Introduction to instrumental analysis仪器分析（美国密歇根州立大学） 英文版.pdf

CEM 333Instrumental AnalysisSimon J.GarrettRoom:CEM 234Phone:[phone] ext 208E-mail:garrettcem.msu.eduLectures:Tuesday,Thursday 9:00-9:50 am Room 136Office Hours:Tuesdays 10:00-11:00 amCEM 333 page 1.1Course ObjectivesTeach fundamentals of instrumental analysisLecture:Discuss theory and background for(1)chemical/physical property measured(2)origin of chemical/physical property(3)instrument design and nature of response(4)signal processing and relationship between readoutto property measuredLaboratory:Provides hands-on experience in(1)relating lecture material to practical analysis(2)design and operation of a real instrument(3)measurements on range of instruments(4)example analyses to illustrate value of techniqueCEM 333 page 1.2Introduction(Chapter 1)Classification of Analytical MethodsQualitative instrumental analysis is that measured propertyindicates presence of analyte in matrixQuantitative instrumental analysis is that magnitude of measuredproperty is proportional to concentration of analyte in matrixSpecies of interestAll constituentsincluding analyte.Matrix-analyte=concomitantsOften need pretreatment-chemical extraction,distillation,separation,precipitation(A)Classical:Qualitative-identification by color,indicators,boiling points,odorsQuantitative-mass or volume(e.g.gravimetric,volumetric)(B)Instrumental:Qualitative-chromatography,electrophoresis and identificationby measuring physical property(e.g.spectroscopy,electrodepotential)Quantitative-measuring property and determining relationshipto concentration(e.g.spectrophotometry,mass spectrometry)Often,same instrumental method used for qualitative andquantitative analysisCEM 333 page 1.3Types of Instrumental Methods:PropertyExample MethodRadiation emissionEmission spectroscopy-fluorescence,phosphorescence,luminescenceRadiation absorptionAbsorption spectroscopy-spectrophotometry,photometry,nuclearmagnetic resonance,electron spinresonanceRadiation scatteringTurbidity,RamanRadiation refractionRefractometry,interferometryRadiation diffractionX-ray,electronRadiation rotationPolarimetry,circular dichroismElectrical potentialPotentiometryElectrical chargeCoulometryElectrical currentVoltammetry-amperometry,polarographyElectrical resistanceConductometryMassGravimetryMass-to-charge ratioMass spectrometryRate of reactionStopped flow,flow injection analysisThermalThermal gravimetry,calorimetryRadioactivityActivation,isotope dilution(Often combined with chromatographic or electrophoretic methods)CEM 333 page 1.4StimulusResponseAnalyte(in matrix)EnergyAnalyticalDataencodedinformationExample:SpectrophotometryInstrument:spectrophotometerStimulus:monochromatic light energyAnalytical response:light absorptionTransducer:photocellData:electrical currentData processor:current meterReadout:meter scaleData Domains:way of encoding analytical response in electrical ornon-electrical signals.Interdomain conversions transform information from one domain toanother.Light IntensityPhotocell CurrentCurrent Meter ScaleDetector(general):device that indicates change in environmentTransducer(specific):device that converts non-electrical toelectrical dataSensor(specific):device that converts chemical to electrical dataCEM 333 page 1.5Non-Electrical DomainsElectrical DomainsPhysical(light intensity,color)CurrentChemical(pH)VoltageScale Position(length)ChargeNumber(objects)FrequencyPulse widthPhaseCountSerialParallelTime-vary with time(frequency,phase,pulse width)Analog-continuously variable magnitude(current,voltage,charge)Digital-discrete values(count,serial,parallel,number*)CEM 333 page 1.6Digital Binary DataAdvantages(1)easy to store(2)not susceptible to noise221st bit2nd bit3rd bit4th bitHiLoCountSerial2021202122ParallelHiLoHiLoHiLoHiLo3 separatesignals20=1,21=2,22=4.CEM 333 page 1.7Performance Characteristics:Figures of MeritHow to choose an analytical method?How good is measurement?How reproducible?