Chemistry Reference
In-Depth Information
InthemostcommonmodeofSPE,analiquotofthesampleextractisloadedontoaprevi-
ouslyconditionedSPEcartridge.ThetypeofSPEpackingmaterial,solvents,pH,andthelow
ratesneedtobeproperlyselectedinordertoretainanalyteseffectivelywithinthecartridge.The
interferingsubstancesshouldberetainedverystronglyornotretainedatall.Asaresult,weakly
retainedsubstancesarereadilyremovedfromthecartridgeduringsampleloadand/orcartridge
wash. Analytes are eluted during the elution step, and interfering substances having a strong
afinitytothesorbentstayadsorbedwithinthecartridge.Thesensitivityofainaldetermination
caneasilybeenhancedbyevaporatingtheinalSPEextracttodrynessandreconstitutingitwith
asmalleramountofasolventofchoice(preconcentration).SPE-basedsample-preparationpro-
tocolsseemtobethebestavailablechoice.Theyaresimple,reproducible,reasonablyquick,and
inexpensive.Theyareuniversalandcompatiblewiththemostpopulartechniquesusedinfood
analysis(Tunick2005).
Sweetenedbeveragesincludetwotypesofbeverageswithcarbondioxideandtwotypesofbev-
erageswithoutcarbondioxide.Beverageswithcarbondioxideincludesoftdrinks“light”andsoft
drinkssugar-sweetened.Beverageswithoutcarbondioxidealsoincludethesametypesofbever-
ages:softdrinks“light”andsoftdrinkssugar-sweetened.Insoftdrinks“light”withcarbondiox-
ide,amixtureofASPandACS-Kismoreoftenusedtosweetentheproducts(Lethetal.2007).
Micellarelectrokineticcapillarychromatography(MEKC)isarapidmethodforthedetermination
ofartiicialsweetenersinlow-caloriesoftdrinksandisoftenused.Thesamplesolutionsof“light”
softdrinksarepreparedbydilutingtheproductswithanappropriateamountofdeionizedwater.
The solutions are then simply iltered through a 0.45-μm cellulose acetate ilter before analysis
(Thompsonetal.1995).
Today,themostcommontechniqueforthedeterminationofartiicialsweetenersinsoftdrinks
is high-performance liquid chromatography (HPLC) analysis. The sample preparation for HPLC
analysisincludesirstlyilteringthrougha0.45-mmmembraneilter,andthenthesampleisultra-
sonicatedbeforetheanalysis.Nectarsareirstcentrifuged,ilteredthroughmembraneilters,and
thenultrasonicated(Linoetal.2008).Forthedeterminationincoladrink,irstavolumeisaccu-
ratelyweighedintoavolumetriclaskandthendegassedinanultrasonicbath.Ifthedetermination
isobtainedthroughHPLCanalysis,thevolumeofcoladrinkisdirectlydilutedwithmobilephase
(Demiralayetal.2006).
Gumsamplesarepreparedbyplacingthesampleinalaskandextractingwithamixtureofgla-
cialaceticacid,water,andchloroform.Hardorsoftcandysamplesareshakenwithwateruntilthey
dissolve(Biemer1989).Milkanddairyproductsarehomogenizedpriortoanalysis,andanaliquot
ofahomogeneoussampleistransferredtoalaskfollowedbytheadditionofdistilledwater.The
mixtureisthoroughlystirredandallowedtostandandtheniltered(Nietal.2009).
Sweetenersaredeterminedindietjamsbymixingthejamwithwaterandsonicatingthemix-
ture.Themixtureismadeuptovolumeandthenilteredthrougha0.45-mmilter(Boyce1999).
Preservedfruitisgroundedandhomogenized.Thenitisweighedintoavolumetriclask,andwater
isadded.Thismixtureisextractedultrasonicallyanddilutedtovolumewithwateraftercoolingto
roomtemperature.AvolumeofsupernatantisappliedtoaconditionedSep-PakC
18
cartridge(Chen
andWang2001),andthesubsequentSPEfollowsaccordingtothepreviousprotocol.
Thedeterminationofsweetenerswithlowinjectionanalysis(FIA)methodsisverycommon.
Itisreportedthatbeverages,juices,strawberrysweets,andtomatosaucecontainingACS-Kand/
orASPcanbeanalyzedwiththeuseofaFIAsetupcoupledwithanultraviolet(UV)detector.An
adequateamountofbeverageistaken,degassed,anddiluted,adjustingthesameconditionsasthe
carrier.Finally,itisilteredthrougha0.2-mmMilliporeilter.Fortheanalysisinjuicesbeforethe
stepofiltering,acentrifugestepmaybenecessary.Inthecaseofstrawberrysweets,anadequate
amountisweighedandthoroughlycrushedinaglassmortar,andthendissolvedinwaterwiththe
aidofanultrasonicbath,adjustingtothesameconditionsasthecarrier.Afterthat,itiscentrifuged
andilteredasabove.Finally,inthecaseoftomatosauce,theamountissuspendedinwater;then
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