Chemistry Reference
In-Depth Information
table 4.3 Simpler Methods for analysis of Food products for Nonnutritive Sweeteners
Cola, pudding,
chocolate
Saccharin, cyclamate,
alitame
μ Bondapak C-18
or Supelcosil
LC-18
Phosphate buffer
20 mM (pH 3.5)-
acetonitrile 97:3
Ri, uV,
200 nm
Candy, soft drinks,
yogurt, custard, fruit
juice, nectar, biscuit,
chocolate
Aspartame and its
decomposition
products, saccharin,
alitame, acesulfame-K
μ Bondapak C-18
Phosphate buffer
125 mM (pH 3.5)-
acetonitrile 90:10,
85:15, 98:2
uV, 220 nm
andamobilephaseofacetonitrile-0.0125Mpotassiumdihydrogenphosphate(10:90,v/v)atpH3.5
andUVdetectionat220nmhasbeenadvocated.Thismethodallowsforthesimultaneousdetermi-
nationoftheobromine,theophylline,caffeine,vanillin,dulcin,sorbicacid,saccharin,alitame,ASP,
and their degradation products in a single run of 60-min duration. Tabletop sweeteners, candies,
softdrinks,fruitjuices,fruitnectars,yogurts,creams,custards,chocolates,andbiscuitshavebeen
analyzedbysimpleextractionorjustbydilutionusingthismethod.
SomeofthesimplerLCmethodsforsweeteneranalysisaregiveninTable4.3.
4.15.3 Determination of aSp
A screening low-injection spectrophotometric method in tabletop sweeteners and in food
samples(pudding,gelatin,andrefreshment)usingninhydrinasacolorimetricreagentisreported.
Thereactionisconductedina1:1v/vmethanol-isopropanolmediumthatalsocontainspotassium
hydroxide.Theabsorbancemeasurementsaremadeat603nm.Theresultsobtainedforthedeter-
minationofASPhaveagoodcorrelationcoeficient:
r
=0.998.Thirty-sixsamplescanbeanalyzed
perhour,andtheRSDislessthan3.5%(
n
=6)forallsamples.Thedetectionlimitis0.0381mM
ofASP(Nobregaetal.1994).
Anotherlow-injectionspectrophotometricmethodisdevelopedfordeterminingASPintable-
topsweetenerswithoutinterferenceofsaccharin,ACS-K,andcyclamate.Samplesaredissolvedin
water,andaportionofthesolutionisinjectedintoacarrierstreamof5.0×10
−3
Msodiumborate
solution (pH 9.0). The sample low through a column packed with Cu
3
(PO
4
)
2
immobilized in a
matrixofpolyesterresin.ThenCu(II)ionsarereleasedfromthesolid-phasereactorbytheforma-
tionofCu(II)(ASP)
2
complex.Themixtureismergedwithastreamofboratebuffersolution(pH
9.0) containing 0.02%(w/w)alizarinredS, and theCu(II)-alizarin redcomplexformed ismea-
suredspectrophotometricallyat550nm.ThecalibrationgraphforASPislinearinthe20to80μg/
mLconcentrationrange,withadetectionlimitof2μg/mLofASP.TheRSDis0.2%forasolution
containing 40μg/mL ASP (
n
= 10), and 70 measurements are obtained per hour. The column is
stableforatleast8hofcontinuoususe(500injections)at25°C(Fatibello-Filhoetal.1999).
TheestablishmentofanalyticalconditionsforthedeterminationofASPbymeansofHPLC-
electrosprayionization-MS(HPLC-ESI-MS)hasbeenstudied.MSisapowerfulqualitativeand
quantitativeanalyticaltechniquethathasbeenintroducedinmanyanalyticalandresearchlabora-
toriesinthelast10years.ThecombinationofHPLCwithtandemMSyieldsaparticularlypower-
ful tool, and it is now the method of choice for analysis. However, HPLC-ESI-MS methods are
notcompletelywithoutproblemsthatcancompromisethequalityoftheresults.ASPisanalyzed
inthepositive-ionmodeat3.05-kVprobevoltagewithamethanol/watermobilephase(30:70,pH
3.00byadditionofaceticacid).Massspectraatdifferentsprayingcapillaryvoltagesarereported
anddiscussed.Adetectionlimitof5pgandalinearresponseforASPinaqueoussolutioninthe
rangeof1to200pgareobtained.ThemethodisappliedtothedetectionofASPinthreesoftdrinks
commerciallyavailableinItaly.HPLC-ESI-MSprovidesanadditionaltoolforthesensitiveand
selectivedetectionofASPandfortheimprovementofpossiblycriticalseparationssuchasthatof
ASPfromcaffeine(Gallettietal.1996).
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