OPTIMISATION DE L’INTERFACE DE COUPLAGE LC-ICP-MS/MS
A. CHOIX DU SYSTEME D’INTRODUCTION
Cette partie fait l’objet d’une publication publiée dans Journal of Chromatography (JCA)
“Suitable interface for coupling liquid chromatography to inductively coupled plasma-mass spectrometry for the analysis of organic matrices. 2 Comparison of Sample Introduction Systems”
M. Bernardin, F. Bessueille-Barbier, A. Le Masle, C.-P. Lienemann, S. Heinisch, J. Chromatogr. A. (2019), 380-387, doi.org/10.1016/j.chroma.2019.04.074
ContentslistsavailableatScienceDirect
JournalofChromatography A
j ou rn a l h om ep a ge :w w w . e l s e v i e r . c o m / l o c a t e / c h r o m a
Suitableinterface forcouplingliquid chromatographytoinductively
coupledplasma-massspectrometryfor theanalysisoforganic
matrices.2 ComparisonofSample IntroductionSystems
MarieBernardina,b,FrédériqueBessueille-Barbiera,AgnèsLeMasleb, Charles-PhilippeLienemannb,SabineHeinischa,∗
aUniversitédeLyon,InstitutdesSciencesAnalytiques,UMR5280,CNRS,ENSLyon,5ruedelaDoua,69100Villeurbanne,France
bIFPEnergiesnouvelles,Rond-pointdel’échangeurdeSolaize,BP3,69360Solaize,France
a r t i c l e i n f o
Articlehistory:
Received27February2019
Receivedinrevisedform29April2019 Accepted30April2019
Availableonline1May2019 Keywords:
Speciation
Ultrahighperformanceliquid chromatography
Inductivelycoupledplasma Extra-columndispersion Sampleintroductionsystem LC-ICP-MS
a b s t r a c t
Liquidchromatography(LC)coupledwithaspecificdetectionsuchasinductivelycoupledplasma-mass spectrometry(ICP-MS/MS)isatechniqueofchoiceforelementaryspeciationanalysisforcomplex matri-ces.Theanalysisoforganicmatricesrequirestheintroductionofvolatilesolventsintotheplasmawhich isananalyticalchallengeforthiscouplingtechnique.Detectionsensitivitycanbesignificantlyaffected byinstrumentallimitations.Amongthose,wewereinterestedinthesolutedispersionintotheinterface locatedbetweenLCandICP-MS/MS.ThisinterfaceconsistsinbothaSampleIntroductionSystem(SIS) andapossibleflowsplitter.Thisstudy,dividedintotwoparts,investigatedtheanalyticalperformance (intermsofsensitivityandefficiency)generatedbythecouplingofLCandICP-MSinthespecificcase oforganicmatrices.InPartI[1],wepreviouslydiscussedtheimpactofextracolumndispersiononthe performanceofLC-ICP-MS,firstfromatheoreticalpointofviewandnext,byassessingextra-column dis-persionin55publishedstudiesonLC-ICP-MS.ItwasshownthatSISwasrarelyoptimizedwithrespectto itscontributiontoextra-columnbandbroadening.Thecriticalimpactofflowsplittingonextra-column dispersionwasalsopointedout.
ThepresentPartIIisdedicatedtotheexperimentalcomparisonofcommerciallyavailableSISby assess-ingextra-columnbandbroadeningandhencethecontributionofSIStothelossinbothefficiencyand sensitivity.Itisshownthatthepeakvariance,duetoSIS,canvaryfrom10to8000L2dependingon thecombinationofbothnebulizerandspraychamber.Whereasthehighestvalues(i.e.>2000L2)are muchtoohighinhighperformanceliquidchromatography(HPLC),eventhelowestvalues(i.e.<100 L2)canbeinappropriateinultra-highpressureliquidchromatography(UHPLC)ashighlightedinthis study.Inlightoftheseresults,itappearsthatnebulizerandspraychamberhavetobechosentogether withrespecttothechromatographictechnique(HPLCorUHPLC)andthatbothpeakdispersionandpeak intensitydependonkeyparametersincludingSISdevicegeometry,flowrateenteringtheinterfaceor spraychambertemperature.
©2019ElsevierB.V.Allrightsreserved.
