美国药典USP32-重金属part-中文翻译

231HEAVYMETALSThistestisprovidedtodemonstratethatthecontentofmetallicimpuritiesthatarecoloredbysulfideion,underthespecifiedtestconditions,doesnotexceedtheHeavymetalslimitspecifiedintheindividualmonographinpercentage(byweight)ofleadinthetestsubstance,asdeterminedbyconcomitantvisualcomparison(seeVisualComparisoninthesectionProcedureunderSpectrophotometryandLight-Scattering851)withacontrolpreparedfromaStandardLeadSolution.[NOTE—Substancesthattypicallywillrespondtothistestarelead,mercury,bismuth,arsenic,antimony,tin,cadmium,silver,copper,andmolybdenum.]DeterminetheamountofheavymetalsbyMethodI,unlessotherwisespecifiedintheindividualmonograph.MethodIisusedforsubstancesthatyieldclear,colorlesspreparationsunderthespecifiedtestconditions.MethodIIisusedforsubstancesthatdonotyieldclear,colorlesspreparationsunderthetestconditionsspecifiedforMethodI,orforsubstancesthat,byvirtueoftheircomplexnature,interferewiththeprecipitationofmetalsbysulfideion,orforfixedandvolatileoils.MethodIII,awet-digestionmethod,isusedonlyinthosecaseswhereneitherMethodInorMethodIIcanbeusedSpecialReagentsLeadNitrateStockSolution—Dissolve159.8mgofleadnitratein100mLofwatertowhichhasbeenadded1mLofnitricacid,thendilutewithwaterto1000mL.Prepareandstorethissolutioninglasscontainersfreefromsolubleleadsalts.StandardLeadSolution—Onthedayofuse,dilute10.0mLofLeadNitrateStockSolutionwithwaterto100.0mL.EachmLofStandardLeadSolutioncontainstheequivalentof10µgoflead.Acomparisonsolutionpreparedonthebasisof100µLofStandardLeadSolutionpergofsubstancebeingtestedcontainstheequivalentof1partofleadpermillionpartsofsubstancebeingtested.MethodIpH3.5AcetateBuffer—Dissolve25.0gofammoniumacetatein25mLofwater,andadd38.0mLof6Nhydrochloricacid.Adjust,ifnecessary,with6Nammoniumhydroxideor6NhydrochloricacidtoapHof3.5,dilutewithwaterto100mL,andmix.StandardPreparation—Intoa50-mLcolor-comparisontubepipet2mLofStandardLeadSolution(20µgofPb),anddilutewithwaterto25mL.UsingapHmeterorshort-rangepHindicatorpaperasexternalindicator,adjustwith1Naceticacidor6NammoniumhydroxidetoapHbetween3.0and4.0,dilutewithwaterto40mL,andmix.TestPreparation—Intoa50-mLcolor-comparisontubeplace25mLofthesolutionpreparedforthetestasdirectedintheindividualmonograph;or,usingthedesignatedvolumeofacidwherespecifiedintheindividualmonograph,dissolveinanddilutewithwaterto25mLthequantity,ing,ofthesubstancetobetested,ascalculatedbytheformula:2.0/(1000L),inwhichListheHeavymetalslimit,asapercentage.UsingapHmeterorshort-rangepHindicatorpaperasexternalindicator,adjustwith1Naceticacidor6NammoniumhydroxidetoapHbetween3.0and4.0,dilutewithwaterto40mL,andmix.MonitorPreparation—Intoathird50-mLcolor-comparisontubeplace25mLofasolutionpreparedasdirectedforTestPreparation,andadd2.0mLofStandardLeadSolution.UsingapHmeterorshort-rangepHindicatorpaperasexternalindicator,adjustwith1Naceticacidor6NammoniumhydroxidetoapHbetween3.0and4.0,dilutewithwaterto40mL,andmix.Procedure—ToeachofthethreetubescontainingtheStandardPreparation,theTestPreparation,andtheMonitorPreparation,add2mLofpH3.5AcetateBuffer,thenadd1.2mLofthioacetamide–glycerinbaseTS,dilutewithwaterto50mL,mix,allowtostandfor2minutes,andviewdownwardoverawhitesurface*:thecolorofthesolutionfromtheTestPreparationisnotdarkerthanthatofthesolutionfromtheStandardPreparation,andthecolorofthesolutionfromtheMonitorPreparationisequaltoordarkerthanthatofthesolutionfromtheStandardPreparation.[NOTE—IfthecoloroftheMonitorPreparationislighterthanthatoftheStandardPreparation,useMethodIIinsteadofMethodIforthesubstancebeingtested.]MethodIINOTE—Thismethoddoesnotrecovermercury.pH3.5AcetateBuffer—PrepareasdirectedunderMethodI.StandardPreparation—Pipet4mLoftheStandardLeadSolutionintoasuitabletesttube,andadd10mLof6Nhydrochloricacid.TestPreparation—Useaquantity,ing,ofthesubstancetobetestedascalculatedbytheformula:4.0/(1000L),inwhichListheHeavymetalslimit,asapercentage.Transfertheweighedquantityofthesubstancetoasuitablecrucible,addsufficientsulfuricacidtowetthesubstance,andcarefullyigniteatalowtemperatureuntilthoroughlycharred.(Thecruciblemaybelooselycoveredwithasuitablelidduringthecharring.)Addtothecarbonizedmass2mLofnitricacidand5dropsofsulfuricacid,andheatcautiouslyuntilwhitefumesnolongerareevolved.Ignite,preferablyinamufflefurnace,at500to600,untilthecarboniscompletelyburnedoff(nolongerthan2hours).Ifcarbonremains,allowtheresiduetocool,addafewdropsofsulfuricacid,evaporate,andigniteagain.Cool,add5mLof6Nhydrochloricacid,cover,anddigestonasteambathfor10minutes.Cool,andquantitativelytransferthesolutiontoatesttube.Rinsethecruciblewithasecond5-mLportionof6Nhydrochloricacid,andtransfertherinsingtothetesttube.MonitorPreparation—Pipet4mLoftheStandardLeadSolutionintoacrucibleidenticaltothatusedfortheTestPreparationandcontainingaquantityofthesubstanceundertestthatisequalto10%oftheamountrequiredfortheTestPreparation.Evaporateonasteambathtodryness.Igniteatthesametime,inthesamemufflefurnace,andunderthesameconditionsusedfortheTestPreparation.Cool,add5mLof6Nhydrochloricacid,cover,anddigestonasteambathfor10minutes.Cool,andquant