-PrecisionHow close to true value?-Accuracy/BiasHow small a difference can be measured?-SensitivityWhat range of amounts?-Dynamic RangeHow much interference?-SelectivityCEM 333 page 1.8Precision-Indeterminate or random errorsAbsolute standard deviation:s=xi x()2i0i=NN1Variance:s2Relative standard deviation:RSD=sx Standard deviation of mean:sm=sNAccuracy-Determinate errors(operator,method,instrumental)Bias:bias=x xtrueSensitivityCalibration sensitivity:S=dSignaldcc+Signalblank=mc+Signalblank(larger slope of calibration curve m,more sensitive measurement)Detection LimitSignal must be bigger than random noise of blankMinimum signal:Signalmin=Av.Signalblank+ksblankFrom statistics k=3 or more(at 95%confidence level)CEM 333 page 1.9Dynamic RangeAt detection limit we can say confidently analyte is present butcannot perform reliable quantitationLevel of quantitation(LOQ):k=10Limit of linearity(LOL):when signal is no longer proportional toconcentrationDynamic range:LOLLOQ102to 106Selectivity:No analytical method is completely free from interference byconcomitants.Best method is more sensitive to analyte thaninterfering species(interferent).Matrix with species A&B:Signal=mAcA+mBcB+SignalblankSelectivity coefficient:kB,A=mBmAks vary between 0(no selectivity)and large number(veryselective).CEM 333 page 1.10Calibration methodsBasis of quantitative analysis is magnitude of measured property isproportional to concentration of analyteSignal xorSignal=mx+Signalblankx=Signal SignalblankmCalibration curves(working or analytical curves)InstrumentResponse(Signal)blankSignalDLLOQLOLDynamic RangexSlope mCEM 333 page 1.11Example(if time):Analyte Concentration(ppm*)Absorbance0.0(blank)0.050.90.152.00.243.10.334.10.42*ppm=1 g per LDefine Variance and Covariance:Sxx=(xi x)2N 1Sxy=(xix)(yi y)N 1x=2.02y=0.238Sxx=2.022+1.122+0.022+1.082+2.082()4=10.8284=2.707Sxy=2.020.188()+1.12 0.088()+0.02 0.002()+.4=0.95624=0.23905Slope:m=SxySx=0.239052.707=0.0883Intercept:b=y mx=0.238(0.08832.02)=0.0596Calibration expression isAbsorbance=0.0883Analyte(ppm)+0.0596CEM 333 page 1.12Introduction to Spectroscopy(Chapter 6)Electromagnetic radiation(wave)description:Electric Field StrengthTime t or Distance xAmplitude AVelocity vWavelength 0Period ptime for 1 to pass fixed pointFrequency#of passing per s =1p Wavenumber#of per cm =1 Velocity vDistance point on wave travels persecondIn a vacuum:v=vvacuum=c=2.99782x108m/sA set of waves with identical(a)freqency(b)phase are calledcoherent.CEM 333 page 2.1Frequency is always fixed but velocity can vary!Waves slow down in medium(gas,liquid,solid)so v100 MJ/mol(x-ray)to 100 kJ/mol(UV-vis)E(Vibrational)1 to 100 kJ/mol(IR)E(Rotational)10-100 J/mol(microwave)Continuum Spectra:Very broad band spectra in emission from solidsProduced by blackbody radiation-thermal excitation and relaxationof many vibrational(and rotational)levels.Blackbody Spectrum(Fig 6-18)CEM 333 page 2.6Absorption SpectraPlot of Absorbance vs.or called absorption spectrumJust as in emisson spectra an atom,ion or molecule can only absorbradiation if energy matches separation between two energy statesAtoms:No vibrational or rotational energy levels-sharp line spectra withfew featuresFor example:Na 3s3p 589.0,589.6 nm(yellow)Na 3s5p 285.0,285.1 nm(UV)Visible enough energy for valence(bonding)excitationsUV and x-ray enough energy for core(inner)excitationsMolecules:Electronic,vibrational and rotational energy levels-broad bandspectra with many featuresE=Eelectronic+Evibrational+ErotationalFor each electronic state-many vibrational statesFor each vibrational