1. Introduction
LiquidChromatography(LC)hyphenatedtoaspecificdetection such as Inductively Coupled Plasma-Mass Spectrometry (ICP-MS/MS) iswidely usedto obtainelementalinformation and to discriminatespeciesinagivenmatrix[2,3].ReversedPhaseLiquid Chromatography(RPLC)[4] andSize-ExclusionChromatography (SEC)[5,6]bothperformedwithlargeamountsoforganicsolvent
∗ Correspondingauthor.
E-mailaddress:1sabine.heinisch@univ-lyon1.f(S.Heinisch).
inthemobilephasearegaininginterest,aspreviouslydiscussedin PartI.Overthepastfewyears,LCtechniqueshavebeenextensively usedforspeciationanalysis,inparticularwithnarrowbore(2.1mm i.d.)ormicrobore(1mmi.d.)columns,packedwithsmall parti-cles(sub2m)andoperatedunderultra-highpressure(UHPLC)in ordertoobtainhighcolumnplatenumberswithinshortanalysis times[7].InUHPLC(i.e.2.1mmi.d.columnpackedwithsub-2m particles),theoptimalflow-rateisusuallylowerthanin conven-tionalHPLC(i.e.4.6mmi.d.columnpackedwith5mparticles), whichisadvantageouswhenusingorganicsolventinICP-MS.If theflowrateenteringtheplasmasourceisdecreased,theamount oforganicsolventisalsodecreased,therebyimprovingtheplasma
https://doi.org/10.1016/j.chroma.2019.04.074
Table1
Nebulizercharacteristicsandsettings.
Nebulizer Design Supplier Rawmaterial Tubinglength Volume(L) TubingI.D.
MicroMist(Ezyfit) Microconcentric Agilent Borosilicate 2.3cm 6L 250m
PFA-LC Microconcentric GlassExpansion PFA Notubing 2L 150m
Opalmist Microconcentric GlassExpansion PFA 26.5cm / 180m
Savillex(C-Flow200) Microconcentric Savillex PFA 70cm / /
Burgener(T2002) Parallelpath Spectro Teflon 75cm 108L 380m
Crossflow Crossflow Spectro / / / /
I.D.forinternaldiameter.
Table2
Spraychambercharacteristicsandsettings.
Spraychamber Design Rawmaterial Volume(mL) Temperaturecontrol Specificity
Twinnabar Cyclonic Borosilicate 20 No Presenceofbaffle
IsoMist(Twinnabar) Cyclonic Borosilicate 20 Yes Presenceofbaffle
Totalconsumption Singlepass Quartz 22 No Nodrain
Impactbead(ConicalSprayChamber) Impactbead Borosilicate 27 No /
Agilent8800 Doublepass Quartz 70 Yes /
SpectroLarge Doublepass Borosilicate 150 No /
SpectroSmall Doublepass Borosilicate 75 No /
SinglePass Singlepass Borosilicate 75 No /
PC3 Cyclonic Quartz 47 Yes /
stability[8].Somekeyissueshavetobeconsideredforcoupling LCtoICP-MSin caseof organicmatrices.Thoseare thoroughly detailedinthefirstpartofthisstudy[1].Theinterfacebetween LCandICP-MSismadeofaSampleIntroductionSystem(SIS)anda possibleflowsplitterpriortotheSISwhichmayberequiredincase oforganicmatrices,toreducetheamountoforganicsolvent reach-ingtheplasma[8].AshighlightedinPartI,variousSIShavebeen usedoverthepastdecadesforthespeciationanalysisoforganic matricesbutsuitablechoiceswerenotalwaysmade.Moreover,our previousstudyclearlyshowedthatusingflowsplittingtoreduce theflow-rateenteringSISoranydetectiondevicecouldresultina significantincreaseinbandbroadening,especiallywhenthesplit ratioislow.
