(5.4)-4.4原子吸收基本操作

4.4BasicOperationofAtomicAbsorptionSpectrophotometerAtomicabsorptionspectrometrymoduleofAbilityobjectiveBeabletouseatomabsorptionspectrophotometer,aircompressor,andacetylenesteelcylindercorrectly.Beabletotroubleshootsimpleinstrumentfaults.ProblemintroductionFoodnutritionandsafetyarethetwothemesmostcloselyrelatedtoeveryoneinmodernlife.Thepollutionpreventionoftraceelementsandheavymetalsisanimportantpartoffoodnutritionsafety,whichcannotbeseparatedfromtheworkofanalysisanddetection.Ifanexistingfoodsampleneedstobedeterminedwithtracemetalelements(suchasZn,Mg,Pb,Cu,etc.),thenwhatmethodcanbeused?Pleasetellusthemethodyouaremostfamiliar.Solution:Chemicalmethod,potentiometricmethodandUV-visiblespectrophotometricmethodcanbeused.Thesemethodshavetheirowncharacteristics.Thesensitivityofchemicalmethodisrelativelylow,whichmaybeinsufficientinthemeasurementoftraceelements.Theothertwomethodsareeasytobeinterferedbytheco-existingcomponentsinsolution.Atomicabsorptionspectroscopyisaverygoodmethodtosolvethiskindofproblem.AnalyticalprocessLightsource(emissionofcharacteristicspectrumline)→atomizer(sampleconversionintoatomicvapor)→spectroscopicsystem(separationofcharacteristicspectrumline)→detectionsystem(signalconversion,amplification,anddisplay)AtomicabsorptionspectroscopyisananalyticalmethodbasedontheabsorptionofcharacteristicradiationbyatomsLightsourceFlameatomizerEffluentoutletdetectionsystemspectroscopicsystemTestsolutionReadinginstructionInfrontofthestudentsaretheinstructionsfortheuseoftheatomicabsorptionspectrophotometer.Pleasereadtheinstrumentintroductionandoperationsectioncarefullytohaveabasicunderstandingoftheinstrument,andtoknowtheelectricalandpneumaticconnectionoftheinstrumentandthefunctionofeachfunctionbuttonbyreferringtotheactualobjectoftheinstrument.Turnonthepowersupply-----startthecomputer----installthehollowcathodelamp----startthemainengine----opentheoperationsoftware----initialization----peak-seeking----settheexperimentcondition----checkthedrainagesafetyinterlockdevice----opentheaircompressor(adjusttheoutletpressure0.25-0.03MPa)----opentheacetylenesteelcylinder(adjusttheoutletpressure0.05-0.07MPa)----opentheairoutlet----ignitefire----determinesample----savethedata----closeofftheacetylenesteelcylinderafterdetermination----closetheaircompressorafterflameextinguished----closetheairoutlet----withdrawsoftware----closethemainenginepowersupply----turnoffthecomputer----fillintheusingrecordofinstrument.InstrumentswitchandprocedureTurnonthepowersupplyInordertoensurethestabilityoftheinstrument'spowersupply,astabilizedpowersupplyisprovided.A.PresstheswitchontherearpanelofthestabilizedpowersupplylightlyB.Workinglighton,voltagedisplay220VBasicOperationDemonstration1StartthecomputerTAS990atomicabsorptionspectrophotometerisequippedwithmicrocomputersystemandhasspecialoperationsoftware.Firststartthecomputertoenterthewendousoperationsystembeforestartingup.BasicOperationDemonstration2AAWinV2.1workingsoftwareSelectthesamehollowcathodelampasthedeterminationelementtoalignthelampfoottofittheinsertion.Mountedhollowcathodelamp2.PuttheHCLlampintothelampchamberandrememberthepositionnumber.1.InserttheprojectingportionoftheHCLfootintothegrooveofthelampholder;3.Tightenthelampholderfixingscrew;4.Coverthelightchamberdoor.BasicOperationDemonstration3TurnonthepowersupplyBasicOperationDemonstration41.AdjusttherotationadjustingbuttonoftheburnerAdjusttheburnerandalignthelightpath3.Makethespotemittedfromthelightsourcedirectlyabovetheburningslitandparalleltotheburningslit.2.AdjustthefrontandrearadjustingbuttonoftheburnerBasicOperationDemonstration5InitializationTheuseofworkingsoftwareSelectionandpreheatingofhollowcathodelampSetelementconditionMeasurementBasicOperationDemonstration64.Openthesteelcylindermastervalvecounter-clockwise.5.Rotatethepressurereducingvalveclockwise.6.Adjustthepressureto0.05MPaGaspressureadjusting2.Rotatethepressureadjustingbuttonclockwise.1.Turnonthepowersourceswitch3.Adjustpressureto0.3MPaBasicOperationDemonstration7BranchpipeBCheckthewasteliquiddischargepipeandopentheairoutletPresstheairoutletswitch"ON"toturnontheairoutlet;Pourasmallamountofwaterintothedrainagesafetytanktoallowwatertoflowoutofthedrainpipe;Theairoutletisdischarged.BasicOperationDemonstration8IgnitionoperationClickthe“Ignition”buttonLightaflame.Note:Becausetherewillbeairintheacetylenepipelineiftheinstrumentisnotusedforalongtime,sothefirstignitionmaynotwork,butafewmoretimesoftryingwilldo.BasicOperationDemonstration9Sampleabsorbancemeasurement1.Insertthesamplecapillaryintothedistillingwater.Aftertheabsorbanceisstable,clickzerocalibration,andtheabsorbanceisshowntobezero.2.Liftthecapillaryandwipeoffthemoisturewiththefilterpaper.3.Insertthesamplesolution,readandrecordtheabsorbanceaftertheabsorbanceisstable.BasicOperationDemonstration10Shutdownoperation:1.Inhaledistilledwaterfor5min2.theacetylenemainvalveshouldbeclosed3.Fireshut-outandclosethepressurereducingvalve5.Closetheairoutlet4.Turnofftheaircompressor6.TurnoffthemainframepowerBasicOperationDemonstration11

SummaryofinstrumentoperationmethodSwitchonthepowerandturnonthecomputer;Installthehollowcathodelamp；TurnonthepowersupplyOpenoperationsoftware,andinitialize;Setexperimentalconditions,peakseeking;Checkthedrainagedevice;Openaircompressor,adjustoutletpressureis0.3MPa;Openacetylenesteelcylinder,adjustoutletpressureto0.05MPa;Ignition;Sampledetermination;Afterfinishingwork,turnoffinreverseorder,andfillintheusingrecordoftheinstrument.Whenigniting,opentheairfirst,thenopentheacetylene.Turnofftheacetylenebeforeclosingtheair.Whenpeakseekingiscompleted,thepositionoftheburnerissometimesneededadjustmentbeforeignition,sothatthelightemittedbythehollowcathodelampisparalleltoanddirectlyabovetheburningslit.Unlikenitrogen,airandoxygensteelcylinders,acetylenesteelcylindersarefilledwithactivatedcarbonandacetone,withacetylenedissolvedinacetone,cannotbecompletelyused,andmustbesetaside0.5MPa,otherwiseacetylenewillvolatilizeintotheflamewiththebackgroundincreasedandburninginstability.Theinstrumentshouldhavegoodgroundingwhenconnectedtothepowersupply.Atomabsorptionanalysisoftencontactswithelectricalequipment,high-pressuresteelcylinders,andtheuseofopenfire,soweshouldalwayspayattentiontosafety,masterthenecessaryelectricalknowledge,firstaidknowledge,andfireextinguisherusingmethod.Cautionsforoperation1Afterinstallingthehollowcathodelamp,thelampchamberdoorshouldbeclosed.Youshouldnotputyourhandsintothelampchamberwhilethelampisturning.Whenpressingtheignitionbutton,makesurethatotherpersonnel'shandsandfacearenotabovetheburningchamber,andthecombustionchambershieldisbetterclosed.Donotplaceanythingonaflameoruseitforotherpurposes.Donottouchtheburnerbyhandduringburning.Itisbesttoclosethechambershieldduringthedetermination.High-temperatureflamemayproduceultravioletlightandburnpeople'seyes.Aftertheflameisextinguished,theburnerisstillhot,soyoushouldnottouchitwithin20minutes.Cautionsforoperation2Intheprocessoftest,ifemergenciessuchasgasleakageandpowerfailurehappen,youshouldfirstpresstheemergencyfirestopswitch,shuttheacetylenesteelcylindergeneralvalve,openthelaboratorywindow,checkthecauseoftheaccident,andrestartafterthecauseeliminationofemergency.Acompletesafetyprotectiondeviceisarrangedinsidetheinstrument,whichincludesagasleakagealarm(thealarmwillbesoundedwhenthegasisleaking),airpressuredetection(whentheairpressureislessthan2.0bar,theinstrumentwillalarm),liquidleveldetectionofwasteliquid,andflameconditionmonitoring.Onlywhenallthesafetydevicesareinnormalconditioncantheinstrumentbeignitedformeasurement.Anyabnormalsituationmaycausetheflametoextinguishandprovideanalarmsignal.Emergencysettlementprocedures

Practicetheoperationoftheatomicabsorptionspectrophotometeraccordingtotheabovedemonstration.Theexperimentalconditionsaresetaccordingtothefollowingparametersandtheabsorbanceofthesolutionofρ（Mg)＝0.3µg/mLismeasuredLightsource:magnesiumhollowcathodelamp;Analysisline:285.2nm;Lampcurrent:2mA;Burnerheight:6mm;Spectralpassband:0.4nm;Gasflowrate:2000mL/min.StudentpracticaltrainingoperationFailurephenomenonPossibleReasonSolutionNopowersupplyoftheinstrument1.Thereisnopowersupplyintheroom;2.Thepowerplugfallsoffandloosens;3.Theinstrumentfusehasblown.Checkeverylinkinthecircuitandreplacethefuse.Medium-wavelengthmotorappears"×"intheprocessofinitialization1.Checkwhetherthehollowcathodelampisinstalledandlit;2.Objectsinthelightpathblockthelight;3.Thehostandcomputercommunicationsystemaredisconnected.1.Reinstallthelamp;2.Removethelightblockingobjectinthelightpath;3.Restarttheinstrument.Elementlightisnoton1.Checkwhetherthelamppowerlineisoff-welding;2.Thelampsocketisloose;3.Hollowcathodelampisdamaged.1.Reinstallthehollowcathodelamp;2.Replacethelamppositionandreinstall;3.Tryanotherlamp.Theenergyistoolowortheenergyisabovetheupperlimitinpeak-seeking1.Elementlightisnoton;2.Theelementlamppositionisnotcorrect;3.Errorinlineselection;4.Thereisalightblockingobjectinthelightpath;5.Lampaging,lowemissionintensity1.Reinstallthehollowcathodelamp;2.Re-setthelampposition;3.Choosethemostsensitiveline;4.Removethelightshield;5.Replacenewlamp.CommonfaultandtroubleshootingClickthe"ignition"button,theigniterhasnohigh-voltagedischargeignition1.Thereisnopressureorinsufficientpressureintheair;2.Acetyleneisunopenedorunderpressure.3.Theliquidlevelofliquidwasteistoolow;4.Theemergencyfire-extinguishingswitchislit;5.Acetyleneleakage,alarm.6.Thereisstronglightshiningontheflameprobe.1.Checktheoutletpressureoftheaircompressor;2.Checktheoutletpressureofacetylene;3.Pourthedistilledwaterintothewasteliquiddischargesafetyinterlockdevice;4.Extinguishthefirebypressinganemergencyfire-extinguishingswitch;5.Closeacetylene,checkpiping,opendoorsandwindows.6.Removethelightshield;Clickthe"ignition"button,theigniterhasahigh-voltagedischargeignition,buttheburnerflamecannotbeignited1.Acetyleneisunopenedorunderpressure.2.Ifthepipeistoolong,theacetylenehasnotenteredtheinstrument;3..Thereisstronglightshiningontheflameprobe4.Unsuitablefuelgasflow;1.2.Checkandadjustacetylenepressuretonormalvalue;repeatignitionformultipletimes.3.Blockthestronglightontheflameprobe;4.Adjustthefuelgasflow.TestBaselineUnstable,BigNoise1.Theinstrumentenergyislowandthenegativehighvoltageofthephotomultiplieristoohigh;2.Inaccuracyofwavelength;3.Unstableemissionofelementlamp;4.Unstableexternalvoltageandvibrationofthetable.1.Checkwhetherthelampcurrentissuitable,ifnot,reset;2.Checkwhetherthepeakseekingisnormal,ifnot,restartpeakseeking;3.Trytoreplacetheknownlamps;4.Checkthestabilizedpowersupplytoensureitsnormaloperation,removethevibrationsource.CommonfaultandtroubleshootingLowornoabsorbanceduringtesting1.Theburningslitisnotalignedwiththelightpath;2.Theheightofburnerisnotappropriate;3.Theflowrateofacetyleneisnotsuitable;4.Theanalysiswavelengthisnotcorrect;5.Energyvaluesareloworsaturated;6.Thesuctioncapillaryisblocked,andtheatomizerdoesnotspray;7.Thesamplecontentistoolow.1.Adjusttheburner;2.Raisetheheightoftheburner;3.Adjusttheflowrateofacetylene;4.Checkandadjusttheanalysiswavelength;5.Carryoutenergybalance;6.Removeandcleanthecapillarytube;7.Re-processthesample.Flameinstabilityduringtesting1.Theoutletpressureofaircompressorisunstable;2.Theacetylenepressureisverylowandtheflowrateisunstable.3.Therearesaltcrystalsintheburningslit,andtheflameisserrated;4.Thereiswindaroundtheinstrument.1.Checkthepressuregaugeoftheaircompressor;2Replaceacetylenesteelcylinders;3.Cleantheburner;4.Opentheairoutletandclosethedoorsandwindows.Whenclickingthecomputerfunctionkey,theinstrumentdoesnotexecutethecommand1.Thecomputerandthehostareinthestateofofflineworking;2.Thehostisnotfinishedexecutingothercommands;3.Thecommunicationcableisloose.4.Computeriscrashed,andthereisvirusattack.1.Restart;2.Closeothercommandsorwait;3.Reconnectthecommunicationcable;4.Restartthecomputer.CommonfaultandtroubleshootingStructureofinstrumentLightsourceAtomizationsystemCheckingsystemSpectroscopicSystemLightsourceFunction:producethecharacteristicradiationneededforatomicabsorption.Requirements:sharplinelightsource;stronglight;stable;smallbackground;longservicelife;cheapprice.Type:hollowcathodelamp,non-polardischargelamp,vapordischargelamp,lasersourcelamp.HollowcathodelampElectrodelessdischargelampRadio-frequencycoilCeramicframeLamp

Appearance:lampfoot,glasstube,quartzlightwindow;Cathode:Metalsoralloystobemeasured;HollowcathodelampstructureAnode:Titaniumwireortantalumsheetontungstenrod;ThetubeisfilledwithseveralhundredPaoflow-pressureinertgases.(neonorargon)QuartzlightthroughwindowCathodeFastfillinggasGlasspipeAnodeLampfootVoltageaddingbetweentwopolesGasglowdischargeGasionizationCationicimpingingcathodeFreeatomsputteringAtomicexcitationEmissionofcharacteristiclineTheworkingprincipleofhollowcathodelampPictureexampleLightquantumMetal-coppergroundstateatomExcitedstatecopperatomElectronResonanceemissionlineofcopperHCLoperationparameters:lampcurrent.Inordertoobtainstableandhigh-intensitynarrow-linespectrum,thehollowcathodelampusuallyadoptspulsepowersupplymode,andthelampcurrentisintheaveragevalueofpulsesignal.Thelampcurrentisusuallysetat1~20mA.Differentelementslampswillchoosetheappropriatelampcurrentaccordingtoneeds.Iftheelectriccurrentofthelampistoosmall,thedischargewillbenotstable;Iftheelectriccurrentofthelampistoolarge,thesputteringeffectwillbeincreased,theatomicvapordensitywillbeincreased,thespectrumlinewillbebroadened,theself-absorptionmayevenbecaused,thedeterminationsensitivitywillbedecreased,thelamplifewillbeshorten.LampcurrentsettingThehollowcathodelampshouldbepreheatedfor20min~30minbeforeusing.Afterigniting,whetherthelampisworkingproperlycanbejudgedbythecolorofthecathodeglow;(neonisinorange;argonisinlavender;mercurylampisinblue.Whenthereareimpuritiesinthelampgas,negativeglowcolorwillgetlight,suchasneonfillingcanturnthelightcolorintopink,blueorwhite,andthat’swhenthelightshouldbetreated.)Iftheelementlampisnotusedforalongtime,regular(everymonthoreverytwo,threemonths)igniteprocessingshouldbecarriedout,thatis,toigniteforonehourintheworkcurrent.Ifthereareimpuritiesinthelampgasandabnormalglowing,reverseconnectioncanbecarriedout.Whenusingelementlamp,itshouldbetakenandputlightly.Afterusinglow-melting-pointlights,theyshouldnotbemoveduntiltheyarecooled.Inordertomaketheemissionintensityofhollowcathodelampstable,thehollowcathodelampcrystalwindowshouldbekeptclean,andthelamproomcovershouldbecoveredwellafterlighting.HollowCathodeLampUsageFunction:Toconverttheelementtobemeasuredinasampleintoagaseousground-stateatom.Type:Flameatomizer;Flame-freeatomizer.FlameatomizerAtomizerBurnerPremixingchamberFlame-free(electricallyheated)atomizerAtomizationsystemConnectingcombustion-supportinggas/fuelgasIgnitionaftermixingofthepremixingchamberAfterthesampleisatomized,itenterstheflameandproducesanatomicvaporWorkingprincipleofflameatomizerAirorN2O1.Flame2.Burner3.Impactball4.Capillary5.Atomizer6.Testsolution7.Wasteliquid8.Pre-mixingchamberAirorN2OAir-acetyleneflame:Itstemperaturecanreach2300℃,andit’smostcommonlyusedandsuitablefordeterminationofmostelements.N2O-acetyleneflame:Itstemperaturecanreachupto3000℃.Ithasreducibilityandissuitableforthedeterminationofrefractoryoxideelements.Hydrogen-AirFlame:Ithaslowtemperature,smallbackground,andit’ssuitableforanalysisofelementsbelow200nm(e.g.As,Se.).Importantcharacteristicsofflame:1.Temperature2.Oxidativereduction.FrequentlyusedflameFlameatomizationprocessspayingMixeddehydrationAsmalldropoffogenterstheflameMeltevaporationPyrolytic(Atomicgas)reduction(wasteliquiddischarge)Largemistdroplet(Air)(solution)(FogDrop)FogdropseparationSolidmatterparticlesDryingatomizingFlameatomizationiswidelyusedbecauseofitseasyoperation,goodreproducibilitylargeeffectiveopticalpath,andhighsensitivityformostelementsHowever,theflameatomizationmethodhaslowatomizationefficiencyandinsufficientsensitivity,andcannotanalyzesolidsamplesdirectly.CharacteristicsofflameatomizationElectrothermalatomizerisalsocalledgraphitefurnaceatomizer.Thecharacteristicsofelectrothermalatomization:hightemperature,highsensitivity,lowsampledosage,theabilitytodirectlydeterminesolidsamples.6mm4mm30mmGraphiteTubeElectrothermalatomizationLightemittedbyalightsourceisreflectedtothegratingbyanincidentslit-concavemirrorThegratingisthenfocusedontheexitslitbyaconcavemirrorafterspectroscopy.RotatethegratingtoselectthedesiredabsorptionlineWorkingprincipleofspectroscopicsystemItrequiresresolutionof0.3nmandcandistinguishthetwolinesofMn279.5nman