Exploring Chemical Analysis: Analytic techniques/week 6 reading Flashcards

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created 1 year ago by Thomaslymanmiller
updated 1 year ago by Thomaslymanmiller
science, life sciences, biophysics, chemistry, analytic
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What are the four basic components in all mass spectrometers?

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  • sample inlet
  • ionization source
  • mass analyzer
  • ion detector


What is electron ionization(EI) in mass spec?

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It requires a source of electrons in the form of a filament to which electric potential is applied, typically at 70 eV.


What is electrospray ionization?

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Passing the LC effluent through a capillary to which a voltage has been applied. The energy is transferred to the solvent droplets which become charged.

  • Ions observed in mass spectrometer were already present in solution on chromatography column; neutral analytes are not converted into ions by electrospray


What is an atmospheric pressure chemical ionization?

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Liquid from LC is introduced directly into the ionization source. However the droplets are not charged and the source contain a heated vaporizer to allow rapid desolvation of the drops.

  • New ions such as protonated analyte are created by chemical ionization


What is Matrix-Assisted Laser Desorption Ionization-Time of Flight(MALDI-TOF)?

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Ionization that is used for the analysis of biomolecules such as peptides and proteins.


What is a quadrupole?

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The analyzer consists of four rods or electrodes arranged across from each other. As the ions travel through the quadrupole they are filtered according to their m/z(mass to charge ratio) value so that only a single m/z value ion can strike the detector.


What is selected ion monitoring(SIM)?

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  • Specific masses can be selected to monitor a few target analytes
  • mass spectrometry scanning mode in which only a limited mass-to-charge ratio range is transmitted/detected by the instrument


What is an ion trap?

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  • trap and store ions in an orbital motion within the ion trap and eject ions for detection.
  • use oscillating electric fields (radio frequency [RF]) to trap ions in a controlled manner. A typical quadrupole ion-trap mass spectrometer consists of a ring electrode with a hyperbolic inner surface and two electrically common hyperbolic end-cap electrodes.


What is tandem mass spectrometry?

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  • a two-step technique used to analyze a sample either by using two or more mass spectrometers
  • used for greater selectivity and lower detection limits. A common form of MS/MS is to link three quadrupoles in series. Generally each quadrupole has a separate function.


What is collision induced (activated) dissociation?

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Ions are accelerated to high kinetic energy and allowed to collide with neutral gas molecules to fragment the ions


What is small molecule analysis used for?

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  • aids in the identification and quantification of the metabolites of drugs and drug candidates, and their interactions.


What is proteomics?

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is the large-scale study of proteomes. A proteome is a set of proteins produced in an organism, system, or biological context.


How does Matrix-Assisted Laser Desorption Ionization-Time of Flight (MALDI-TOF) detect pathogens?

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Isolated bacterial or fungal colonies can be directly spotted on the MALDI plate and ionized, which results in a "protein fingerprint" comprised mainly of ribosomal proteins.


What is the most common mass separator in use today?

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transmission quadrupole mass spectrometer


What is electron ionization?

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Molecules entering the ionization chamber are converted into ions


What is a molecular ion?

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Some (,0.01%) analyte molecules (M) absorb enough energy (9–15 electron volts, eV) to ionize. The resulting cation, M+.


What is a base peak?

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The most intense peak in a mass spectrum


How is chemical ionization different from electron ionization?

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it usually produces less fragmentation than electron ionization.

For chemical ionization, the ionization chamber contains a reagent gas such as methane at a pressure of ,1 mbar. Energetic electrons (100–200 eV) convert CH4 into a variety of products:


What is a reconstructed total ion chromatogram?

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One way to use a mass spectrometer as a detector for chromatography is to record the total current from all ions produced by eluate.


What are selected ion chromatograms?

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selected ion chromatograms in which the mass spectrometer is set to respond to just one mass in each trace.


What is Atomic mass?

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is the weighted average of the masses of the isotopes of an element


What is molecular mass?

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of a molecule or ion is the sum of atomic masses listed in the periodic table


What is nominal mass?

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a molecule or ion is the integer mass of the species with the most abundant isotope of each of the constituent atoms


What is the nitrogen rule?

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If the molecular mass of an unknown compound to the nearest integer value is an odd number, the compound contains an odd number of nitrogens in its molecular formula. Correspondingly, if the molecular mass is an even number, the compound contains zero or an even number of nitrogens in its molecular formula.


What are each sample injection best at?

• split: routine method

• splitless: best for quantitative analysis

• on-column: best for thermally unstable solutes


How does a flame ionization detector work?

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eluate is burned in a mixture of H2 and air. Carbon atoms (except carbonyl and carboxyl carbon atoms) produce CH radicals, which go on to produce CHO+ ions in the flame:


What is Hydrophilic interaction chromatography (HILIC) is used for?

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to separate molecules that are too polar to be retained by reversed-phase columns. In biochemistry, HILIC is useful for separating peptides and saccharides (sugars).