Thesuccessofhighlyefficientseparationsdependsonboththe intrinsiccolumnefficiencyandtheabilitytopreserveitby min-imizingextra-columnbandbroadening[9].Inordertomaintain columnefficiency,itisofprimeimportancetoreduceextra-column bandbroadeningineachdeviceoftheLC-ICP-MSinstrumentandin particular,intheinterfacepriortoICP-MS.Thisissueisespecially criticalincaseofUHPLCseparationsbecauseoflowpeakvolumes. Forcomplexsamples,on-linetwo-dimensionalliquid chromatog-raphy(2D-LC)isknowntobeapowerfulseparationtechnique[10]. However,duetotheextremethinnessofseconddimensionpeaks, thesuccessofthis techniquestronglydependsonthereduction ofthevolumeslocatedbetweentheseconddimensioncolumnand thedetector[9].Consideringsolutedispersion,theaimofthisstudy was tocompare commercially available devices (six nebulizers alongwithninespraychambers)andtheirresultingcombinations (i.e.31)thataremostcommonlyused[1].Somerecommendations for aproperselectionof bothnebulizer andspray chamberare providedasaresultofthisstudy.
2. Experimentalsection
2.1. ICP-MS/MSinstrumentandconditions
AsshowninPartI,alargepanelofnebulizersandspray cham-berscanbefoundintheliterature,withdifferentdesigns.Inthis work,concentric, parallel path, and cross-flownebulizerswere comparedandevaluated,aswellas,severalspraychambers,such assinglepass,doublepass,impactbead,cyclonic.Theexperiments werecarriedoutusinganAgilent8800ICP-MS/MSsystem (Agi-lentTechnologies).Forthepurposeofthestudy,31differentSIS
configurations,eachcomposedofonenebulizer(among6)anda spraychamber(among9)weretested.Among54possible com-binations,31wereachievablefromaninstrumentalpointofview (somenebulizerscannotbemountedoneveryspraychamberdue toinstrumentationissues).Adescriptionofthesixnebulizersand theninespraychambersaregiveninTables1and2respectively.
InTable1,tubinglengthandtubinginternaldiameter(i.d)
corre-spondtothedimensionsofthetubinglocatedbetweenthecolumn outletandthenebulizerentrance.Nebulizerswereusedintheir originalconfiguration,withoutanymodification.Ontheotherside, some spray chamberswere equippedwith a temperature con-trolleddeviceandsomeofthemwereequippedwithabaffleas highlightedinTable2.
Theinstrument wasequippedwitha torchwitha 1mmi.d. injector(AgilentTechnologies).Theanalyzerunitconsistsoftwo quadrupolemassanalyzersandanoctopolecollision-reactioncell placed between both quadrupoles. Vanadium was detected in MS/MSmodewithoxygenasareactiongasinthecell.Vanadium 51wasshiftedtomass67.ThefollowingICP-MS/MSparameters wereused:plasmapower:1500W,auxiliarygas:0.9L/min,plasma gasflow rate:15L/min. Bothsamplerand skimmerconeswere madewithplatinuminsteadofnickelasusual,duetoplatinum inertness.Theexperimentalconditionsforthe31 tested combi-nationsofanebulizerandaspraychamberarelistedinTable3. For parameteroptimization,a tunesolution(1ppbLi, Y,Tl,Ce, Co)wascontinuouslydeliveredtothenebulizerusingaperistaltic pumpequippedwithViton®tubingdedicatedtoorganicsolvents ataspeedof0.1rps(correspondingtoaflowrateof400L/min) exceptfortotalconsumptionspraychamber(i.e.0.05rps equiva-lentto200L/min).Fortransientsignal,theintegrationtimewas setat0.1s. ICP-MS/MSparameterswere optimizedtohave the besttrade-offbetweenahighintensityforstandardsolutionsof lithium,yttrium,andthalliumat1ppblevelandalowoxideratio. Theratio156CeO+/140Ce+wasusedtomonitortheoxideratiolevel which shouldideallybekeptbelow10% incase oforganic sol-vent. Theplasma gasflow rate,theauxiliary gasflow rate,the radio-frequency power, and the radiofrequencymatching were keptconstantforallstudiedcombinationsofnebulizersandspray chambers.Thecarriergasflowrate,thesamplingdepth,andthe optionalgasflowratewereoptimizedtoachievethehigher inten-sity(cps)forLi,Y,andTl.Inordertoensureastableplasmaandto avoidcarbondepositontheconesurface(samplerandskimmer), oxygenwasmixedwithargon(20%ofO2inAr)andcarriedto
ICP-Table3
Listofthe31studiedcombinationsofnebulizersandspraychambersandtheircorrespondingoperatingconditions.
