Mass spectrum

Common fragmentation processes for organic molecules are the McLafferty rearrangement and alpha cleavage.

Straight chain alkanes and alkyl groups produce a typical series of peaks: 29 (CH3CH2+), 43 (CH3CH2CH2+), 57 (CH3CH2CH2CH2+), 71 (CH3CH2CH2CH2CH2+) etc.

The m/z is used in applied mass spectrometry because convenient and intuitive numerical relationships naturally arise when interpreting spectra.

However, mass information may be extracted when considering the whole spectrum, such as the spacing of isotopes or the observation of multiple charge states of the same molecule.

[7] By doing this he showed that the electron, which was postulated before in order to explain electricity, was in fact a particle with a mass and a charge and that its mass-to-charge ratio was much smaller than the one for the hydrogen ion H+.

In which he stated that all atoms (including isotopes) follow a whole-number rule[10] This implied that the masses of atoms were not on a scale but could be expressed as integers (in fact multiple charged ions were rare, so for the most part the ratio was whole as well).

In most forms of mass spectrometry, the intensity of ion current measured by the spectrometer does not accurately represent relative abundance, but correlates loosely with it.

For example, in electrospray sources in positive ion mode a quaternary amine will ionize exceptionally well whereas a large hydrophobic alcohol will most likely not be seen no matter how concentrated.

In other detection systems, such as FTICR, the number of charges on the ion are more important to signal intensity.

In order to make conclusions about relative intensity a great deal of knowledge and care is required.

A common way to get more quantitative information out of a mass spectrum is to create a standard curve to compare the sample to.

This requires knowing what is to be quantitated ahead of time, having a standard available and designing the experiment specifically for this purpose.

This situation occurs routinely as chromatographic components elute into a continuous ion source.

[11] Spectral skewing is not observed in ion trap (quadrupole (this has been seen also in QMS) or magnetic) or time-of-flight (TOF) mass analyzers because potentially all ions formed in operational cycle (a snapshot in time) of the instrument are available for detection.