Chemically Modified Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 99

functional.groups.likely.to.bind.metal.ions.before.their.electrochemical.detection.[808,1676-1684].
or. functionalized. polymers. (e.g.,. poly( N -vinylpyrrolidone);. [186,1685-1687]). with. adsorption.
properties.toward.organic.target.analytes.
A. special. category. also. associated. with. CPEs. belongs. to. molecularly. imprinted. poly-
mers.(i.e.,.macromolecular.compounds.formed.in.the.presence.of.a.molecule.that.is.extracted.
afterward,. thus. leaving. complementary. cavities. behind,. which. can. then. be. exploited. to.
the. selective. accumulation. of. the. original. molecule). [1688-1692].. Finally,. several. natural.
macromolecular. compounds. were. modiiers. of. CPEs.. The. most. popular. were. humic. sub-
stances. [297,837,1336,1693-1704],. which. were. mainly. applied. to. preconcentrate. heavy. met-
als. or. even. to. get. information. on. humate-metal. species. interactions. [837,1694,1696,1701]..
The. polysaccharide. chitin. [285,832,835,1705-1707]. and. its. deacetylated. form,. chitosan.
[86,88,499,835,1273,1465,1708-1711],. are. other. attractive. CPE. modiiers. applied. to. the. accu-
mulation. of. various. analytes. or. as. hosts. for. NP. catalysts. [86,417,. 499,950,1273,1465,1711]..
Other.less.common.natural.modiiers.are.lichens.[271,1712],.ionic.polysaccharides.(e.g.,.algi-
nate.derivatives.[464,479,1713]),.or.keratin.[287].
4.3.2.5.2 Ion Exchangers
Wang.and.coworkers.were.the.irst.to.report.the.incorporation.of.an.ion-exchange.resin.into.CPEs.
for. Cu 2+ . preconcentration. and. detection. [708].. Thereafter,. numerous. cation. exchange. and. anion.
exchange. resins. have. been. used. for. electroanalytical. purposes.. Cations. exchangers. involve. most.
often.a.polymeric.support.functionalized.with.sulfonate.or.carboxylate.groups.[708,1714]..The.most.
popular.cation.exchange.polymer.is.the.perluorinated-sulfonate.ionomer,.Naion,.which.was.largely.
applied.in.connection.with.CPEs..Examples.are.available.for.adsorptive.stripping.voltammetry.of.
cationic.analytes.such.as.metal.ions.[708,1354,1355,1364,1365,1714-1716].and.several.(usually.posi-
tively.charged).organic.species.[1717-1724].
Naion. was. also. used. in. CPE-based. biosensors. (enzyme. electrodes. [668,865,1725-1727]. and.
immunosensors. [1556,1558,1559,1728]).. Naion. was. sometimes. exploited. as. a. hosting. matrix. for.
ligands.[1354,1355,1364,1365],.charge.transfer.mediators.[1590,1729],.or.NP.catalysts.[467,496,1730]..
Other.cation.exchangers.include.the. Dowex 50W-X8 .resin.[522,713,807,1731-1734],.polyester.sulfo-
nate.ionomers.(e.g.,. Eastman Kodak AQ ).[922,1735],.and.several.commercially.available.resins.of.
the. Amberlite ® .trademark.(e.g.,. IR-120 .[252,904,1736],. IRC-718 .[1737-1740],.or. XAD-2 .[1741])..The.
anion.exchange.resins.were.essentially.nitrogen.polymers,. that is ,.quaternized.poly(4-vinylpyridine).
[1742-1744].and. Amberlite LA2 .[800,802,804,1736,1745,1746].
4.3.2.5.3 Permselective or Protective Coatings
CPE-based.biosensors.were.often.covered.with.polymeric.layers.to.protect.the.biomolecule.from.
the.external.solution,.to.prevent.from.surface.fouling.effects,.or.to.reject.interferences.. Naion ® .was.
mainly.used.for.this.purpose.[1725,1727],.but. Dextran .was.also.reported.to.improve.the.stability.of.
hemoglobin.immobilized.on.CILE.[512]..Ion-exchange.polymers.are.also.attractive.electrode.modi-
iers.when.used.as.thin.ilms.because.they.are.likely.to.induce.permselective.properties.(based.on.
charge.exclusion),.as.exploited.for.the.selective.determination.of.uric.acid.[1722]..Selective.detection.
of.dopamine.in.the.presence.of.ascorbic.acid.was.achieved.on.the.basis.of.a.poly(vinyl.alcohol)-
coated.CPE.[1747].
Other. permselective. or. protective. coatings. are. semipermeable. membranes—mostly. based. on.
size-exclusion. polymers—made. of. poly( o -phenylenediamine). [131,135,648,649,654,841,935,.
938-940,1261,1748-1779],. or. its. m -derivative. [921,1780],. poly(ethylene. oxides). as. poly(ethylene.
glycol). [319,862,1492,1519,1531,1566,1673,1781-1785],. and. poly( o -aminophenol). [247,1786]..
Other.macromolecular.stabilizing.additives.in.CPE-based.biosensors.include.poly(ethylene.imine).
[246,321,939,1494,1749,1787],. poly(dimethyl-siloxane). [20,1788,1789],. silicone-based. [1790],. or. a.
melanin-type.polymer.[1282].