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1、SpectrophotometricDeterminationofAmmonia-NitrogenAfterPreconcentrationasIndothymolonaGlass-FiberFilterinthePresenceofaCationicSurfactantAbstract:Ammonia-nitrogen,intherange0.06to2μgin20mlofwatersample,istreatedwithhypochloriteandthymoltoformanintenselyblueanionicdyecalledindothymo
2、l.Theindothymoliscollectedonaglass-fiberfilterastheion-pairwithbenzyldimethyltetradecylammoniumion.Theindothymolcol-lectedonthefilterisdissolvedinasmallvolumeofdimethylformamide(DMF)andtheabsorbanceduetotheindothymolismeasuredat675nmagainstthereagentblank.Anunexpectedlyhighensitiv
3、itywasobtainedbecauseoftheincreasedmolarabsorptivityofindothymolinDMF(3.2x1041mo1-1cm-1,λmax=675nm),pproximately3timeslargerthanthatinwater(1.16x1041mo1-1cm-1,λmax=660nm).Thedetectionlimit,definedasthreetimesthestandarddeviationoftheblank,isbetterthan1μg1-1ofammonia-nitrogenwith5-
4、foldpreconcentration.Keywords:ammonia-nitrogen,preconcentrationbyfilter,indothymol,spectrophotometry.Determinationofammonia-nitrogen,oneofthedecayproductsofnitrogenousorganiccompounds,isfrequentlyneededtoevaluatethedrinkingwatersafetyandenvironmentalpollution.Methodsforthedetermin
5、ationofammonia-nitrogenwerereviewedinapaperbySeale[1].Nessler'smethodwasusedatonetimeorthedeterminationofammonia-nitrogen,butthismethodlackssensitivityandhasaseriousdisadvantageofusingatoxicmercurycompound.Inrecentyears,methodsbasedonBerthelotreaction,thereactionbetweenammonia,chl
6、orineandphenoliccompoundstoformbluecompoundscalledindophenoldyes,havebecomemorewidelyused[2].AlthoughthemethodsbasedontheBerthelotreactionaremoresensitivethantheNesslermethod,theirsensitivitiesarenotsufficientforthedeterminationof#g1-1levelsofammonia-nitrogen.Wehaveproposedasimple
7、,rapidandversatilepreconcentrationtechnique,basedoncollectingtraceanalytesonasolvent-solublefilteranddissolvingthefilterandtheanalytescollectedonitinasmallvolumeofsolvent[-3-8].Theanalytesmayberetainedonthefiltermechanicallyorbysorption.Theanalytesintheconcentratearedeterminedspec
8、trophotometricallyorbyothermeans.
