Chemistry Reference
In-Depth Information
An HPLC-tandem MS (HPLC-MS
2
) method characterized by minimal sample preparation,
highsensitivity,andselectivitywasdevelopedforthedeterminationofcyclamateinfoods.Under
negativeESIconditions,parentionsof
m/z
=177.9andproductionsof
m/z
=79.9werecollectedand
usedforquantitation(SheridanandKing2008).
4.15.5 Determination of NhDC
TheHPLC-UVmethodseemstobethemostpopularoptionforthedeterminationofNHDC.
NHDC can be analyzed using a standard C
18
column in gradient mode. The optimal analytical
wavelength is 282 nm, since common food components (e.g., sweeteners and preservatives) are
transparentorabsorbveryslightlyatthiswavelength(Nakazatoetal.2001).
NHDCisaminorcomponentofsweetenerblends.Itwasseparatedfromothercommonlyadded
sweetenersusinga100-mMboratebuffer(pH8.3).DirectUVdetectionwasapplied,andawave-
lengthof282nmwasfoundoptimaltoavoidinterferencesfromothersweetenersandsugars.The
methodwassuccessfullyappliedtothedeterminationoflowlevelsofNHDCinsoftdrinks,fruit
juices,andyogurts(Pérez-Ruizetal.2000).
4.15.6 Determination of Saccharin
Inthelastfewyears,therehasbeenaninterestinthedevelopmentofanalyticaldevicesforthedetec-
tionandmonitoringofvariousbiologicalandchemicalanalytes.Forseveraldecades,analyticalchem-
istswereinspiredfromthebiologicalsciences,andnowadays,thedetectionofanalytesusingbiosensors
isverycommon.Biosensorsofferthecapabilitytodevelopmethodsfortherapidscreeningofsaccharin
witharespectivelowcost(NikolelisandPantoulias2000).Lipidilmscanbeusedfortherapiddetec-
tionorcontinuousmonitoringofawiderangeofcompoundsinfoods.Suchelectrochemicaldetectors
aresimpletofabricateandcanprovideafastresponseandhighsensitivity.Themajorinterferencefrom
proteinscanbeeliminatedbymodulationofthecarriersolutionthatdoesnotallowadsorptionofthese
compoundsinBLMs(Nikolelisetal.2001b).Aconductometricmethodbasedontheuseofsurface
s-BLMsisdevelopedformonitoringsaccharinandothersweeteners.Theinteractionsofsweeteners
withs-BLMsproduceareproducibleelectrochemicalioncurrentsignalincreasethatappearswithina
fewsecondsafterexposureofthemembranestothesweetener.Thecurrentsignalincreasesrelatively
totheconcentrationofthesweetenerinbulksolutioninthemicromolarrange(Nikolelisetal.2001a,b).
Recently,ananohybridmembranesensorhasbeenproposed(artiicialBLMs)andhasbeencompared
withthesurfaces-BLMsofferinghigherstability(ChalkiasandGiannelis2007).
Potentiometryisatechniqueinwhichasinglemeasurementofelectrodepotentialisemployed
todeterminetheconcentrationofanionicspeciesinasolution.Apotentiometrictechniqueischar-
acterizedbytheselectivity,thestability,andtheresponsetimeoftheelectrodeused.Theselectivity
of the electrode is generally evaluated considering some important ionic species normally found
ascomponentsinfood.Stabilizationandresponsetimesareevaluatedbyrecordingthepotential
responseofthemembraneversustime,astheconcentrationofsaccharinincreasesinsolution.Drift
isdeterminedbymeasuringchangesofelectrodepotentialwithtime,inaixedsaccharinconcen-
trationsolution.Inliterature,anumberofelectrodesareproposedforpotentiometricdetermination
of saccharin in foodstuff with speciic selectivity, stability, and response time properties in each
case.Apolymer(silsesquioxane3-n-propylpyridiniumchloride)coatedgraphiterodion-selective
electrodewithfastresponsetimeshasbeenproposed.Theelectroderesponsewasbasedontheion
pairformedbetweensaccharinateacidandthe3-n-propylpyridiniumcationfromthesilsesquiox-
anepolymer(Alfayaetal.2000).Asilverwireelectrode(Assumpcaoetal.2008)hasalsobeen
proposed demonstrating great stability and lifetime. An electrode based on a polypyrrole-doped
membraneisdeveloped,exhibitinghighselectivitytowardsaccharininthepresenceofothercom-
poundscommonlyfoundinfood(Álvarez-Romeroetal.2010).
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