The Functioning of a Mass Spectrometry

When used in conjunction with other identification techniques, such as carbon and proton NMR and IR spectroscopy, mass spectrometry can be highly effective when attempting to determine the identity of an unidentified molecule.

FREMONT, CA: Mass spectrometry  (MS) is an analytical laboratory technique that separates sample components based on their mass and electrical charge. A mass spectrometer is an instrument used in MS. It generates a mass spectrum that displays the mass-to-charge ratio (m/z) of compounds in a mixture.

The primary components of a mass spectrometer are the ion source, mass analyzer, and detector.

Ionization: Initial samples may consist of solids, liquids, or gases. A sample is vaporized into a gas by losing an electron, then ionized by an ion source. Even ordinarily, anionic or nonionic substances are transformed into cations (e.g., halogens like chlorine and noble gases like argon). The ionization chamber is maintained in a vacuum so the generated ions can go through the device without colliding with air molecules. Ionization is caused by electrons produced by heating a metal coil until electrons are released. These electrons collide with the sample molecules, knocking one or more electrons loose. Since it requires more energy to remove multiple electrons, most cations created in the ionization chamber have a single electron charge. A positively charged metal plate propels the sample ions to the subsequent component of the machine.

Acceleration: The ions are subsequently accelerated by a potential difference and concentrated into a beam in the mass analyzer. The objective of acceleration is to provide every species with the same amount of kinetic energy.

Deflection: The ion beam traverses a magnetic field that deflects the charged stream. Lighter or more ionically charged components will deflect more in the field than heavier or less charged components.

There are numerous varieties of mass analyzers. If all particles have the same initial charge, their velocity is determined by their mass, with lighter particles reaching the detector sooner. The time-of-flight (TOF) analyzer accelerates ions to the same potential and measures how long it takes them to reach the detector. Other detectors monitor how long it takes a particle to reach the detector and how much it is deflected by an electric or magnetic field, providing additional information beyond mass.

Detection: A detector determines the number of ions at various deflections. The data is shown as a graph or a spectrum of multiple masses. Detectors then measure the induced charge or current created by an ion striking or passing a surface. The signal is amplified significantly to generate a spectrum. Due to the extremely low signal strength, an electron multiplier, Faraday cup, or ion-to-photon detector may be utilized.

Uses of MS

MS is utilized in qualitative and quantitative chemical analyses. It may identify the elements and isotopes in a sample, determine the masses of molecules, and identify chemical structures. It can also measure the purity and molar mass of samples.

Pros and Cons

MS has a significant advantage over many other techniques since it is susceptible (parts per million). It is an outstanding instrument for identifying unknown components in a sample or confirming their presence. MS has the disadvantages of not being able to identify hydrocarbons that create identical ions and being unable to distinguish between optical and geometric isomers. Combining MS with other methods, such as gas chromatography (GC-MS), compensates for its drawbacks.