M:e ratio

m:e ratio refers to the mass-to-charge ratio (m/e) which is a significant concept in Physics and Chemistry. It is a measurement used to identify and differentiate particles, especially ions produced in a Mass spectrometer. The m:e ratio is calculated by dividing the mass number (m) of an ion by its charge number (e).

History

The m:e ratio was first determined by J.J. Thomson in 1897 during his experiments on Cathode rays. Thomson's measurements of the m:e ratio of cathode rays led to the discovery of the electron. He found that the m:e ratio of the particles in cathode rays was over a thousand times lower than that of a hydrogen ion (H+), suggesting that these particles were either very light or highly charged.

Calculation

The m:e ratio is calculated by dividing the mass of an ion (in atomic mass units) by its charge (in elementary charge units). For example, a singly charged ion with a mass of 28 atomic mass units (such as a nitrogen molecule, N2+) would have an m:e ratio of 28.

Applications

The m:e ratio is used in mass spectrometry to identify and differentiate particles. By measuring the m:e ratio of ions, scientists can determine the mass and charge of the ions, and thus identify the molecules from which they originated. This is particularly useful in fields such as Biochemistry, where mass spectrometry is used to identify and quantify proteins and other large molecules.

See also

• Mass spectrometry
• J.J. Thomson
• Cathode rays
• Electron