Differences Between Base Peak and Molecular Ion

In a mass spectrometer, molecules are broken down into charged pieces known as ions, which are then sorted based on their masses. The vertical axis shows the highest content of ions. A mass spectrum is a chart that contains the masses of the pieces as well as a measurement of their relative abundance. The most intense point in a spectrum is referred to as the “Base Peak,” and its intensity is set to 100%. This ion is the most common in the ionisation chamber and the most stable, making it valuable for identifying the molecule.

It is typically feasible to identify the precise mass of the molecules being studied and to derive information about molecular structure from the masses and frequency of the lines in a mass spectrum. 

The relative intensity of each ion in a mass spectrum is generally determined by utilising the peak with the greatest intensity as the “standard” or “base” peak.

Molecular Ion

The release of one electron from an electrically neutral molecule results in the formation of a molecular ion. A molecular ion is a covalently bound set of two or more atoms or a metal complex that behaves as a single unit and has a net charge that is more than zero. Because the electron mass is so little in comparison to the mass of a molecule, the mass of a molecular ion is considered the same as the mass of the molecule.

Base Peak

Contrary to popular belief, base peaks may not always be molecular ions, and molecular ions are often not base peaks. The ion formed due to the loss of one electron is known as the molecular ion. A radical cation is something like a molecular ion. It is a cation due to its positive charge and a radical because not all of its electrons are located in pairs. Because one electron is so light in comparison to the weight of all the protons and neutrons in the molecules, the molecular ion has the same mass as the original molecule.

Molecular Ion Peak Vs Base Peak

The molecular ion peak is the peak in a mass spectrum that represents the molecular ion (symbol: M peak). The molecular ion peak is the point with the largest mass-to-charge ratio after excluding any peaks induced by the existence of heavier isotopes. The most powerful (tallest) peak in spectral data is caused by the ion with the highest abundance (relative intensity; peak height along the y-axis). 

Of course, the molecular ion has the same configuration as the parent molecule, except for one electron. So, where does the missing electron originate? Typically, the following pattern is observed:

• Electrons are most readily removed from non-bonded pairs because bonding electrons have lesser power and are more stable (which is the fundamental aim of creating a bond), making them harder to remove.
• If no non-bonded pairs exist, electrons are more readily removed from pi bonds because pi bonds have greater energy than sigma connections.

Differences Between Base Peak and Molecular Ion

The heaviest ion in the mass spectrum (the one with the highest m/z value) is most likely the molecular ion. Or The molecular ion peak is the peak in a mass spectrum that represents the molecular ion (symbol: M peak). The molecular ion peak is the peak with the largest mass-to-charge ratio after excluding any peaks caused by the presence of heavier isotopes.

The base peak in a mass spectrum is the most intense (tallest) peak attributable to the ion with the largest relative abundance (relative intensity; peak height along the y-axis). Contrary to popular belief, molecular ions are not always base peaks, and base peaks are not always molecular ions.

The only fragment ions are CO (m/z=28) and O (m/z=16), and the molecular ion is likewise the base peak. Propane’s molecular ion has m/z=44 as well; however, it is not the most prevalent ion in the spectrum. A carbon-carbon bond cleavage produces methyl and ethyl fragments, one of which is a carbocation and the other a radical.

Conclusion

The most intense peak in a spectrum is known as the “Base Peak,” and its intensity is set to 100%. This ion is the most common in the ion source and the most stable, making it valuable for identifying the molecule. An ion is generated by removing one or more electrons from (positive ions) or adding one or more electrons to (negative ions) a molecule without fragmentation of the molecular structure. The peak at m/z=72 is the molecular ion and hence indicates the molecule’s molecular mass.

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