How are isotopes differentiated in mass spectrometry?

In mass spectrometry, isotopes are differentiated based on their distinct mass-to-charge ratios.

Mass spectrometry is a powerful analytical technique that is used to identify the amount and type of chemicals present in a sample by measuring the mass-to-charge ratio and abundance of gas-phase ions. This technique is particularly useful in differentiating isotopes, which are atoms of the same element that have different numbers of neutrons and hence different atomic masses.

The process begins with the ionisation of the sample, where it is bombarded with a stream of electrons to knock off one or more electrons, creating positive ions. These ions are then accelerated through an electric field, which gives them the same kinetic energy. Following this, the ions enter a magnetic field where they are deflected along a curved path. The extent of this deflection depends on the mass-to-charge ratio of the ions. Lighter ions and those with a higher charge are deflected more than heavier ions or those with a lower charge.

This is where the differentiation of isotopes comes into play. Isotopes of the same element will have the same charge after ionisation, as they have the same number of protons. However, they will have different masses due to the different number of neutrons. This means that they will be deflected by the magnetic field to different extents, allowing them to be separated and detected individually.

The ions then hit a detector, creating an electric current. The strength of this current is proportional to the abundance of the ions, allowing the relative abundance of different isotopes to be determined. The results are displayed as a mass spectrum, a graph of intensity (relative abundance) against mass-to-charge ratio. Each peak in the spectrum represents an isotope, with the position of the peak indicating the mass-to-charge ratio (and hence the mass) of the isotope, and the height of the peak indicating its relative abundance.

In summary, mass spectrometry differentiates isotopes based on their distinct mass-to-charge ratios, allowing the identification and quantification of different isotopes in a sample.