuccinimide.[2987],.
phenylenediamines. [992,1516],. quinones. and. hydroquinones. [992,995,1446,1462],. tetracyano-
quinodimethane. [2988],. Eriochrome. black. T. in. monomeric. [2989]. or. polymeric. form. [1763],.
pyrogallol. red. [1515],. hematoxylin. [443],. thionine. [1729],. Lamotrigine. [1645],. and. Eperisone.
[1633]..Electropolymerized.ilms.[135,1762,1763,1806,2991,2992].seem.to.have.a.positive.effect.
on.the.analytical.behavior..Biosensors.for.DA.contain.DNA.(interaction).[376],.HRP.(catalyti-
cally. oxidizing. the. analyte. with. the. aid. of. H 2 O 2 ). [2697],. quinoprotein. dehydrogenase. (using.
oxidized. phenols. as. electron. acceptors). [2786],. polyphenol. oxidase. [194,280,661,1495],. and.
tyrosinase.[78,1258,2779,2993,2994]..Quite.a.few.tissues.can.be.used.as.a.source.of.polyphenol.
oxidase.[276,279,1018,2123,2564,2756,2759,2995-3004,3266].
DA.metabolites.have.been.detected.chromatographically.with.CPEs.as.amperometric.detec-
tors.[3005,3006]..Epinephrine,.also.known.as.adrenaline,.can.be.adsorbed.and.electrochemically.
oxidized.[553,607,3007-3009];.surfactants.improve.the.signal.[3010-3012]..Mesoporous.alumi-
num. oxide-SiO 2 . supports. the. accumulation. [1855];. iodine. oxidizes. the. analyte. which. can. be.
detected.by.reduction.[3013]..Quite.a.few.compounds.were.found.to.exert.a.catalytic.effect.on.the.
oxidation.of.adrenaline,.such.as.Fe(III).on.zeolite.[1124],.phthalocyanines.[913,3014],.Methylene.
green.[3015],.hydroquinones.[993,3016],.and.a.carbothiamide.[3017]..Biosensors.for.epinephrine.
are.based.on.laccase.or.tissues.(crude.extract).as.a.pool.of.polyphenol.oxidase.[967,3018,3019].