# Spraychamber Nebulizer Carriergasflowrate(L/min) Spraychambertemperature Optionalgas(%)(20%O2inAr) Samplingdepth(mm)
1 IsoMist(Twinnabar) PFA-LC 0.8 −2◦C 27 9
2 Twinnabar Micromist 0.6 Notcontrolled 40 5 3 PFA-LC 0.6 40 6 4 Burgener 0.55 4 6 5 Opalmist 0.35 45 5 6 Savillex 0.4 45 5 7 Agilent8800 Micromist 0.75 2◦C 23 4 8 PFA-LC 0.55 Notcontrolled 20 5 9 Crossflow 0.75 25 3 10 Burgener 0.3 20 4 11
Impactbead(Conical SprayChamber) Micromist 0.65 35 6 12 PFA-LC 0.6 35 5 13 Burgener 0.55 35 4 14 Opalmist 0.55 35 5 15 SpectroLarge Micromist 0.9 45 5 16 PFA-LC 0.85 45 6 17 Burgener 0.7 40 6 18 Crossflow 0.9 40 10 19 Singlepass Micromist 1.3 35 5 20 PFA-LC 0.75 40 5 21 Burgener 0.5 45 5 22 Crossflow 0.9 45 10
23 Totalconsumption PFA-LC 0.51 Notcontrolled 50 9
24 PC3 PFA-LC 0.65 −5◦C 20 3 25 Micromist 0.4 25 5 26 Burgener 0.55 15 3 27 Opalmist 0.35 25 5 28 Savillex 0.4 25 5 29 SpectroSmall PFA-LC 0.85 Notcontrolled 45 8 30 Micromist 0.85 45 8 31 Burgener 0.5 50 8
MS/MSwithHMItubing.Theamountofoxygenwasoptimizedby monitoringcarbonemissionbandwhenintroducingorganic sol-vent,byvisuallyassessingthatnocarbonwasdepositedonthe samplercone.Then,thecarriergaswasoptimizedintherangeof 0.3to0.9L/minforeverysystem.TheintensityofLi,YandTlwas monitorwhilechangingcarriergasvalue.Suchoptimizationwas performedforeverycombinationofnebulizersandspray cham-bers(#1to#31)asshowninTable3.Anexampleofthecarriergas optimizationisshowninsupplementaryinformationFig.S1. 2.2. UHPLCinstrumentconditions
FlowinjectionanalysiswasperformedwithanACQUITYUPLC I-Class system (Waters, Milford, MA, USA), including a high-pressurebinarysolventpumpwithamaximumdeliveryflow-rate of2mL/min,anautosamplerwithaflow-throughneedleof15L, acolumnovenwithamaximumtemperatureof90◦Candadiode arraydetectorwitha500nLflow-cellwithstandingpressureupto 70bar.Theinjectionvolumewas1L.Thewavelengthwassetat 407nmforporphyrindetection.Dataacquisitionwithasampling rateof40HzandinstrumentcontrolwasperformedbyEmpower software. All experiments were performed withacetonitrile as mobilephaseat400L/min(exceptfortotalconsumptionspray chamberworkingat200L/min),usingazero-deadvolumeunion inplaceofthecolumn.Theoventemperaturewas30◦C.TheDAD detectorwasconnectedtothenebulizerwithaPEEKtubing.Its dimensionswereselecteddependingonthespraychamberdesign, namely67cmx65mforAgilent8800,SpectroLargeand Single-pass and 111cmx100m for Twinnabar, Impact bead, Spectro Small,PC3,IsoMist,andtotalconsumption.
2.3. Chemicalsandsamplepreparation
2,3,7,8,12,13,17,18-Octaethyl-21H,23H-porphine vana-dium(IV) and LC–MS grade acetonitrile (ACN) were purchased
from Sigma-Aldrich (Steinheim, Germany). Tetrahydrofuran (unstabilized) UHPLC/MS grade, obtainedfrom Biosolve Chimie SARL(Dieuze,France)wasusedassamplesolvent.SPEXCertiPrep (Metuchen, NJ, USA) Co, Ce, Y, Tl,Li monoelemental standards in2%HNO3 (1000g/L)wereusedtopreparethemultielement standard solutionused forcalibration. This solutionwith1ppb Co,Ce,Y,Tl,Liinacetonitrilewasusedfordailycalibrationofthe ICP-MS/MS.Porphyrinsamplewaspreparedataconcentrationof 10ppminTHF.Solutionswerestoredat5◦C.
