What is Mass Spectrometry?

Although not quite the know-it-all portrayed in televised fiction, mass spectrometry is a powerful, extremely useful tool for uncovering information about substances at the molecular level.

Introducing mass spectrometry

Mass spectrometry is one of the most advanced means of conducting research on individual molecules. By ionizing a sample of molecules, operation conducted in vacuum due to the high reactivity of charged particles, a mass spectrometer allows the differentiation and identification of individual components according to mass and charge. This is achieved by applying electric and magnetic fields to the ionized samples.

Because ions can be negative or positive, particles will be repelled or attracted to the mass spectrometer’s detector plate based on the polarity and strength of their electric charge. Further, passing through the magnetic field will bend the path of the ions into diverging arcs. This is the defining step in the overall differentiation, as any molecule’s response to a constant force field will be proportional with its own size.

A computer connected to the detector plate transforms the impulse signal of each impact into a data point. Once the sample has been run through, the complete readout will yield a spectrum depicting the relative abundance of ions within the total makeup of the sample. Each ion is identified by its specific mass-to-charge ratio (generally equal to that ion’s molecular mass) while the most abundant ion will by default be given a maximum peak in the readout.

The reason MS analysis provides a [i]spectrum[/i] output is the inevitable formation of fragment ions, where portions of the sample break into smaller ionic constituents. Carbon dioxide, for instance, would show partial fragmentation readings consistent with the molecular weight of CO and O ions.

The Mass Spec versatility

Present-day mass spectrometry is capable of distinguishing ions set apart by one unit atomic mass. In addition, the process has been refined for several highly-specialized applications: GC-MS can identify the different substances in unknown samples; MALDI makes it possible to analyze ionization-sensitive substances like organic polymers and biomolecules; TOFMS allows fine-particle analysis like dioxin screening; Tandem MS enables fragmentation analysis, making possible newborn screening.

Picture: Kasia Biel

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