Chemistry, as a discipline, seeks a complete molecular understanding of physical phenomena. Putting names and quantities to a phenomenon improves our understanding. A sub- discipline of chemistry, known as Analytical Chemistry, measures the integrity of a substance (the identity and amount).
Identifying a molecule or a chemical substance begins by approaching the unknown substance with a guarded respect. Understanding its chemistry gives us a foot in the door–an approach to identify molecular composition and function.
One of the properties chemists examine is the material’s boiling point and melting point.
Boiling Point and Melting Point
A molecule has a boiling point (liquid water, for example, characteristically boils at 212 degrees Fahrenheit or 100 degrees Celsius) and a melting point (frozen water has a melting point at 32 degrees Fahrenheit or 0 degrees Celsius). These two pieces of the puzzle assure a partial identification. The addition of calcium, magnesium, or other substances may alter the boiling and melting points of water, however, so the basic picture painted by boiling or melting a substance misses certain key points. More than a handful of physical properties characterize a molecule or substance; quantum mechanics can identify a substance’s actual chemical fingerprint.
Quantum Mechanics in Reactivity Measurements
Up until the mid-20th century, reactivity analysis methods utilizing physical properties identified chemical substances (molecules). However, the advent of Quantum Mechanics allowed chemists to utilize the chemical fingerprints of each substance for molecular identification. The ‘chemical fingerprints’ –much like their human counterparts, unambiguously identify molecules. For instance, the technique of Atomic Absorption Spectroscopy delineates the presence of calcium or magnesium in a water sample.
A fundamental notion of Atomic Absorption Spectroscopy says calcium, magnesium and elements like aluminum (dissolved in water) possess fundamental ‘fingerprints’ based upon Quantum Mechanics. Each of the atoms, subjected to a flame, will emit a characteristic color–or a measurable wavelength of light. Atomic Absorption Spectroscopy detects Arsenic or Chromium, as well.
Chemistry and Detection of TNT via Mass Spectrometry
Chemical components of explosives such as TNT normally contain carbon molecules (organic molecules) and a disproportionate amount of Oxygens or Nitrogens. Trinitrotoluene releases copious amounts of gas and energy during an explosion. In chemical shorthand, the equation follows:
4 C7H5N3O6 + 21O2 –> 28 C02 + 6 N2 + 10 H2 O + heat
TNT + oxygen –> carbon dioxide + nitrogen + water + energy
In essence, four molecules of TNT combine with 21 molecules of oxygen to release 28 molecules of carbon dioxide, and six molecules of nitrogen (plus gases and heat). –Or, four molecules suddenly produce vast amounts of heated gas and fire. But how can a chemical process identify TNT before it explodes?
When working to identify any substance, an unambiguous characterization starts with discerning its physical state. Is it a liquid or a solid? Is it volatile? Are there discernible vapors (is there an odor)? A material such as TNT possesses a discernible vapor, which is why properly-trained dogs can ‘sniff’ it out. The vapor also allows speedy, unambiguous characterization through Mass Spectrometry.
The technique of Mass Spectrometry, invented in the 20th century, identifies molecules by their atomic constituents. The process of Mass Spectrometry relies upon the knowledge that a molecule will fragment in a predetermined way–based upon the probabilities of quantum mechanics (as visualized by the Periodic Table). Passing an identical, known molecule through a Mass Spectrometer twice results in the same pattern each time (given identical parameters, or initial conditions).
While Mass Spectrometry is the go-to-technique– it presents a ‘mobility problem’ when needed in air ports and on-the-spot analyses at crash sites or remote locales. A technique that may be applied in the intermediate future is ‘TED’ or Trace Explosive Analysis.
Trace Explosive Detection (TED), a newer technique, utilizes laser light to molecularly ‘excite’ explosive residues. The technique is rapid and sensitive. The technique utilizes trace amounts through the technique of Raman Spectroscopy. Raman Spectroscopy measures minute changes in molecular orientation–the molecule vibrates, rotates and becomes increasingly energetic according to the probabilities of Quantum Mechanics (similar to the probabilities applied to Mass Spectrometry). Every molecule possesses a characteristic pattern or spectrum. The newer methodology utilizes mobile and intense (coherent) laser light– a few steps beyond the original Raman implementation. (Original Raman spectral analysis utilized light of single wavelength and not energetic, laser light.)
21st Century Methods of Chemical Analysis
While technology has utilized large, complex equipment to analyze any substance’s molecular structure, changes are on the horizon. Advances in miniaturization of chemical technology will allow scientists to use the methods in a laboratory on a smaller and simpler scale. The digitization of laboratory techniques allows faster turn-around and potentially ‘better speed to market’ as well.
The laboratory of the future will utilize on-spot-analysis in much the same way that laborers utilize tools or a plumber uses a tool chest. This trend, similar to Moore’s law of computer hardware, will take technicians out of the laboratory and directly to the field.