Ar Ar + e - INDUCTIVELY+COUPLED+ PLASMA+SPECTROMETRY+ What+is+Plasma?+ FuncDon+of+Plasma+

Transcription

1 INDUCTIVELY+COUPLED+ PLASMA+SPECTROMETRY+ Applied'Analy+cal'and'Inorganic'Chemistry'Program' Department'of'Chemistry,'Faculty'of'Science' Mahidol'University' What+is+Plasma?+ Ar Ar + e - Plasma is an ionized gas that is macroscopically neutral. Source: FuncDon+of+Plasma+ Courtesy from Agilent desolva+on' 'vaporiza+on' 'atomiza+on' 'ioniza+on'

2 ICPMOES+or+ICPMMS+ Source: Today s Chemist at Work Volume 8, No. 10, 42-44, by Robert Thomas ionization excitation M M * -hν excitation M + M +* -hν Component+of+ICP+Spectrometer+ ICP-OES ICP-MS Aerosol+generaDon+and+sample+transport+in+plasma+ spectrometry+! Key'components'! Nebulizer'! Spray'Chamber'! Plasma'! Key'basic'parameters'! Drop'size'distribu+on'! Mass'transport'of'aerosol'! Loss'processes'occuring'in' spray'chamber'! Solvent/plasma' interac+on' Nebulizers+ Pneumatic nebulizer Cross flow nebulizer Concentric nebulizer sample solution gas aperture V-groove V-groove nebulizer

3 Ultrasonic+Nebulizer+ A piezoelectric crystal vibrates at ultrasonic frequencies (50 khz to 4 MHz), and then causes sample solution to break up into small aerosols PneumaDc+VS+Ultrasonic+Nebulizers:+ aerosol+size+distribudons+ Source: Inductively Coupled Plasma Spectrometry and Its Applications, edited by Steve J. Hill, CRC Spray+Chamber+ " Result'! Removal'of'larger'droplets'G'd'>'10'µm' " Goal'! Avoid'overloading'of'ICP'! Guarantee'efficient'atomiza+on'&'ioniza+on' " Phenomena'occurring'! Removal'of'larger'droplets'by'impac+on'on'chamber'walls'! Solvent'evapora+on'! Coagula+on'of'smaller'droplets' " Analyte'introduc+on'efficiency'! Reduced'to'1G2%'with'tradi+onal'PN' ScoRMType+DoubleMPass+ Spray+Chamber+ cooling water in to ICP (1 2 %) water jacket cooling water out to waste

4 Cyclonic+Spray+Chamber+ Source: to ICP side view top view ICP+Torch+Assembly+ Velmer Fassel ( ) Source: icp.tecmec.co.uk/whatisicp.html Source: Plasma+GeneraDon+ Source: icp.tecmec.co.uk/whatisicp.html AUXILIARY GAS NEBULIZER GAS Plasma+IgniDon+

5 Why+Argon+Plasma?+ " High'ioniza+on'energy'(15.76'eV)' " Chemically'inert'(cheapest'noble'gas)'! Simple'spectrum'! Capable'to'excite'and'ionize'most'of'the'elements' of'the'periodic'table'! No'stable'compounds'are'formed'between'argon' and'the'analytes' Plasma+Fire+Ball+ Ar Ar + e - Source: Component+of+ICP+Spectrometer+ ICP-OES Axial+or+Radial+ Axial Radial Source:

6 Axial+Plasma+CharacterisDcs+ Optical light path Recombination zone (severe matrix effect) Emission zone (no matrix effect) Courtesy from Spectro Analytical Instruments Excitation zone (slight matrix effect) OPI+operaDng+principle+ Adjustable argon jet Optical light path to spectrometer Recombination matrix effects Plasma Courtesy from Spectro Analytical Instruments Air+shear+gas+to+displace+the+cool+plume+ Source: DetecDon+System+ Sequential instrument Simultaneous instrument Source:

7 Component+of+ICP+Spectrometer+ ICP-MS Sample+IonizaDon+in+the+Plasma+ IonizaDon+in+ICP+ analyte ionization electron impact: M + e - M + + 2e - Penning ionization: Ar* + M M + + Ar + e - IonizaDon+Efficiency+in+ICP+ Degree of ionization (α) Ionization energy IE (ev)

