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: www.midwestrefineries.com/refiningandassaying.htm FuncDon+of+Plasma+ Courtesy from Agilent desolva+on' 'vaporiza+on' 'atomiza+on' 'ioniza+on'
ICPMOES+or+ICPMMS+ Source: Today s Chemist at Work Volume 8, No. 10, 42-44, 47-48. 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
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 1999. 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
Cyclonic+Spray+Chamber+ Source: http://www.geicp.com/site/images/products/8090224he.jpg to ICP side view top view ICP+Torch+Assembly+ Velmer Fassel (1919-1998) Source: icp.tecmec.co.uk/whatisicp.html Source: http://hiq.linde-gas.fr/international/web/lg/fr/likelgspgfr.nsf/docbyalias/anal_icp Plasma+GeneraDon+ Source: icp.tecmec.co.uk/whatisicp.html AUXILIARY GAS NEBULIZER GAS Plasma+IgniDon+
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: www.midwestrefineries.com/refiningandassaying.htm Component+of+ICP+Spectrometer+ ICP-OES Axial+or+Radial+ Axial Radial Source: http://las.perkinelmer.com/content/technicalinfo/tch_dualviewicp.pdf
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: http://las.perkinelmer.com/content/technicalinfo/tch_dualviewicp.pdf DetecDon+System+ Sequential instrument Simultaneous instrument Source: www.siint.com/en/technology/icp_analysis1_e.html
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)
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'
" 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.'
" 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+
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: 107-108 pulse counting mode vs. analog mode
Ion+DetecDon:++ Discrete+Dynode+Electron+MulDplier+ Dynodes Pulse multiplication factor: 10 7-10 8 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: http://www.cetac.com/prods/hydride/hgx200.jpg! 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'
" 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: http://icp-oes.net/nebulisers.html Concomitant Metal Analyzers (CMA) Sampling+Accessories:+Laser+AblaDon+ Source: http://www.spectroscopymag.com/ (ICP-MS Beginner s Guide) Electrothermal+Vaporizer+ CMA+Nebulizer+ by+jobinmyvon+horiba,+france+ ETV-ICP-MS Source: http://www.spectroscopymag.com/ (ICP-MS Beginner s Guide)
ICPMOES+Measurement:+Procedure+ Development+ Line'selec+on' Tuning' Matrix'effects' Method'valida+on' Source: http://www.ivstandards.com/tech/reliability/part15.asp 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'
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+208.892+line+and+a+wing+overlap+on+a+b+ 208.959+ Spectrum+of+a+high+Ca+containing+matrix+(red+line)+causing+a+sloping+ background+for+the+cu+219.959+or+ge+219.871+lines+ Background+correc-on+is+difficult!+ A+wing+overlap+interference+of+Fe+(red+line)+upon+the++ Ba+233.527+nm+line+
Background+Enhancement+from+ Ca(II)+393.4+and+396.8+nm+Broadening++ A+nearby+Fe+line+interferes+with+the+background+correcDon+upon+the+Al+ 396.152+nm+line.+ Nega-ve+values+of+background+corrected+intensity!+ Plasma+Diagnosis:+OpDmizaDon+ IonicMtoMAtomic+Line+Intensity+RaDo++ " Mg(II,'280.270'nm)/Mg(I,'285.213'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'
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?'
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: http://www.ivstandards.com/tech/reliability/part16.asp 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+
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
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
Spectral Interferences Due to The Presence of P Doubly+Charged+Ion+Interference+ Mass Interfering species Analyte isotope 69 138 Ba 2+ Ga+ 75 150 Nd 2+, 150 Sm 2+ As+ 103 206 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
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+ 16 115In+ signal intensity (arbitrary units) 0.14 mol/l HNO3 14 12 10 8 6 4 2 2.5% EtOH 0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 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
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) 600000 500000 400000 300000 200000 100000 0 0 10 20 30 40 50 60 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'
Method+of+Standard+AddiDon+ Intensity (cps) 700000 600000 500000 400000 300000 200000 100000 0-10 -5 0 5 10 15 20 25 Concentration (ppb) Isotope+DiluDon+Technique+ Intensity Sample 201 202 m/z Known quantities: - Sample amount - Isotope ratio Isotope diluted sample Intensity 201 202 m/z Measure quantity: Isotope ratio of the isotope diluted sample Intensity Isotope spike 201 202 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'
Analyte+element:++InformaDon+on+the+web+ Source: http://www.inorganicventures.com/extras/pertable/ Analyte+element:++InformaDon+on+the+web+ Source: http://www.inorganicventures.com/extras/pertable/ Drawbacks+of+ICP+Emission+Spectrometry+ Typical+ICPMMS+Full+Mass+Spectrum+
ComparaDve+Spectral+Complexity:+ ICPMMS+vs.+ICPMOES+ Element Emission Lines Isotopes (natural) Alkali metals Lithium 30 2 Cesium 645 1 Alkali earths Magnesium 173 3 Calcium 662 6 Transition metals Chromium 2277 4 Iron 4757 4 Cerium 5755 4 Volume 8, No. 10, 42-44, 47-48. Robert Thomas AAS,+AES,+or+AMS+ SelecDon+Process+! Define'the'requirement''! Establish'criteria''! Define'the'task'in'detail''! Compare'techniques''
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 10-40 elements in a few minutes ICP-MS 10-40 elements in a few minutes
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'