Mass Spectrometry, a Factual, Basic Primer

Mass Spec, a Fundamental Essential Tool for Ion and Molecular Study

Nov 15, 2009

Mass Spec and Cation Magnetic Fields , JPL NASA

Mass spectrometry is a factual, basic primer for ionic studies. The Nobel-Prize-winning "mass spec" can identify atoms and molecules with great specificity and accuracy.

Dr. Francis Aston of Cambridge, England developed the mass spectrometer in 1919 — in 1922, he received the Nobel Prize. Mass spectrometers enable atomic and molecular mass calculations with a precision of one part in 10,000. Mass spectrometry contributed to the discovery of many isotopes.

Mass Spectrometry, a Factual Basic Primer for Ions and Molecules

Mass spectrometers (photos 1, 2, 5, below) operate according to defined, physical-chemical laws outlined here:

sample atoms or molecules are injected into an ionization chamber under high vacuum.
an electron gun shoots a strong, electron beam at the samples in the spectrometer's ionization chamber. Samples include: gasses like helium, oxygen, nitrogen, or metals like mercury, lead, etc.
atoms or molecules experience electron loss, caused by the electronic beam.
atoms or molecules assume positive charges because of electron loss.
these positively-charged ions (cations) are gaseous.
newly-formed ions are propelled from the ionization chamber by an electric field generated by two metal grids.
Coulomb's law operates — the positive grid repels the positive ions, and the negative grid attracts these cations.
forces of attraction and repulsion are directionally similar for all the cations, and accelerate cations toward the cathode.
the cathodal grid has holes, and speeding cations pass through the holes at velocities inversely related to their masses — light ions travel faster than heavy ions.
each positively-charged ion produces an ionic, mini-magnetic field.
ions pass across an external magnetic field — the cationic and external fields interact.
each cation's trajectory bends in a curve related to its velocity and charge; velocity is inversely related to mass (photo 1) and an ion's charge influences bending in the curve, i.e. greater charge = more bending. (Note: m/z = mass/charge ratio of the atom or molecule).
uniform, or mixtures of, ion beams are analyzed as different masses impact a recorder plate (photographic or computer), and these ion particles converge at different points which relate to their different semicircular, radial paths. Magnetic fields can be adjusted to capture all relevant ions or molecules.
Modern mass spectrometers interact directly with computers which analyze and graph the physical data.

Mass Spec, Fundamental Essential Tool for Ion and Molecular Study

Mass spectrometry is invaluable for drug and pharmaceutical studies, proteomics, genetic analyses, genetic engineering, atomic and molecular analyses. A few, relevant, unique examples are illustrated.

Hair Analyses for Drugs and Heavy Metals. Each human hair grows about 1/2 inch a month over many months or years. Usually, fallen hair is replaced by new hair. Hair roots synthesize new hair protein (keratin). A rich blood supply nourishes the hair root where new keratin protein is synthesized and deposited . Various organic molecules (e.g drugs) and inorganic components (e.g. mercury, lead, arsenic), present in the blood, may incorporate with new keratin when present. Therefore, hair can be a nutritional record of a person's previous months, or years, of nutrition — hair ends are the oldest hairs, and the bases of hairs are the newest keratin. Lawrence Livermore Laboratory uses a laser to burn and punch holes into and along a hair with a thin, imaging-laser ablation technique. Laser ablation releases gaseous components that are whisked away to a mass spec for analyses (photo 3). Heavy metals and drugs, dirt, glass, paint chips and fibers from carpets and clothing can be analyzed.
Similar instrumentation under development will detect chemicals in air, and will permit monitoring of exhausts, smoke, and hazardous waste spills. LLNL scientists also have developed solid-phase microextraction (SPME) collection kits. Optical fibers serve as “chemical dipsticks” for safe, efficient sampling (photo 4). Commercial, hair-size (100-micrometer-thick) fibers within a polymer-coated syringe absorb thousands of chemical molecules for analyses. The polymer coatings can be customized for: chemical warfare agents, explosives, or illegal drugs. The collection fibers can be inserted directly into a portable (photo 5) or stationary GC–MS for immediate analysis.

Mass Spectrometry, Factual Primer Conclusions and Summary

Modern mass spectrometers are many, diverse and specialized, but all mass specs operate according to the features reviewed above. Mass spec techniques are, and will continue to, important in science.

Sources and Resources

Jet Propulsion Laboratory, NASA. The Mathematics of Mass Spectrometry.

Lawrence Livermore National Laboratory. Forsenics Science Center Maximizes the Tiniest Clue. Science and Technology Review, April 2002.

The copyright of the article Mass Spectrometry, a Factual, Basic Primer in Scientific Research Methods is owned by Donald Reinhardt. Permission to republish Mass Spectrometry, a Factual, Basic Primer in print or online must be granted by the author in writing.