Mass Spectrometry and Atomic Mass Review

This set covers key vocabulary regarding Relative Atomic Mass, the principles and interpretation of Mass Spectrometry, and the definitions of Empirical and Molecular formulas.

Relative Atomic Mass ($A_r$)

The weighted average of all the different relative isotopic masses ($I_r$) of an element.

Mass Spectrometry

An analytical technique used to determine the relative masses of molecules by generating and detecting positively charged ions.

Destructive Technique

A method of analysis, such as mass spectrometry, that breaks molecules into fragments, meaning the sample cannot be recovered.

Molecular Ion ($M^+$)

Also referred to as the parent ion, it is the first ion formed when an electron is removed from a sample molecule by an electron beam.

Fragmentation

The process where a molecular ion breaks up into smaller positively charged ion fragments and uncharged free radicals.

Free Radical ($R\cdot$)

An uncharged species with an unpaired electron produced during fragmentation that is not detected in a mass spectrometer.

Mass/Charge Ratio ($m/z$)

The value plotted on the x-axis of a mass spectrum; since VCAA assumes ions with a $1+$ charge, it is equivalent to the mass of the fragment.

Isotopic Mass Spectroscopy

A technique used to determine the number of isotopes, their relative isotopic masses ($I_r$), and their percentage abundance.

Base Peak

The most abundant fragment ion produced in mass spectrometry, which is assigned a relative intensity of $100$.

Isotope Effect (M+1 peak)

A small peak with an $m/z$ of the molecular ion $+ 1$, occurring because a small portion of molecules contain isotopes such as $^{13}C$, $^2H$, or $^{17}O$.

Empirical Formula

The simplest whole-number ratio of atoms of different elements in a compound.

Molecular Formula

The actual number of atoms of different elements covalently bonded in a molecule.

Relative Isotopic Mass ($I_r$)

The mass of a specific isotope, indicated by the position of peaks on the x-axis in an isotopic mass spectrum.

Percentage Abundance

The relative amount of each isotope present in a sample, indicated by the height of the peaks in an isotopic mass spectrum.