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 (crow-MAT-oh-graf) 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. 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.



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.

In the Lab