Mass Spectrometry

• Mass spectrometry is a powerful analytical technique used to quantify known materials, identify unknown compounds within a sample, and elucidate the structure and chemical properties of different molecules.

• It works by ionising chemical compounds to generate charged molecules or molecule fragments and measuring their mass-to-charge ratios.

• The process consists of three basic steps: Ionisation, Acceleration and Detection.

• Ionisation: It is the process through which molecules are converted into ions. This is typically achieved by losing or gaining electrons to generate positively or negatively charged ions.

• Among the most common ionisation methods are Electron Impact (EI), where a molecule is bombarded with a beam of electrons, and Electrospray Ionisation (EI), which involves passing a high voltage through a solution or sample to create a fine mist of charged droplets.

• Acceleration: After ionisation, the ions are accelerated by an electric field. The resulting ions often have the same kinetic energy leading to a separation due to their different masses.

• Detection: Ions are then sorted based on their mass-to-charge ratio (m/z) and abundance. The lighter ions are deflected more than heavier ones. An ion with a charge of +1 will be deflected more than an ion with a charge of +2 of the same mass.

• When an ion hits the detector, it triggers a response that is amplified to generate an electrical signal. From this, a spectrum can be created.

• The mass spectrometry spectrum of a pure substance is a line spectrum and can be used to identify the substance or to determine its relative molecular mass. Each peak in the spectrum corresponds to an ion with a specific mass-to-charge ratio (m/z value) and the peak’s height represents the relative abundance of that ion.

• Tandem Mass Spectrometry (MS/MS) is an important technique where ions are separated based on their mass, selectively fragmented, and the product ions are then separated and detected.

• It is important to note that mass spectrometry is a destructive technique, meaning that it often breaks the sample down during the process.

• Mass spectrometry is used in various fields including pharmaceuticals, forensics and environmental analysis due to its ability to provide detailed information about molecular structures and to quantitatively measure very small amounts of substances.