8 IonizaDon+Efficiency+of+Elements+ InducDvely+Coupled+Plasma+ Ion+Source+for+Mass+Spectrometry+ PlasmaMSpectrometer+Interface+ " Sampling'cone' " Skimmer'cone'! Allows'introduc+on'of'ions'into'the'vacuum'chamber'! Material:''Nickel,'Pla+num'

9 " As'the'ion'beam'passes'through'the'sampler'cone'into'the' skimmer'cone,'expansion'will'take'place,'but'its'composi+on' will'be'maintained.' Natural+tendency+for+the+ions+to+repel+each+other+ " With'the'rapid'drop' in'pressure'in'the' lens'chamber,' electrons'diffuse' out'of'the'ion'beam.'

10 " Therefore,'there'is'a'clear'need'to'electrosta+cally'steer'the' ions'of'interest'back'into'the'center'of'the'ion'beam'by'placing' voltages'on'one'or'more'ion'lens'components' Lens+System+

11 quadrupole filter rf DC source Basic+Principle+of+ Quadrupole+Mass+Filter+ high mass filter low mass filter + bandpass mass filter = Quadrupole+Mass+Analyzer+ Ion+DetecDon:++ ConDnuous+Dynode+Electron+MulDplier+ multiplication effect multiplication factor: pulse counting mode vs. analog mode

12 Ion+DetecDon:++ Discrete+Dynode+Electron+MulDplier+ Dynodes Pulse multiplication factor: pulse counting mode vs. analog mode + From Mass Analyzer SAMPLING+TECHNIQUES+IN+ INDUCTIVELY+COUPLED+PLASMA+ SPECTROMETRY+ Hydride+GeneraDon+ Gaseous'sample'introduc+on'! Produc+on'of'hydride'of'target' element' Source: Hydrides'separated'from'solu+on'in' gas/liquid'separator'! Hydrides'transported'into'ICP'by' means'of'ar'carrier'gas' Hydride+GeneraDon+ " Advantages'! 100%'analyte'introduc+on'efficiency'! Separa+on'of'analyte'elements'from'matrix' # Reduc+on'of'spectral'&'nonGspectral'interferences' " Disadvantages'! Limited'applica+on'range' # As,'Bi,'Ge,'Pb,'Sb,'Se,'Sn'and'Te'! Specific'sample'preGtreatment'required' # ph'has'to'be'adjusted' # Correct'oxida+on'state'of'target'elements'required'

13 " combining'normal' pneuma+c'ac+on,' within'a'special'spray' chamber,'to'transport' both'normal'elements' and'hydride'elements' simultaneously,' without'adversely' affec+ng'either'' Source: Concomitant Metal Analyzers (CMA) Sampling+Accessories:+Laser+AblaDon+ Source: (ICP-MS Beginner s Guide) Electrothermal+Vaporizer+ CMA+Nebulizer+ by+jobinmyvon+horiba,+france+ ETV-ICP-MS Source: (ICP-MS Beginner s Guide)

14 ICPMOES+Measurement:+Procedure+ Development+ Line'selec+on' Tuning' Matrix'effects' Method'valida+on' Source: By Paul Gaines, Ph.D. Edited by Brian Brolin Precision Sensitivity Line+SelecDon+ Spectral Interferences Line+SelecDon:+SensiDvity+ " Make'sure'that'the'line'is'not'too'sensi+ve'(i.e.'G' going'outside'the'linear'working'range).'dilu+ons' are'easy'' " Have'more'than'one'line'that'meets'your'lower'limit' of'detec+on'and'quan+ta+ve'measurement' requirements' Line+SelecDon:+Precision+ " Try'to'keep'the'analyte'concentra+on'well'within'the'linear'working'range' " Avoid'lines'requiring'spectral'correc+on' " Avoid'lines'that'are'in'spectrally'complex'regions' " Increase'the'integra+on'+me'' " Use'an'all'glass'introduc+on'system'including'a'glass'concentric'nebulizer' " Be'aware'of'high'salt'containing'solu+ons' " If'your'samples'and'standards'have'the'same'background'then'skip'background'correc+on' " If'the'matrices'of'the'samples'and'standards'can'be'matched'then'eliminate'the'peristal+c' pump'and'go''free'flow''' " Allow'the'instrument'to'warm'up'for'at'least'an'hour'and'work'in'a'controlled'temperature' environment'' " Clean'your'introduc+on'system'and'replace'the'tubing'when'necessary'

