Chemistry Reference
In-Depth Information
preparativeoperationsarelikelynecessarybeforeanextractioncanbeperformed.Fortheextrac-
tionofsweeteners,theseoperationsthatmakethecompleteextractioneasierareusuallythechange
ofvolumeandthechangeofpHpriortoextraction.
Foodsamplesarecharacterizedasdificultmatrices.Thefoodmatrixpresentsagreatvariability
in its composition. Carbohydrates, proteins, lipids, minerals, preservatives, colors, thickeners, and
vitamins may stand alone or coexist in a food matrix. All of the components can interfere in the
determinationofsweeteners.Samplepretreatmentproceduresmustbesuitablewiththemethodthat
theanalystwilluse,consideringtheinstrumentationthatheorshehasavailableinthelaboratory.The
successofthemethodisoftentotallyowedtotheeffectivenessofsamplepretreatment,anditdepends
ontheaccuracy(quantitativeor/andqualitative)thattheanalystwantstoobtain(“itforpurpose”).
Thechemicalandthephysicalpropertiesoffoodvary.Thevariabilityincompositionofagiven
food sample can be minimized with proper sample preparation. Generally speaking, preparation
offoodsamplesisachievedinfoursteps:(1)homogenization,(2)extraction,(3)cleanup,and(4)
preconcentration.
Analysis of liquid samples does not require the homogenization step because of their liquid
state.Afterthesamplepreparation,somematrixcomponentsmaystillbepresentinterferinginthe
analysis.Theymaycoextractwithanalytesduetosimilarsolubilityinthesolventsusedforextrac-
tion. The presence of matrix interferences in a sample extract can contribute to problems on the
accuracyofthemethod.Theonlywaytoresolvethisproblemistofurthercleanupthesamplefor
analysis.Cleanupisachievedcommonlyby(1)solid-phaseextraction(SPE),(2)dialysis,(3)liquid-
liquidextraction(LLE),(4)precipitation,and(5)iltration.
Appropriate extraction and cleanup procedures maximize recovery of the analytes. Optimal
sample preparation can reduce analysis time, enhance sensitivity, and enable conirmation and
quantiicationofanalytes.Extraction,cleanup,and/orpuriicationmightbenecessary,depending
onthecomplexityofthesampleandthesensitivityandselectivityofthemethodused(Self2005).
TheapproachofdeterminationofACS-KandASPinasimplematrixismucheasierandless
timeconsumingthanthedeterminationofthesetwosweetenersinamorecomplicatedfoodsample
matrix.Bulksamplesofsweetenershaveamuchmoresimplepretreatmentstagethancomplexfood
matrices.Theinterferenceofotherfoodadditivesinthedeterminationofsweetenersismorecom-
moninacomplicatedfoodsamplematrix.Theseadditivesmaybeinthesamelevelofmagnitude
asthesweetenersorinamuchhigherlevelofmagnitudecausinginterferenceinthedetermination.
In bulk samples (e.g., tabletop solid tablets), additive compounds exist in a much lower quantity.
Usuallythreetypesofadditivesareaddedinbulkpowdersinordertodealwithpossibleproblems
during the preparation of tablets. Glidants are added for dealing with a poorly lowing material.
Purelubricantsgivemoreeffectivemixing,andantiadherentspreventthetabletadheringtothedie.
Whenwewanttodeterminesweetenersintabletopsolidtablets,theseareturnedintopowder.A
portionofthepowderisbeingweighed,directlydissolvedinultrapurewater,andtransferredinto
volumetriclasks.Thenaccordingtothemethodsprotocol,thenextstepsofdeterminingACS-K
or/andASPfollow.Samplescharacterizedbyarelativelysimplematrix,likeliquidsweetenersand
beverages,cansimplybedilutedordissolvedindeionizedwaterorinanappropriatebuffer.Inthe
caseofcarbonateddrinks,thesampleshavetobedegassed.Degassingisbeingdonebysonication,
byspargingwithnitrogen,orundervacuum.
All samples are iltered prior to the analysis, and the extracts may need centrifugation. This
simplesamplepreparationprocedureisfoundinpublishedprocedures.Itisveryquickandcheap.
Topreconcentratetheanalytesor/andremovethechemicalinterferences,wemusttakeadvantageof
theSPEtechnique.Itfractionsthecompoundsofourchoicebasedontheafinityofthecompound
oragroupofcompoundstothestationaryphase.ThemostfrequentlyusedSPEcartridgesarethe
nonpolarC
18
.TheirstationarypackingmaterialconsistsofnonpolarC
18
chains.Theprotocolofan
SPEprocedureconsistsoffoursteps:(1)cartridgeconditioning,(2)sampleload,(3)cartridgewash,
and(4)elutionofanalytes.
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