Chemistry Reference
In-Depth Information
Analysis of liquid samples does not require the homogenization step because of their liquid
state.Aftersamplepreparation,somematrixcomponentsmaycoextractwithanalytesbecauseof
similarsolubilityinthesolventsusedforextraction,interferingintheanalysisandcausingprob-
lemswithmethodaccuracy.Furthercleaningupthesampleforanalysisistheonlywayofproblem
resolution.CleanupisusuallycarriedoutbySPE,dialysis,liquid-liquidextraction,precipitation,
andiltration.
Optimalsamplepreparation,extraction,cleanup,and/orpuriicationcanreduceanalysistime,
enhancesensitivity,andenableconirmationandquantiicationofanalytesanddependsonthecom-
plexityofthesampleandthesensitivityandselectivityofthemethodused(Self2005).
Determination of acesulfame K and aspartame in a simple matrix is much easier, less time
consuming,andlesscomplexthanthedeterminationofthesetwosweetenersinamorecomplicated
foodsamplematrix.Bulksamplesofsweetenershaveamuchmoresimplepretreatmentstagethan
complexfoodmatrices.Theinterferenceofotherfoodadditivesinthedeterminationofsweeten-
ersismorecommonincomplicatedfoodsamplematrices.Inbulksamples(e.g.,tabletoptablets),
additivesarepresentinmuchlowerquantities.Usually,threetypesofadditivesareaddedinbulk
powders: (1) glidants for a better low in the material; (2) pure lubricants for better mixing; and
(3)antiadherentsfornonadherenceofthetablettothedie.Determinationofsweetenersintable-
topsolidtabletsisdonebyconvertingthemintopowder,weighingthepowder,dissolvingitinto
ultrapurewater,andtransferringitintovolumetriclasks.Liquidsweetenersandbeverageswitha
relativelysimplematrixcanbedilutedordissolvedindeionizedwaterorinanappropriatebuffer.
Carbonateddrinkshavetobedegassedbysonication,spargingwithnitrogen,orundervacuum.
Prior to analysis, all samples are iltered, and extracts are centrifuged. SPE is used to pre-
concentratetheanalytesand/orremovethechemicalinterferences.ThemostfrequentlyusedSPE
cartridgesarenonpolarC
18
.TheirstationarypackingmaterialconsistsofnonpolarC
18
chains.The
SPEprocedureconsistsoffoursteps:(1)cartridgeconditioning;(2)sampleload;(3)cartridgewash;
and(4)elutionofanalytes.
ThetypeofSPEpackingmaterial,solvents,pH,andlowratesareveryimportant.Theinter-
fering substances should be retained very strongly, and weakly retained substances are readily
removedfromthecartridgeduringsampleloadand/orcartridgewash.Analytesareelutedduring
the elution step, and interfering substances having a strong afinity to the sorbent stay adsorbed
withinthecartridge.EvaporationoftheinalSPEextracttodrynessanditsreconstitutionwitha
smalleramountofasolvent(preconcentration)mightenhancethesensitivityofainaldetermina-
tion.SPE-basedsample-preparationprotocolsaresimple,reproducible,reasonablyquickandinex-
pensive,andcompatiblewiththemostpopulartechniquesusedinfoodanalysis(Tunick2005).
Currently, the most common technique for the determination of artiicial sweeteners in soft
drinksishigh-performanceliquidchromatography(HPLC).SamplepreparationforHPLCincludes
ilteringthrougha0.45-mmmembraneilter,followedbyultrasonication.Nectarsarecentrifuged,
iltered through membrane ilters, and then ultrasonicated (Lino, Costa, and Pena 2008). For the
determinationinacoladrink,thevolumeofthedrinkisaccuratelyweighedintoavolumetriclask
andthendegassedinanultrasonicbath.IfdeterminationiscarriedoutbyHPLC,thevolumeof
thecoladrinkisdirectlydilutedinamobilephase(Demiralay,Çubuk,andGuzel-Seydim2006).
Sweetened beverages include two types of beverages with carbon dioxide and two types of
beverages without carbon dioxide. Beverages with and without carbon dioxide include light and
sugar-sweetenedsoftdrinks.Inlightsoftdrinkswithcarbondioxide,amixtureofaspartameand
acesulfameKismoreoftenusedasasweetener(Leth,Fabricius,andFagt2007).Micellarelectro-
kineticcapillarychromatography(MEKC)isarapidmethodusedinthedeterminationofartiicial
sweeteners in low-calorie soft drinks. Low-calorie soft drinks are prepared by dilution with an
appropriateamountofdeionizedwater,followedbyilteringthrougha0.45-μmcelluloseacetate
ilterbeforeanalysis(Thompson,Trenerry,andKemmery1995a).
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