15 Line+SelecDon:+ Spectral+Interferences+ " direct'spectral'overlap' " wing'overlap' " near'neighbors' Spectrum+of+a+high+concentraDon+of+Fe+(red+line)+showing+a+direct+ spectral+overlap+upon+the+b line+and+a+wing+overlap+on+a+b Spectrum+of+a+high+Ca+containing+matrix+(red+line)+causing+a+sloping+ background+for+the+cu or+ge lines+ Background+correc-on+is+difficult!+ A+wing+overlap+interference+of+Fe+(red+line)+upon+the++ Ba nm+line+

16 Background+Enhancement+from+ Ca(II) and nm+Broadening++ A+nearby+Fe+line+interferes+with+the+background+correcDon+upon+the+Al nm+line.+ Nega-ve+values+of+background+corrected+intensity!+ Plasma+Diagnosis:+OpDmizaDon+ IonicMtoMAtomic+Line+Intensity+RaDo++ " Mg(II,' 'nm)/Mg(I,' 'nm)'! closeness'of'the'excita+on'energies'of'the'atomic' and'ionic'lines'! independent'of'the'detector'condi+ons'! wavelength'response'correc+on'is'not'necessary'! ra+o'above'8'indicates'robust'condi+on'

17 Effect+of+Plasma+Power+ Effect+of+Carrier+Gas+Flow+Rate+ Matrix+Effects+ " Slight'differences'in'the'matrix'can'cause'a'considerable' systema+c'error'having'a'definite'bias' Standard Addition Internal Standardization Solving Matrix Effect Problems Matrix Removal Internal+StandardizaDon:+ SelecDon+Criteria+ " Is'the'internal'standard'(IS)'element'compa+ble'with'your' matrix?''' " Are'there'any'possible'spectral'interferences'upon'the'IS'line?' " Is'the'concentra+on'of'the'IS'sufficient'to'give'a'good'signal'to' noise'ra+o?' " Can'your'sample'possibly'contain'the'IS'element'as'a'natural' component?' " Is'the'IS'clean?'' " Is'your'method'of'addi+on'of'the'IS'very'precise?'' " Do'you'always'use'the'same'lot'of'IS'for'the'standards'and' samples?' " If'your'plasma'temperature'were'to'go'up'or'down,'is'the'IS' likely'to'follow'the'same'paiern'of'intensity'change'as'the' analyte?'

18 Technique+of+Standard+AddiDons+ tedious but more reliable approach fastest approach for unknown matrices " At'least'two'spectral'lines'should'be'used'and'the' spectral'region'carefully'scanned'and'studied' " Aiempt'to'make'the'addi+ons'approximately'2x'and' 3x,'where'x'is'the'analyte'concentra+on'' ICPMMS+Measurement:+Procedure+ Development+ Tuning' Interferences' Matrix'Effects' Source: By Paul Gaines, Ph.D. Edited by Brian Brolin Why+OpDmize+(Tune)?+ " Op+mize'sensi+vity'! Maximize'signal'! Minimize'noise' " Verify'correct'mass'calibra+on' " Verify'correct'ion'ra+o'response' " Minimize'interferences'! Oxides'! Doubly'charged'ions'! Argides' Ion+Signal,+Plasma+Power,+ Nebulizer+Flow+Rate,+Sampling+Distance+

