Question

While 13C is the main contributor to the (M+1)+• peak, there are many other elements that can also contribute to the (M+1)+• peak. For example, there are two naturally occurring isotopes of nitrogen. The most abundant isotope, 14N, represents 99.63% of all nitrogen atoms on Earth. The other isotope, 15N, represents 0.37% of all nitrogen atoms. In a compound with molecular formula C8H11N3, if the molecular ion peak has a relative abundance of 24.5%, then what percent abundance do you expect for the (M+1)+• peak?

Answer 1

The percent abundance expected for the (M+1)+• peak is 0.37%.

Step-by-step explanation:

In mass spectrometry, the molecular ion peak (M) represents the species with the most abundant isotopes of each element in the compound. In the case of C₈H₁₁N₃, nitrogen has two naturally occurring isotopes: ¹⁴N and ¹⁵N, constituting 99.63% and 0.37% of all nitrogen atoms, respectively. The (M+1)+• peak arises from the incorporation of the less abundant isotope, ¹⁵N.

To determine its expected percent abundance, we use a straightforward formula: the abundance of the less common isotope divided by the total abundance of isotopes, multiplied by 100. For the compound in question, this calculation results in an anticipated 0.37% for the (M+1)+• peak.

Understanding the isotopic composition is crucial in mass spectrometry analysis, as it enables the differentiation of molecular structures based on their unique isotopic patterns. The calculation provides insights into the relative abundance of isotopic variants, aiding researchers in identifying and characterizing compounds. In this context, the 0.37% abundance for the (M+1)+• peak highlights the contribution of the ¹⁵N isotope to the overall mass spectrum, emphasizing the significance of isotopic considerations in accurate mass spectrometric analysis.