state-many rotational statesmany featuresAbsorption spectra affected by(1)number of atoms in molecule(2)solvent moleculesmore featuresblurred featuresCEM 333 page 2.7Effect of Chemical State(Fig 6-19):CEM 333 page 2.8Relaxation Processes:Lifetime of excited state is short(fsms)-relaxational processesreturn excited species to ground stateNonradiative relaxationmany small collisional relaxationstiny temperature rise of surrounding speciesRadiative relaxation(emission)fluorescence(10-5 s)Resonance fluorescenceproduces emission at same energy/frequency/wavelengthas absorptioncommon for atoms(no V or R levels)Non-resonance fluorescenceproduces emission at lower energy(lower frequency/longerwavelength)than absorption(Stokes shift)common in molecules-vibrational relaxation occursbefore fluorescencePhosphorescenceProduced by long-lived electronic state(up to hours)CEM 333 page 2.9IRVisUVAbsorptionNonradiativerelaxationFluorescenceResonanceNon-resonanceE2E1E0Excitation methods:(i)EM radiation(ii)spark/discharge/arc(iii)particle bombardment(electrons,ions.)(iv)chemiluminescence(exothermic chemical reactiongenerates excited products)CEM 333 page 2.10Optical Spectroscopy and Instrumentation(Chapter 7)(IR,visible and UV)I0Ipathlengthbconcentration cTransmittanceT=II0Percent Transmittance%T=II0100%AbsorbanceA=logT=logII0=logI0IExamples:T=1.00(100%T),A=0.00T=0.10(10%T),A=1.00T=0.001(0.1%T),A=3.00CEM 333 page 3.1Beers Law:Basis for absorbance spectrophotometryA candA bsoA bcA=abcproportionality constantabsorptivity -units ofL/gcmIf units of concentration are M(mol/L)then use molar absorptivity A=bcunits of L/molcmPhenomena used for optical measurements,(1)Absorption(2)Emission(3)Luminescence(Fluorescence,Phosphorescence,Chemiluminescence(4)ScatteringIn all cases,response is proportional to concentration of analyteCEM 333 page 3.2Many optical instruments share similar design(1)stable radiation source(2)transparent sample holder(3)wavelength selector(4)radiation detector(5)signal processor and readoutFig 6-22CEM 333 page 3.3Radiation Sources:(Fig.7-3)CEM 333 page 3.4Continuum sources produce broad range of s(often blackbody)Heated solid(Globar,nichrome wire)(1-40 m)Tungsten lamp(300-3000 nm)Quartz Tungsten Halogen(QTH)lamp(200-3000 nm)high temperature(3500 K)EvaporationW(s)W(g)W(g)+I2(g)WI2(g)RedepositionWI2(g)+W(s)W(s)+I2(g)D2 lamp or Hg/Xe arc-lamp-(160-400 nm)electronic excitationD2+Eelectrical D2*D(KE1)+D(KE2)+hKE1+KE2+h=EelectricalBDEbond dissociation energyCEM 333 page 3.5Line Sources produce few discrete wavelengthsD2 lamp or Hg/Xe arc-lamp(400 nm)Atomic emission hollow cathode lamp(a)electron bombardment of cathode(b)sputtering of cathodeatoms(c)emission from electronically excited cathode atoms Fig.9-11Electrodeless discharge lamps(EDL)(a)Ar ions created by RF energy(b)ions collide with gaseousmetal atoms which then(c)emit excite(Fig.9-12)CEM 333 page 3.6LaserLight Amplification by Stimulated Emission of Radiation(a)pumping of excited state(b)stimulated emission to produceemission(Fig.7-5)CEM 333 page 3.7Population Inversion and Amplification:Fig 7-6CEM 333 page 3.8Need population inversion for lasingCannot produce population inversion in 2-level system(stimulatedemission becomes increasingly dominant).Need 3-or 4-levels Fig 7-7Lasing medium can be solid(Nd:YAG,semiconductor diode laserAlGaAs),gas(noble gas Ar+,He/Ne,CO2,N2)or liquid(dye)(Fig.7-4)Advantages intensemonochromatic(line sources)pulsed(10-15-10-6 s)or continuous wave(cw)coherentsmall beam divergenceCEM 333 page 3.9Wavelength Selectors:(Fig.7-2)CEM 333 page 3.10Ideal Output:Fig.7-11Filters:Absorption filter-colored glass or dye between two glass platesCEM 333 page 3.11Two filters can produce narrower bandFig 7-15Interference(Fabry-Perot)filter-two