Chemistry Reference
In-Depth Information
AA.is.readily.oxidized.at.low.positive.potentials.already.and.can.be.determined.directly.[453,456,.
458,1029,2957,3140,3145];.hexadecyl.sulfonate.shifts.the.potential.to.more.anodic.direction.by.elec-
trostatic. repulsion. [1661],. cationic. surfactants. [783,2969-2972],. stearic. acid. [1029,2002],. ionic. liq-
uids.[453,456,458,3147],.carbon.ceramic.[3009],.carbon.nanotubes.[123],.and.carbon.nanoibers.[660].
improve.the.signals.and.in.many.cases.also.the.resolution.from.other.analytes,.in.particular.from.DA.
and.UA..Enhancement.can.also.be.achieved.by.intimate.anodization.of.the.CP-surface.[63,210],.regard-
less.of.which.detection.technique.is.used;.see.Figure.8.17.with.the.choice.of.stripping.potentiometry.
Cyclodextrine.and.mesoporous.silicagel.facilitate.adsorptive.accumulation.[3148-3150]..Cu(II).
rather.than.Cu(I).forms.complexes.with.AA,.which.can.be.reduced.at.slightly.negative.potentials.
[1316]..At.positive.potentials.Cu(I)-oxide.can.be.used.to.oxidize.the.analyte.[1229];.catalytic.oxida-
tion. also. occurs. with. Cu(II)-phosphate. [3151],. Cu(II)-phthalocyanine. [3152],. hexacyanoferrates.
[1043,1044,1094,1742,1799,1802,1820],. immobilized. Fe(III). [1110,1122,1704,3153],. pentacyano.
nitrosyl.ferrate(II).[3154,3155],.ferrocenes.[870,874,1528,1542,1548,1549,3130,3155-3160].and.other.
Fe-complexes.[1202,1617],.phthalocyanine.[653,655,916,930,933,1570,3161,3162],.Co(II)-complexes.
[1583,1586,1590],. Ru(III)-complexes. [86,1609,1610,1612,2985],. Zn-azamacrocycles. [3163],. vana-
dates. [144,3164],. phosphomolybdate. [3165],. CdO. nanoparticles. [1003],. and. Pd. and. Ag. nanopar-
ticles.[416,969]..Also.organic.compounds.catalyze.oxidation,.such.as.quinones.and.hydroquinones.
[53,422,1446,1460,1461],.tetramethyl.phenylenediamine.[1516],.chloranil.[3166],.4-nitrophthaloni-
trile.[3131],.thionine.[438,1509,1729],.TCQM.[3167],.TTF.[1491],.calixarene.with.Pb(II).[1430],.vari-
ous.organic.polymers.[135,1764,1806,2964,3168,3169],.monomeric.and.polymeric.Eriochrome.black.
T.[1763,2989],.Methylene.blue.[1087,1285,1288,1318,3170-3172],.Methylene.green.[1472],.Meldola.
blue.[1209,3173],.Brilliant.yellow.[1186],.and.Congo.red.[3174]..HRP.[2681].acts.catalytically.via.
Fe(II).in.heme;.other.biosensors.can.be.made.from.plant.tissue.[3175,3176]..AA.can.also.be.deter-
mined.indirectly.by.suppressing.the.electrochemiluminescent.signal.of.luminol.[3177].
Vitamins. of. the. B. group,. such. as. folic. acid. [1663],. nicotinamide,. pyridoxine,. ribolavin.
[1397],. and. nicotinic. acid. [1246,3178],. give. electrochemical. responses. at. carbon. pastes.. The.
latter.can.be.also.determined.with.
Pseudomonas luorescens
.whole.cells;.they.hydroxylate.the.
HO
HO
O
O
H
2
HO
OH
d
t
d
——
0.2 s V
-1
1
-0.2
0
+0.2
+0.4
+0.6
+0.8
E
[V] vs. Ag/AgCl
FIGURE 8.17
Oxidation.of.l-ascorbic.acid.(AA).at.unmodiied.carbon.paste.electrode.(1).and.at.the.same.
electrode.with.electrolytically.activated.surface.(2)..
Experimental conditions
:.silicone.oil-based.CPE;.constant.
current.stripping.analysis.(CCSA),.deposition.potential,.−0.5.V.vs..ref.;.deposition.time,.15.s;.equilibration.time,.
10.s;.stripping.step:.−0.2.→.+0.8.V.vs..ref.;.stripping.current,.+1.μA;.1.M.acetate.buffer.(pH.4.5),.
c
(AA).=.5.×.
10
−4
.mol.·.L
−1
;.activation.procedure.(prior.to.CCSA),.
E
AND
.=.+1.75.V.(for.120.s).+.
E
CATH
.=.−1.0.V.(15.s),.0.1.M.
Na
2
HPO
4
.+.0.05.M.H
3
PO
4
.(pH.9)..(Redrawn.and.rearranged.from.Švancara,.I..et.al.,.
Anal. Sci
.,.18,.301,.2002.)
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