chapter 29

• Atomic and molecular masses are usually expressed in terms of _______ scale, based on a specific isotope of carbon.

  atomic mass scale
• this scale is equal to 1/12 the mass of a neutral 126C atom.

  One unified atomic mass unit
• the unified atomic mass is given the symbol?

  u
• One unified mass unit is commonly termed one

  Dalton (Da)
• The older term, atomic mass unit (amu), is to be discouraged since it was based on the

  most abundant stable isotope of oxygen 16O
• element in nature is given by summing the exact masses of each isotope weighted by its fractional abundance in nature

  The chemical atomic mass or the average atomic mass
• The ____________ is the type of mass of interest to chemists for most purposes.

  chemical atomic mass
• The atomic or molecular mass expressed without units is the

  mass number
• The _______, of an ion is the quantity of most interest because the mass spectrometer separates ions according to this ratio.

  mass-to-charge ratio (m/z)
• The _____ is an instrument that produces ions, separates them according to their m/z values, detects them, and plots the mass spectrum.

  mass spectrometer
• The purpose of the inlet system is to

  introduce a micro amount of sample into the ion source where the components of the sample are converted into gaseous ions by bombardment with electrons, photons, ions, or molecules.
• In atomic mass spectrometry, the ionization source is

  outside the evacuated region and also serves as the inlet.
• Deflection of ions in a magnetic field. Ion trajectories depend on m/z value.


  Magnetic sector
• focusing followed by magnetic field deflection. Trajectories depend on m/z values.

  Double-focusing Electrostatic
• Ion motion in dc and radio-frequency fields. Only certain m/z values are passed

  Quadrupole
• Storage of ions in space defined by ring and end cap electrodes. Electric field sequentially ejects ions of increasing

  m/z values.

  Ion trap
• Trapping of ions in cubic cell under influence of trapping voltage and magnetic field. Orbital frequency related

  inversely to m/z value

  Ion cyclotron resonance
• Equal kinetic energy ions enter drift tube. Drift velocity and thus arrival time at detector depend on mass.

  Time-of-flight
• Mass spectrometers require an elaborate vacuum system to maintain a low pressure in all of the components except the 


  signal processor and display.
• The most common transducer in the mass spectrometry is the

  electron multiplier
• These multipliers are trumpet-shaped devices made of glass heavily doped with lead.

  Continuous-dynode electron multipliers
• High-temperature argon plasma and Quadrupole

  Inductively coupled plasma, Direct current plasma, and Microwave-induced plasma
• The interface usually consists of two metal cones, called the

  sampler and the skimmer
• Analyte ions are then drawn into the mass spectrometer by

  differential pumping.
• was first used for routine chemical analysis in the early

  1940s when the petroleum industry adopted the technique for quantitative analysis of hydrocarbon mixtures produced in catalytic crackers.

  Molecular mass spectrometry
• the sample is first vaporized and then ionized.

  gas-phase source
• the sample in a solid or liquid state is converted directly

  into gaseous ions.

  desorption source
• The most widely used source is the ______. In this source, molecules are bombarded with a high-energy beam of electrons.

  electron impact (EI) source
• The purpose of the______ is to introduce a representative sample to the ion source with minimal loss of vacuum. 


  inlet system
• The conventional (and simplest) inlet system is the _____ in which the sample is volatilized externally and then allowed to leak into the evacuated ionization region.

  batch type
• technique that allows the mass spectrum of a preselected or fragmented ion to be obtained

  Tandem mass spectrometry, also called mass spectrometry-mass spectrometry (MS/MS)
• are obtained by scanning mass analyzer 2 while mass analyzer 1 is held

  constant to act as a mass selector for the precursor ion.

  Product-ion spectra
• can be obtained by scanning mass analyzer 1 and selecting a given product ion with

  mass analyzer 2.

  precursor-ion spectrum
• If both mass analyzers are scanned with a small offset in mass be-

  tween them,

  a neutral loss spectrum
• can be acquired by recording a product ion spectrum for each selected precursor ion, that

  is, by scanning mass analyzer 2 for various settings of mass analyzer 1.

  three-dimensional MS/MS spectrum
• When two or more analytical techniques or instruments

  are combined to form a new, more efficient device, the resulting methodology is often termed a

  hyphenated method
• has become one of the most powerful tools available for the analysis of complex organic and biochemical mixtures.

  Gas chromatography/mass spectrometry