19 Ion+Signal,+Plasma+Power,+ Nebulizer+Flow+Rate,+Sampling+Distance+ Interferences+in+ICPMMS+ Isobaric Interferences Polyatomic Interferences Doubly Charged Ion Interferences Isobaric+Interferences+ Mass Element (% abundance) Interfering Isotope (% abundance) 46 Ti (7.95) Ca (0.0032) 48 Ti (73.45) Ca (0.179) 54 Fe (5.9) Cr (2.38) 58 Ni (67.76) Fe (0.33) 64 Zn (48.89) Ni (1.16) 114 Cd (28.81) Sn (0.65) 138 Ba (71.66) Ce (0.25) 152 Sm (26.63) Gd (0.2) Correction is possible. I (114Cd) = I (114) - (0.65/24.01)*I (118Sn) Polyatomic+(Molecular)+Interferences+ Source Interfering species Analyte isotope Support gas 40 Ar 80 2 Se Reagent acids 35 Cl 16 O 40 Ar 35 Cl 51 V 75 As Water, solvent 40 Ar 16 O 56 Fe Matrix elements 40 Ar 35 Cl 44 Ca 16 O 75 As 60 Ni

20 Even+high+purity+ water+can+lead+to+ spectral+ interferences!+ Spectral Interferences Due to The Presence of Cl Spectral Interferences Due to The Presence of C Spectral Interferences Due to The Presence of S

21 Spectral Interferences Due to The Presence of P Doubly+Charged+Ion+Interference+ Mass Interfering species Analyte isotope Ba 2+ Ga Nd 2+, 150 Sm 2+ As Pb 2+ Rh+ Matrix+Effects+ " Shil'of'ioniza+on'equilibria'in'plasma' " Ambipolar'diffusion'in'plasma' " Space'charge'repulsion'in'ion'op+cal'system,' ion'beam'dispersion,'space'charge'induced' scaiering' Shih+in+IonizaDon+Equilibrium+ in+presence+of+eies+ Ionization equilibrium in ICP M M + + e Ionization constant K M ni. n = n Ionization efficiency i a ni α = n + n a e KM = K + n M e constant constant With addition of easily ionizable elements (EIEs), n e increases with subsequently leading to decrease of ionization efficiency suppression most pronounced for high IP analyte elements

22 Ambipolar+Diffusion+Effect+ ICP M + ions electrons diffusion of electrons & M + ions mobility of electrons >> mobility of M + further diffusion of electrons causes M + ions to diffuse leading to lower M + density in center Space+Charge+Effects+ During+Ion+ExtracDon+ interface beam becomes enriched in postively charged particles extraction lens Matrix+Effects:+on+Lithium+ Signal B Zn Cd Au high ev Na Rb Cs U low ev Mass of matrix element Space charge effect Ionization effect Solvent+Effect In+ signal intensity (arbitrary units) 0.14 mol/l HNO % EtOH nebulizer gas flow rate (l/min) At lower plasma temperature, ionization requires longer residence time in ICP At higher temperature, ionization after shorter residence time in ICP

23 Intensity 1% HNO 3 5% HNO 3 20% HNO 3 Concentration of analyte QuanDtaDve+Analysis+Measurement+ Techniques+ External'Calibra+on' Standard'Addi+on' Isotope'Dilu+on' External+CalibraDon+ Intensity (cps) Concentration (ppb) External+CalibraDon+with+the+Use+of+ Internal+Standard+ " Avoid'M 2+ 'interferences' " Avoid'MO'and'other'molecular'interferences' " Any'naturally'occurring'internal'standard'element'in'the' sample'must'be'insignificant'in'comparison'to'the'amount' added' " Use'internal'standard'elements'as'close'as'possible'to'the' masses'of'the'analyte'elements' " Make'sure'the'matrix'doesn't'react'with'the'internal'standard' to'alter'(lower)'it's'concentra+on' " Common'internal'standard'elements'are'Li,'Be,'Sc,'Ga,'Ge,'Y,' Rh,'In,'Cs,'Pr,'Tb,'Ho,'Re,'Bi,'and'Th'