3. Resultsanddiscussion
3.1. Comparisonof31commerciallyavailableinterfaces
Extra-columnsolutedispersionwasevaluatedinflowinjection analysisbyinjectingasampleofporphyrin,usingtwodifferent detectors (i.e.UV and ICP-MS/MS)in series and a SISinterface betweenthem.Azero-deadvolumeunionwasusedinplaceofthe column.PorphyrinwasfirstdetectedbyUV,andthenbyICP-MS/MS atm/z=67.Thiscompoundwasfoundtobeattractivebecauseof thepresenceofchromophoresforUVdetectionandofchelated metalfor ICP-MS/MS detection. Thevariance ofdispersion due totheSISinterface(2
SIS)wasestimatedbysubtractingthepeak variance,resultingfromthesolutetravelintotheUHPLC/UV instru-ment(2
ext,UHPLC/UV),fromthetotalpeakvariance,resultingfrom
thewholesolutetravel(2
ext,total): 2 SIS =2 ext,total−2 ext,UHPLC/UV (1) The calculations of 2
SIS were based onthe assumption that thecontributionofbothzero-deadvolumeunionandICP-MS/MS analyzertototalsolutedispersioncouldbeconsideredasnot sig-nificantandhencecouldbedisregarded.
Table4
MeanValue(2
SIS(L2))andRelativeStandardDeviation(RSD)ofthepeakvariance, inducedbySISalone,aregivenforfiveconsecutiveinjections,for31combinations ofnebulizersandspraychambers(SISarerankedfromthelessdispersivesystemto themostdispersiveone).
# Nebulizer SprayChamber Meanvalue2
SIS(L2) RSD*(%)
3 PFA-LC Twinnabar 6 10.0
23 PFA-LC Total 8 58.8
1 PFA-LC IsoMist 11 18.2
12 PFA-LC Impactbead 12 13.3
24 PFA-LC PC3 42 4.8
20 PFA-LC Singlepass 44 13.6
29 PFA-LC SpectroSmall 70 20.2
2 MicroMist Twinnabar 84 1.1
11 MicroMist Impactbead 93 7.5
25 MicroMist PC3 93 8.6
19 MicroMist Singlepass 108 11.1
6 Savillex Twinnabar 125 10.4
8 PFA-LC Agilent8800 127 18.9
16 PFA-LC SpectroLarge 143 23.1
28 Savillex PC3 155 3.9
30 MicroMist SpectroSmall 188 4.8
7 MicroMist Agilent8800 370 2.2
5 Opalmist Twinnabar 642 2.2
14 Opalmist Impactbead 694 2.0
13 Burgener Impactbead 726 7.4
15 MicroMist SpectroLarge 865 5.5
27 Opalmist PC3 992 3.4
10 Burgener Agilent8800 1446 17.4
4 Burgener Twinnabar 1582 11.6
17 Burgener SpectroLarge 1657 16.8
9 Crossflow Agilent8800 1674 7.2
22 Crossflow Singlepass 1724 1.9
26 Burgener PC3 2658 7.6
18 Crossflow SpectroLarge 2771 2.6 31 Burgener SpectroSmall 3769 9.7
21 Burgener Singlepass 8070 22.3
*RelativeStandardDeviation.
Duetoseverepeakdistortions,especiallyduetoSIS,peak vari-ancesinvolumeunit,2
v,werecalculatedbymeansofthesecond ordercentralmoment,usinganin-houseprogram.
2
SIS values resulting from solute dispersion in 31 different combinationsof nebulizersand spray chambers(31 settingsas numberedin Table3)weredeterminedaccordingtoEq.(1).To ensureagoodreliabilityoftheresults,thesolutewasinjectedfive consecutivetimes.
