Mass Spectrometry Techniques: High/Low Pass Filters, MALDI, ESI, Photoionization, and More, Quizzes of Geology

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TERM 1 High Pass Mass Filter DEFINITION 1 The X-Z plane electrodes only filter low mass ionsAdd a positive dc potential (at a fraction of the magnitude of the ac potential) to the rods in the X-Z plane TERM 2 Low Pass Mass Filter DEFINITION 2 Only low mass ions get to the detectorA negative dc voltage plus an ac potential which is the same magnitude but the opposite sign as the potential is applied to the X-Z plane TERM 3 Factors that influence particle striking during - RFcycle DEFINITION 3 Magnitude of the potential (amplitude) amount of time ions are accelerated towards rod (frequency of ac potential) mass of ion charge of ion position of ion in quadrupole TERM 4 Ambient Ionization Method DEFINITION 4 Allows the rapid analysis of samples or objects in their native state in the open environment with no prior prep TERM 5 DESI mechanism DEFINITION 5 wet the surface to dissolve analyte splash on the arrival of subsequent droplets with emission of secondary microdroplets sample is deposited on insulating surface surface is sprayed at high voltage nebulizing gas is flowed TERM 6 DART mechanism DEFINITION 6 electric potential causes electric discharge to produce a plasma containing electronic/vibronic excited state species gas flows into second chamber where electrode is biased to remove ions from gas stream third region is gas heating chamber. gas exiting through the third perforated electrode is directed toward the sample in front of the mass spec TERM 7 When are molecular ions observed in DART DEFINITION 7 When N2 is used TERM 8 What does N2 ionize? DEFINITION 8 Analytes that possess ionization potentials lower than the energy of the vibronic excited state.Unergoes penning ionization to get molecular ions TERM 9 Penning ionization DEFINITION 9 a form of chemi-ionization, an ionization process involving reactions between neutral atoms or molecules.Interaction between gas phase excited state atom or molecule, G*, and a target molecule M, resulting in the formation of a radical molecular cation M+, and electron, and a neutral gas moleculePenningionizationreferstotheinteractionbetweenagasphaseexcitedstateatomormoleculeG*andatargetmoleculeM,resultingintheformationofaradical TERM 10 What ions are produced with He? DEFINITION 10 [M +H]+ ionsprimarily produces 2^3S electronic excited statethis excited state rapidly reacts with atmospheric water and forms water clusters that protonate the analytes TERM 21 FAB/liquid-SIMS DEFINITION 21 fast atom bombardmentUse projectile to desorb/ionization molecules from a surfacesample is deposited in a viscous matrix (glycerol) TERM 22 Mechanism of FAB DEFINITION 22 Shock wave desorbs molcules Matrix assists pre-formation of ions in solution Localized high pressure gas right above surface promotes ion-molecule collisions and reactions (almost like a plasma) TERM 23 When is glycerol and nitrobenzyl used as matrix? DEFINITION 23 Glycerol- polar analytesNirobenzyl-nonpolar analytes TERM 24 FAB Polar Matrix DEFINITION 24 Has low vapor pressure, solubilizes peptides and other mid- sized biomoleculesassists in protonating analyte and replenishes the sample surface upon bombardment and absorbs excess energy to prevent sample degradation and fragmentationglycerol most commonly used TERM 25 Matrix Requirements for FAB DEFINITION 25 sample must be soluble in matrix only low-vapor pressure solvents can be used the viscosity must be low enough to ensure the diffusion of the solutes to the surface ions from matrix must be unobtrusive chemically inert ; specific ion formation reactions used to promote the secondary ion yield may occur TERM 26 Fab vs. Liquid SIMS DEFINITION 26 FAB- neutral beam, urually Ar or Xe, and orginial modeLiquid SIMS- ion beam, usually Cs+, beter replacementBoth require viscous matrix and generate similar types of ions TERM 27 Ion Production by FAB DEFINITION 27 Low polarity- M+medium polarity- M+, [M+H]+high polarity- [M+H]+, [M+Cat]+ionic K+A- - K+ [Kn+AN-1]+ TERM 28 EI DEFINITION 28 Generation of ions by intersecting gas-phase molecules with high energy electrons (70eV standard)requires volatile analyteionization energy dictates extent of fragmentationwidely used with GCharsh technique TERM 29 vertical ionization energy DEFINITION 29 maximum transition possibility TERM 30 adiabatic ionization energy DEFINITION 30 transition to lowest vibrational level of ion TERM 31 Photoelectron spectroscopy DEFINITION 31 technique used for determining the ionization potentials of molecules TERM 32 CI DEFINITION 32 widely used with GC requires volatile analyte gas-phase ion molecule reactions proton-transfer most common ability to control ion energetics better than EI TERM 33 Forming Negative Ions DEFINITION 33 Electron ionization: rarely used for neg. ions CI Resonant electron capture negative ionizationtypically uses EI of methane gas to produce thermal electrons TERM 34 Photoionization DEFINITION 34 photoabsorption causes ejection of an electron from the analytedegree of fragmentation depends on photon energycreates M+ radical cationstunable, but rarely more effective than EI TERM 35 Duty Cycle DEFINITION 35 portion of ions that are used to record part of the spectrum TERM 46 DIOS desorption/ionization on silica DEFINITION 46 matrix-free method that uses pulsed laser desorption/ionization on silica.structured silicon surfaces such as porous silicon or silicon nanowires are UV-absorbing semiconductors with a large surface area TERM 47 SELDI concept DEFINITION 47 load crude samples, wash, MALDI-MS TERM 48 supersonic expansion DEFINITION 48 achieved when a high pressure gas is expanded through a small orifice into a vacuum TERM 49 ESI DEFINITION 49 formation of highly charged liquid droplets from which ions are desolvated/desorbed very soft ionization low tolerance of non-volatile salts, detergents, buffer additives high sensitivity continuous ion source TERM 50 Taylor cone region DEFINITION 50 where electrostatic force balances surface tension of liquid TERM 51 What does high electric field do in ESI DEFINITION 51 keeps droplets from freezing by causing charged droplets to encounter many collisions (collisional warming)creates a double layer at the tip of the capillary TERM 52 When is ESI solvent oxidized? DEFINITION 52 in positive ion modeelectrolysis of water generates high concentration of protons TERM 53 When is ESI solvent reduced? DEFINITION 53 in negative ion modehigh local concentration of hydroxide ions TERM 54 Where does ESI oxidation reaction occur? DEFINITION 54 In the capillary causing electron flow to the voltage supply TERM 55 Where does reduction reaction occur in ESI? DEFINITION 55 capillary causing electron flow to capillary TERM 56 What does current measured at counter electrode do? DEFINITION 56 It balances the current at the capillary TERM 57 Evolution of an electrospray droplet DEFINITION 57 decreasing droplet size due to solvent evaporation increases repulsive forces between excess charges in the droplet (Coulombic explosion) droplets rupture when charge level reaches 80% of Rayleigh limit TERM 58 Rayleigh limit DEFINITION 58 point at which repulsive forces overcome cohesive forces of solvent TERM 59 What is the onset voltage of ESI a function of? DEFINITION 59 The capillary diameter and surface tension TERM 60 Ion desolvation is controlled by what in ESI? DEFINITION 60 temperature and flow rate of desolvation gas capillary-skimmer potential difference pressure in capillary-skimmer interface region