Gas Chromatography Mass Spectometry Introduction
| GCMS is especially useful for air samples
but can be used to detect, quantify, and identify chemicals
in air, water, soil, plant and animal tissue, and many other
substances. |
What do you use to measure trace amounts of chemicals in the air?
A very powerful and sensitive instrument used to study trace amounts
of chemicals in the air is a gas chromatograph
(CHROME-ah-TOG-rah) connected to a mass spectrometer
(spek-TRO-meh-ter), or GCMS. The GCMS can detect chemicals in amounts
as small as a picogram. That is 0.000000000001 gram. One picogram
is the equivalent of one drop of detergent in enough dishwater to
fill a trainload of railroad tank cars ten miles long. Many of the
pollutants found in air are present at concentrations lower than
one picogram in a cubic meter of air. It is important for an the
instrument to be able to detect these low concentrations.
But what exactly does the GCMS do?
 Separates
– The GCMS can separate the complex mixtures of chemicals
found in air or water. This works like runners in a race. Everyone
begins the race together at the starting line but faster runners
reach the finish line before slower runners. In this case, speed
is measured by volatility. More volatile chemicals move faster than
less volatile chemicals.
 Quantifies
– The GCMS tells you the amount of each chemical present in
a sample by comparing to a standard,  a
pre-measured known amount of the chemical also measured on the GCMS.
Identifies – If your sample contains an unknown chemical,
mass spectrometry helps you determine the unique chemical structure,
which acts as a "fingerprint", of the unknown chemical.
The chemical fingerprints can be compared to a library of known
chemical fingerprints. If your unknown chemical is not in the library,
the fingerprint will help you develop a good idea of the chemical
structure.
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