24 Method+of+Standard+AddiDon+ Intensity (cps) Concentration (ppb) Isotope+DiluDon+Technique+ Intensity Sample m/z Known quantities: - Sample amount - Isotope ratio Isotope diluted sample Intensity m/z Measure quantity: Isotope ratio of the isotope diluted sample Intensity Isotope spike m/z Known quantities: - Spike amount - Isotope ratio - Spike concentration " Concentra+on'of'Hg'in'sample'is'calculated'from'the' rela+ve'abundance'of' 201 Hg'and' 202 Hg'in'both'the'sample' and'spike' [Hg] = (A sp - RB sp ) x W sp (RB s A s ) x W s! '[Hg] '=''''concentra+on'in'ppm'! 'R' '=''''the' 201 Hg'to' 202 Hg'ra+o'! 'A sp '=''''the'spike' 201 Hg'abundance''! 'B sp '=''''the'spike' 202 Hg'abundance'! 'W sp '=''''the'spike'weight'in'µg'! 'A s '=''''the'natural' 201 Hg'abundance'! 'B s '=''''the'natural' 202 Hg'abundance'! 'W s '=''''the'sample'weight'in'g' Isotope+DiluDon+Technique+ " Advantages'! Excellent'correc+on'for'matrix'effects'! Aler'isotopic'equilibra+on:'analyte'losses'do'not'affect'result' # WellGsuited'in'case'of'matrix/trace'separa+on'! Isotope'ra+os'barely'affected'by'changes'in'sensi+vity'! Most'reliable'calibra+on'method' ' " Disadvantages'! Not'suited'for'monoGisotopic'elements' # Be,'Na,'Al,'P,'K,'Sc,'Mn,'Co,'As,'Y,'Nb,'Rh,'I,'Cs,'Pr,'Ho,'Tm,'Au,'Bi,'Th' # Some+mes':'use'of'longGlived'radionuclide'(e.g.,' 129 I)'! High'purchase'price'of'spikes' # '500G1000'US'$'/'100'mg' # Isotopic'enrichment'&'nuclide'(natural'isotopic'abundance)'! Analyte'concentra+on'has'to'be'approximately'known'! Less'suited'for'mul+Gelement'analysis'

25 Analyte+element:++InformaDon+on+the+web+ Source: Analyte+element:++InformaDon+on+the+web+ Source: Drawbacks+of+ICP+Emission+Spectrometry+ Typical+ICPMMS+Full+Mass+Spectrum+

26 ComparaDve+Spectral+Complexity:+ ICPMMS+vs.+ICPMOES+ Element Emission Lines Isotopes (natural) Alkali metals Lithium 30 2 Cesium Alkali earths Magnesium Calcium Transition metals Chromium Iron Cerium Volume 8, No. 10, 42-44, Robert Thomas AAS,+AES,+or+AMS+ SelecDon+Process+! Define'the'requirement''! Establish'criteria''! Define'the'task'in'detail''! Compare'techniques''

27 Comparison+of+AnalyDcal+Techniques+ Detection Limits Analytical Working Range Sample Throughput Purchasing Costs Interferences Skill Levels and Methodology DetecDon+Limit+Ranges+ AnalyDcal+Working+Ranges+ Sample+Throughput+ Flame AAS 3-10 s per element per sample GFAAS 2-3 min per element per sample ICP-OES elements in a few minutes ICP-MS elements in a few minutes

28 Interferences+in+Atomic+Spectroscopy+ Technique Type of Interference Method of Compensation Flame AAS GFAAS ICP-OES ICP-MS Ionization Chemical Physical Physical and chemical Molecular absorption Spectral Spectral Matrix Spectral Matrix Ionization buffers Releasing agent or nitrous oxide-acetylene flame Dilution, matrix matching, or method of additions Standard Temperature Platform Furnace (STPF) conditions, standard additions Zeeman or continuum source background correction Zeeman background correction Background correction or the use of alternate analytical lines Internal standardization Interelement correction, use of alternate masses, higher resolution systems or reaction/collision cell technology Internal standardization Skill+Levels+and+Methodology+ Three'criteria:' # Ease'of'use' # Operator'skill'level'' # Availability'of'applica+on'method' ApplicaDon+Examples+ " Copper'in'an'Electropla+ng'Bath'' " Lead'and'Cadmium'in'Blood'' " 22'Elements'in'Wastewater'' " 18'Elements'in'HighG'Purity'Hydrogen'Peroxide'' Summary:+ Choosing+AnalyDcal+Technique+ " No'one'technique'suitable'for'all'spectroscopic' applica+ons' " Each'has'strengths'and'weaknesses'that'must'be' evaluated'to'make'the'right'choice' " As'an'analy+cal'chemist,'you'are'commiied'to'supplying' data'of'the'highest'quality' " Your'success'could'depend'on'selec+ng'the'right'trace' element'technique'to'achieve'this'goal'