(AOM) Mass Spectrometry Lesson

Mass Spectrometry

Mass Spectrometry, or MS, is when a compound is bombarded with a stream of electrons so that the compound breaks into fragments. Each compound gives a unique set of fragments which can be thought of as that compound's "fingerprint". It is a complex piece of equipment in the Forensic lab capable of identifying materials in which other methods, such the Photospectrometer, have been unsuccessful. Mass Spectrometry, as mentioned above, functions by bombarding samples with electrons, high heat or electrical force to break down molecules into ions. The ions are then separated and categorized by their mass. Next, the ions, grouped by mass, are detected by an electron multiplier. An electron multiplier functions, as one would expect, to multiply the charge of the electrons. This causes the sample to be "showered" with electron charge. This shower of electron charge produces a distinctive pattern of fragmentation that is essentially a "fingerprint" for that substance. Finally, these fragmentation patterns, or "fingerprints", are compared to reference samples of known substance fingerprints for positive identification. Mass Spectrometers usually are paired with Gas Chromatography equipment. This is because Gas Chromatography produces a very pure sample for the Mass Spectrometer to analyze. The Mass Spectrometer (image left) is able to more accurately identify unknown substances based on the "fingerprint" fragment patterns, whereas Gas Chromatography can only identify the substance based on the retention time. See the sample below.

Mass Spectrometry has multiple uses in the Forensic lab, such as:

Identification of unknown substances (Ex: White powder form of a drug at a crime scene)
Drug testing of athletes for performance-enhancing drugs and illegal substances
Analysis of accelerants in arson cases
Detection and identification of explosives in bombings

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