Amongthe31differentSISinterfacesthatwereassessedwith respectto extra-columnband broadening, PC3, Twinnabar, and IsoMistarethemostreportedspraychambersintheliterature[1]. Thepeakvariancesweredeterminedwithoutcolumnforfive repli-cates.Meanvariancevaluesinvolumeunitsandthecorresponding RelativeStandardDeviations(RSD)werecalculatedforeachofthe 31SISinterfacesaloneandfortheUHPLC/UVsystemalone.Values forSISalone(2
SIS accordingtoEq.(1))arelistedinTable4.The meanvariancevaluefortheUHPLC/UVsystem(2
ext,UHPLC/UV)was
about8L2.Thisvaluewasfoundtobequiterepeatable(RSD<5%), therebyhighlightingthereliabilityofthecalculationmethod.As
canbeseeninTable4,therangeof2
SISvalues,dependingonSIS, isverylarge(from6to8070L2).UnlikeUHPLC/UVsystem,the determinationof2
SISwaspoorlyrepeatableformostSISwithRSD valuessometimeshigherthan25%.ForSIS#23,theRSDvaluewas evencloseto60%whichmightarisefromthedesignofthespray chamberwhereintheaerosolisnotsortedoutbutentirelysent totheplasma,makingsolutedispersionuneven.Moregenerally, solutedispersioninSISappearstobelessrepeatablethanintherest oftheUHPLC-UV/ICP-MS/MSsystem,suggestingamoreuncertain dispersionprocessthanwithUVdetection.
Thelowestpeakvariance(i.e.6L2)wasfoundwithTwinnabar as spray chamber and PFA-LCas nebulizer (SIS#3in Table 4).
Fig.1.PeaksobtainedwithoutcolumnusingtheTwinnabarspraychamberand fivedifferentnebulizers:SIS#4Burgener;SIS#5Opalmist;SIS#6Savillex;SIS#2 MicroMist;SIS#3PFA-LC;UHPLC/UVSystem.Sample:porphyrin(10ppminTHF). Detectedelement:67V.Totalextra-columnpeakvariancesaregivenabovethepeak apex(inL2).1Linjected.Nocolumn.Mobilephase:ACN.407nm.400L/min.
Different SIScombiningTwinnabarand differentnebulizersare compared in Fig. 1.The studied nebulizersincludedconcentric (Opalmist,Savillex,MicroMist,andPFA-LC)andparallelpath (Bur-gener)ones.ThepeaksshowninFig.1werenormalizedinorderto betterhighlighttowhatextentthepeakbroadeningcandecrease the peak intensityand hence increase the signal-to-noiseratio (S/N). Itis clearthat thepeakshapes aresignificantly different dependingonthenebulizer.Somepeaksaresymmetricalbutlarge, someothersarethinnerbutwithseverepeaktailing.Verybadpeak shapesalwaysresultinlowsignal-to-noiseratios(S/N),well corre-latedwithhighpeakvariances.Theworstpeakshapewasobtained withtheBurgenernebulizerwhichledtoameasuredpeakvariance closeto1600L2.Suchasignificantdispersioncanarisefromthe largeinternaldiameter(i.e.380m)oftheconnectingcapillary locatedbetweenUV-detectionandthenebulizerbutalsofromthe nebulizeritselfduetoitslargeorificeanditslargeinternal vol-ume(108L).Thislatterhasbeendesignedtoavoid theriskof cloggingwhichmakesthisnebulizerveryattractivewhen parti-clesorsaltsarepresentinthesample.Burgenerisexpectedtobe ideallyoperatedathighflow-rates(i.e.>800L/min)ratherthan 400L/minasinthepresentstudy.Thismaycontributetofurther explaintheverylargepeakobservedinFig.1.BothOpalmistand SavillexnebulizersledtolowS/Nvaluesinadditiontosignificant bandbroadening(peakvarianceof653and136L2respectively) makingthemalsoinappropriateforUHPLCseparations.Thebest peakshapesandhencethebestS/Nvalueswereobtainedwith PFA-LCorMicroMistasnebulizers.ItcanbenoticedthatbothPFA-LCand MicroMistweredesignedwithlowinternalvolumes,(i.e.2and6L respectively),therebyexplainingthelowpeakvariances.However, thevariancevaluewithMicroMist(92L2)wassignificantlyhigher thanwithPFA-LC(6L2)whichisduetotheirdifferenceinvolume butalsototheirdifferentdesignwhichcanaffectsolute disper-sionashighlightedbytheseverepeaktailingincaseofMicroMist (Fig.1).AcomparisonofthepeaksobtainedwithMicroMist(Fig.2a) orPFA-LC(Fig.2b)anddifferentspraychamberisgiveninFig.2.A significantpeaktailingalongwithlowS/Ncanbeobservedwith all studiedspray chamberswhen using MicroMist asnebulizer