Intro to MS & Mass Analyzers 1: Time-of-flight Mass SpectrometryBusiness ItemsSlide 3Mass Spectrumm/zSignal IntensityMS OscilloscopeSlide 8Slide 9“A Universal Technique”Slide 11Mass Analyzer Resolving PowerSlide 13Ion Motion in Electrostatic FieldsTypes of Mass AnalyzersTime-of-Flight Mass SpectrometrySlide 17TOFMSActual Picture More ComplexResolutionImproving ResolutionSlide 22ReflectronComparison of DE vs ReflectronAn Inherent DilemmaPerformance Trade-offs: On AxisOrthogonal ExtractionoTOFMSSlide 29BACKUP and OLD SLIDESSlide 31Slide 32Slide 33Calculate resolution and accuracy?Slide 35Slide 36Slide 37Intro to MS & Mass Analyzers 1: Time-of-flight Mass SpectrometryCU- Boulder CHEM-5181Mass Spectrometry & ChromatographyJose-Luis JimenezFall 2009Lecture Slides adapted from 2007 lecture by Dr. Joel Kimmel, CU-BoulderBusiness Items•Review calendar for labs•Small change to pre-lab–Instead of matrices of CHCA, SA, DHB and urea, you will be using CHCA, SA, DHB and "no matrix". •TOFMS HW assigned later today by email–Igor simulation of TOFMS•Start looking for articles to present–1st journal skim due on Thu next weekA mass spectrometer determines the mass-to-charge ratio (m/z) of gas-phase ions by subjecting them to known electric or magnetic fields and analyzing their resultant motion.Mass SpectrumSignal intensity vs mass-to-charge ratiom/zThe mass-to-charge ratio is often referred to as m/z and is typically considered to be unitless:m: the mass number = atomic mass/u (u = 1/NA g)z: the charge number = Q/e (e = 1.6022 × 10−19 C)The Thompson has been proposed as a unit for m/z, but is only sometimes used.Historically, most ions in MS had z = 1, which is likely the cause for the confusion in units. But, due to new ionization techniques, this is no longer true.Signal IntensityDepending on the type of mass spectrometer, ions may be detected by direct impact with a detector or by monitoring of an induced current image.Recorded signal can be measured in:•Counts per unit time (Digital)•Voltage per unit time (Analog)•Power (Frequency domain)To a first approximation, relative signal intensity reflects relative ion abundanceMS Oscilloscopehttp://www.vias.org/simulations/simusoft_msscope.htmlAn ion with m/z = m has charge equal:(a) 1 Coulombs(b) m Coulombs(c) 1.6022 × 10−19 Coulombs(d) e Coulombs(e) I don’t know•Early stages of MS: Precise determination of atomic masses and isotope abundances.•Last 50 years: Shift towards analytical applications involving molecules of greater complexity•Last 15 years: Explosion of biological applications•1897: J.J Thompson discovers electron and determines in m/z•1912: JJ Thompson constructs first mass spectrometer•1918: Demster develops electron ionization source•1942: First commercial instrument for organic analysis•1956: First GC-MS •1974: First HPLC-MS•1987: MALDI demonstrated; 1988 ESI Demonstrated; shared Nobel Prize in 2002See extended history in introduction of DeHoffmann“A Universal Technique”SampleIonization SourceMass AnalyzerDetector•Analysis by MS does not require: •Chemical modification of the analyte •Any unique or specific chemical properties•In theory, MS is capable of measuring any gas-phase molecule that carries a charge •Analyzed molecules range in size from H+ to mega-Dalton DNA and intact viruses•As a result, the technique has found widespread use•Organic, Elemental, Environmental, Forensic, Biological, Reaction dynamics …All experiments have this basic backbone, but range of applications implies a diversity of experimental approaches. PC (Acquisition and Analysis)SampleIonization SourceMass Analyzer“A mass spectrometer determines the mass-to-charge ratio (m/z) of gas-phase ions by subjecting them to known electric or magnetic fields and analyzing their resultant motion.”The ionization source imparts energy into the sample in order to drive (i) conversion to gas-phase (if necessary) and (ii) ionization of moleculeThe mass analyzer manipulates the motion of the ions. Requires vacuum! (Consider mean free path)Many systems will require transport of gas-phase sample from atmospheric pressure to vacuum, before or after ionizations step.Mass Analyzer Resolving PowerMass peak width ( Δm50%)Full width of mass spectral peak at half-maximum peak height Mass resolution / Resolving Power (m / Δm50%)Quantifies ability to isolated single mass spectral peakMass accuracyMass accuracy is the ability to measure or calibrate the instrument response against a known entity. Difference between measured and actual mass Figure from: M. P. Balogh, LC-GC Europe, 17(3), 152–159 (2004)Which of the following pairs requires the greatest mass resolving power to distinguish:(A)Ar+ from Ar2+(B) CO+ from N2+(C) CH3+ from CDH2+(D) I don’t know(E) I need a coffeeInfo:Ar = 39. 9623837 u, C = 12 u, O = 15.9949 u, N = 14.003 u, H = 1.007 u, and D = 2.0141 uIon Motion in Electrostatic Fields •Electrical force on an ion:EqFEQ: Would ions originating at X and Y be arrive at negative surface at the same time?A. YesB. X will arrive before YC. Y will arrive before XD. I don’t knowE. I still need a coffeeElectric Field Lines++++++-------XYTypes of Mass Analyzers•Time-of-flight (TOF)•Sector–Magnetic–Electric•Quadrupoles•Ion traps•Orbitrap•Ion-Cyclotron Resonance (ICR)–Fourier Transform (FTMS)•HybridsTime-of-Flight Mass SpectrometryBipolar TOF voltage schemeVm/z  t1/2Relative Intensitym/z  t1/2Relative Intensitym/z  t1/2Relative Intensitym/z  t1/2Relative Intensitym/z  t1/2Relative Intensitym/z  t1/2Relative IntensityDeborah GrossCarleton CollegeTime-of-Flight Mass SpectrometryTime-of-Flight Mass SpectrometryTo determine m/z valuesA packet of ions is accelerated by a known potential and the flight times of the ions are measured over a known distance.Q: What are V, e, and z? Key Performance NotesBased on dispersion in timeMeasures all m/z simultaneously, implying potentially high duty cycle“Unlimited” mass rangeDC electric fieldsSmall footprintRelatively inexpensiveTOFMSDetectorVSource, SDrift Region, DE = V/SE = 0mqEsDvDtmqEsvmvqEsqEsqVUaDDaDDaaa22212Ions accelerated by strong field, E, within short source region, S.Drift times recorded across long, field-free drift region, D.vD depends on starting position of ion – ideally all ions start from same plane.Q: What else is ideally assumed (Uo, E, D, …)?Q: What