3Lecture 1:Introduction to Mass Spectrometry & Sample Introduction TechniquesCU- Boulder CHEM 5181Mass Spectrometry & ChromatographyProf. Jose-Luis JimenezFall 20064Concept of Mass SpectrometrySample InletIon SourceMassAnalyzerDetector RecorderFrom Watson5Example MS• The mass spectrum shows the mass of the molecule and the masses of pieces from it– Much simpler than other types of spectra6History of Mass Spectrometry – Pre-MS• 1886: E. Goldstein discovers anode rays (positive gas ions) in gas discharge• 1897: J.J. Thomson discovers the electron and determines its m/z ratio. Nobel Prize in 1906.• 1898: W. Wien analyzes the anode rays by magnetic deflection, and establishes that they carry a positive charge. Nobel Prize in 1911.• 1909: R.A. Millikan & H. Fletcher determine the elementary unit of charge.7History of MS – Early Years • 1912: First Mass Spectrometer (J.J. Thomson)• 1919: Electron ionization and magnetic sector MS (A.J. Dempster)• 1942: First commercial instrument8History of Mass Spectrometry – Recent • 1953: Quadrupole and the ion trap (W. Paul and H.S. Steinwedel). Nobel Prize to Paul in 1989.• 1956: First GC-MS• 1968: First commercial quadrupole• 1975: First commercial GC-MS• 1990s: Explosive growth in biological MS, due to ESI & MALDI• 2002: Nobel Prize to Fenn & Tanaka for ESI & MALDI• 2005: Commercialization of Orbitrap MS• More info: “Measuring Mass: From Positive Rays to Proteins”, M. Grayson, Ed., 2002.• http://masspec.scripps.edu/information/history/pdf/nobel2002.pdf9Growth of Mass SpectrometryAttendance of the ASMS annual conference:10Why is Mass Spectrometry so Succesful? Because of its:A. High Sensitivity– ability to detect very small amounts)B. High Selectivity– Ability to tell molecules apart in a mixtureC. High Time ResolutionD. Low CostE. I honestly don’t know11Why is Mass Spectrometry so Succesful? II12Lectures on MSHigh VacuumSample InletIon SourceMassAnalyzerDetector RecorderMS1TodayMS2-3 MS4-5 MS5InterpretationI 1-613The Need for Vacuum I1. Why do we need vacuum in a MS instrument?A. Ions can only be made under vacuumB. Ions are lost if not under vacuumC. Ions can only be mass-analyzed under vacuumD. All of the aboveE. I don’t know2. How much vacuum is enough for MS?A. 10-3AtmB. 10-7AtmC. 10-10AtmD. It depends on the instrumentE. I don’t know14The Need for Vacuum II• λ = 0.66 / P–Where λ is in cm and P in pascals– Need λ = 10 to 100 times the ion path to reduce the probability of ion / neutral collision to 10%, or better 1%– Typical ion path: 0.2 m (quad) to 2 m (TOF)–P = 10-4mbar => l = 0.66 m–P = 10-5mbar => l = 6.6 m• Note that 1 mbar = 100 Pa; 1 Atm = 1012 mbar15The Need for VacuumMean Free Path of Gas Molecules vs. Pressure1E-081E-061E-041E-021E+001E+021E+041E+061E+081E-12 1E-10 1E-08 1E-06 1E-04 1E-02 1E+00 1E+02 1E+04Pressure (mbar)Mean Free Path (cm)16References on Vacuum Technology• We don’t have time to cover vacuum technology but two excellent references are:– J.H. Moore et al., “Building Scientific Apparatus,” Westview Press, 3rdEd., 2002. ($65)• Chapter on web page (password-protected)– J.F. O’Hanlon, “A Users’ Guide to Vacuum Technology,” Wiley Interscience, 3rdEd., 2003. ($95)17Sample Introduction Techniques• Objective: convert sample into gas-phase molecules– Without loss of vacuum• Ions freqently made under vacuum– But trend towards high pressure ion sources (ESI, DESI, DART…)Ion Source10-6mbarSolidLiquidGas103mbar18Question• How much gas / liquid sample (e.g. cm3/ min) does a MS need? – What limits the minimum? – What limits the maximum?19Allowable Flow Rate into MS: Gas•Gas sample– E.g. direct sampling of atmospheric air, or volatiles from pyrolized sample, or output of GC• Assume 1 cm3/ min at ambient pressure–107to 108cm3/ min at the MS pressure– Pumping speed: 167 to 1670 l/s – Typical range of pumping systems for MS: 50 to 1000 l/s20Allowable Flow into MS: Liquid• Liquid sample– E.g. direct analysis of chemical process fluid, or output of LC or CE• Assume H2O, 0.1 cm3/ min– Gas flow = 0.1 / 18 moles * 24,500 cm3/mol = 136 cm3 / min @ atmospheric pressure– Gas flow into MS = 22,700 to 227,000 l/s• Beyond the range of the pumping systems• Typically the eluent of LC or CE cannot be evaporated into the MS21Brainstorming on Sample Introduction• How could we possibly introduce a sample (gas / liquid / solid) into the high vacuum of a mass spectrometer?22Types of Sample Introduction Systems1. Batch inlets– Introduce all components of the sample at once2. Continuous inlets– Can be used to look at processes as f(t)• E.g. variability in the atmosphere• Also time-resolved output of a chromatograph23Batch 1: Heated Reservoir24Batch 1: Heated Reservoir - Notes• Used for Liquids or solids• Reservoir is evacuated• Valve to ion source is opened, to check for residues from previous samples• Valve to ion source is closed• Then sample is introduced with microsyringe into septum• Valve is open, sample lasts 15-30 min.– Can heat up to help evaporation– Can heat more to clean up before the next sample• Used for mass calibration compounds such as perfluorokerosene• Advantage: Constant signal for a while• Disadvantage: inefficient -> requires large sample25Batch 2: Direct Inlet Probe26Batch 2: Direct Inlet - Notes• Used for solids with low vapor pressure• Inlet tip introduced into vacuum through a vacuum lock• Often sample is heated– Sometime micropyrolisis oven, e.g. polymers, bacteria• Advantages: Small distance: efficient, can be used for low vapor pressure• Disadvantages: – Increases risk of venting– Increases risk of contamination (large amounts of sample)– Separation with thermal gradient27Batch 2.1: Heated Direct Inlet - Example• Thermogram allows some separation– Much less than in chromatography• Below: work of Paul Ziemann on secondary organic aerosols28Continuous 1 (g): Direct Injection29Direct Injection Notes• GC: typically 250 um diameter column, 25 m long, 1-2 cm3/ min of carrier gas• Be careful about what you put on MS!!– Particles from column– Outgassing30Continuous 2 (l): Particle Beam Interface31Particle Beam Notes• Liquid is atomized into droplets (few microns)• Heating to evaporate most of the solvent (down to 100 nm)• Differential focusing of the particles vs. the gas allows concentration of the particles• Differential