thin sheets of metalsandwiched between glass plates,separated by transparent materialGlassMetalDielectricMetalGlassWhite LightNarrow CEM 333 page 3.12Interference for transmitted wave through 1st layer and reflectedfrom 2nd layerdMetal filmMetal filmConstructive interference whenn=2dsinwhen 90,sin 1n=2dwavelength in glass!air=glassTherefore transmitted through filter is=2dnCEM 333 page 3.13Monochromators:Entrance slit Collimating lens or mirror Dispersion element(prism or grating)Focusing lens or mirror Exit slitPrism:(many older instruments)122112750 nm)thermocouples-junction thermometerbolometers-resistance thermometerpyroelectric devices-piezoelectric effectIn many cases,dark current reduced by cooling transducer(250K to 1.5 K)-reduces thermal excitation of electrons.CEM 333 page 3.23UV-Vis(Absorption)Spectrometry(Chapters 13,14)Beers Law:A=bc=logT=logII0=logI0IAbsorbance is additiveAtotal=A1+A2.=1bc1+2bc2.in a 2 component mixtureA1=1,1bc1+2,1bc2A2=1,2bc1+2,2bc2Limitations of Beers Law(pp 303-311):(1)Chemical effects-analyte associates,dissociates orreacts to give molecule with different Fig 13-3CEM 333 page 4.1(2)Physical effects-stray light,polychromatic radiationor noiseA1=logT1=1bc=logI0I 1I1=I0 1101bcI2=I0 2102bcA=I0 1+I0 2I1+I2 =I0 1+I0 2I0 1101bc+I0 2102bc A=log I0 1+I0 2()log I0 1101bc+I0 2102bc()CEM 333 page 4.2 non-linear calibration curve(Fig 13-4,13-5)CEM 333 page 4.3Typical UV-Vis Spectrophotometers:(Fig 13-12)includes selection(a)single beam(SB)(b)double-beam(DB)-in-space(c)double-beam-in-timeCEM 333 page 4.4Multichannel SpectrophotometerNo monochromator,but disperses transmitted light and measures allwavelengths at once (Fig 13-13)No scanning-simple and fastMore expensiveLimited resolutionCEM 333 page 4.5Applications of UV-Vis Spectrometry:M+hexcitation M*relaxation M+h/heatHow probable?ranges 0 to 100,000 L/molcmforbiddenallowedelectronic transitionWhich electrons get excited?In UV-Vis,photon provides enough energy to move outer valence(bonding)electronsOrganic molecules=sA+sBBonding molecular orbital*=sA sBAntibonding*molecular orbital=pA+pBBonding molecular orbital*=pApBAntibonding*molecular orbital Fig 14-1CEM 333 page 4.6,(bonding)and n(non-bonding)electrons Fig 14-2Arrange in terms of energy:Fig 14-3*E large(150 nm)=10-10,000 L/molcmn*(halogens,N,O,S)E smaller(=150-250 nm)=200-2000 L/molcm*n*E small(=200-700 nm)=10-10,000 L/molcmIdeal for UV-Vis spectrometry of organic chromophoreCEM 333 page 4.7Red shift of max with increasing conjugationCH2=CHCH2CH2CH=CH2 max=185 nmCH2=CHCH=CH2 max=217 nmRed shift of max with#of ringsBenzene max=204 nmNaphthalene max=286 nmBlurred with solvent Fig 14-5CEM 333 page 4.8Inorganic IonsMost transition metal ions are colored(absorb in UV-vis)due todd electronic transitions(Fig 14-7)Remember:Solution absorbs red appears blue-green Solution absorbs blue-green appears redCEM 333 page 4.9Ligands cause different interactions with d electrons(Fig 14-8,14-9)-ligand field splittingCEM 333 page 4.10Ligand Field Strengths:max for complex(nm)Increasing Ligand Field Strength 6Cl-6H206NH33en6CN-Cr(III)736573462456380I-Br-Cl-F-OH-C2O42-H2OSCN-NH3enNO2-Energy(T1)(difference is energy required to flip electron spin)Example:Na ground state 1s2 2s2 2p6 3s1s=1/2,2S+1=2,ground state doublet s electronwritten 3(2S)Two spin states of equal energy(up/down)CEM 333 page 5.2Na 1st excited state 1s2 2s2 2p6 3p1D1 written 3(2P)BUT two spins states?J(total ang.mom)=L+S or L-Snow 1s2 2s2 2p6 3s1=3(2P1/2)and 3(2P3/2)Term Symbol2S+1LJNa 3p3s fluorescence two lines at 589.6 nm(2P3/2)and 589.0 nm(2P1/2)S1Emission S0S1Absorption S0()CEM 333 page 5.3What about Lifetimes?Absorption:S1S0 very fast 10-15-10-13 s Relaxation:Resonant emission S1S0 fast 10-9-10-5 s(fluorescence)c