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1、SpectrophotometricDeterminationofAmmonia-NitrogenAfterPreconcentrationasIndothymolonaGlass-FiberFilterinthePresenceofaCationicSurfactantAbstract:Ammonia-nitrogen,intherange0.06to2μgin20mlofwatersample,istreatedwithhypochloriteandthymoltoformanintenselyblueanionicdyecalledindothymol.Theindothymolis
2、collectedonaglass-fiberfilterastheion-pairwithbenzyldimethyltetradecylammoniumion.Theindothymolcol-lectedonthefilterisdissolvedinasmallvolumeofdimethylformamide(DMF)andtheabsorbanceduetotheindothymolismeasuredat675nmagainstthereagentblank.Anunexpectedlyhighensitivitywasobtainedbecauseoftheincrease
3、dmolarabsorptivityofindothymolinDMF(3.2x1041mo1-1cm-1,λmax=675nm),pproximately3timeslargerthanthatinwater(1.16x1041mo1-1cm-1,λmax=660nm).Thedetectionlimit,definedasthreetimesthestandarddeviationoftheblank,isbetterthan1μg1-1ofammonia-nitrogenwith5-foldpreconcentration.Keywords:ammonia-nitrogen,prec
4、oncentrationbyfilter,indothymol,spectrophotometry.Determinationofammonia-nitrogen,oneofthedecayproductsofnitrogenousorganiccompounds,isfrequentlyneededtoevaluatethedrinkingwatersafetyandenvironmentalpollution.Methodsforthedeterminationofammonia-nitrogenwerereviewedinapaperbySeale[1].Nessler'smetho
5、dwasusedatonetimeorthedeterminationofammonia-nitrogen,butthismethodlackssensitivityandhasaseriousdisadvantageofusingatoxicmercurycompound.Inrecentyears,methodsbasedonBerthelotreaction,thereactionbetweenammonia,chlorineandphenoliccompoundstoformbluecompoundscalledindophenoldyes,havebecomemorewidely
6、used[2].AlthoughthemethodsbasedontheBerthelotreactionaremoresensitivethantheNesslermethod,theirsensitivitiesarenotsufficientforthedeterminationof#g1-1levelsofammonia-nitrogen.Wehaveproposedasimple,rapidandversatilepreconcentrationtechnique,basedoncollectingtraceanalytesonasolvent-solublefilterandd
7、issolvingthefilterandtheanalytescollectedonitinasmallvolumeofsolvent[-3-8].Theanalytesmayberetainedonthefiltermechanicallyorbysorption.Theanalytesintheconcentratearedeterminedspectrophotometricallyorbyothermeans.
