Chemical Analysis - MS Isotopic Abundance (10.5)

Question 1

In terms of isotope analysis, what info can mass spectrometry give?

Answer 1

• info about the type + abundance of isotopes in a molecule

Question 2

What is an isotope?

Answer 2

• an atom with the same number of protons but a different number of neutrons

Question 3

What is special about bromine?

Answer 3

• has 2 isotopes (79 & 81)
• relative abundanices of the 2 isotopes = roughly 50:50
• if you see two molecular ion peaks with a 1:1 ratio, separated by two mass units there is likely to be bromine present

Question 4

Why is natural vanilla more expensive than synthetic vanilla?

Answer 4

• relative abundances of different isotopes in a molecule can give valuable information about a sample
• plants preferably absorb 12CO2 over 13CO2, so natural vanilla has a lower ratio of 13CO2

Question 5

What is the relative atomic mass (Ar)?

Answer 5

• the weighted average mass of atoms of an element on a scale in which a C-12 atom has a mass of exactly 12

Question 6

What is the formula for relative atomic mass?

Answer 6

RAM = Sum of: (mass of isotope x isotopic abundance)/100

Question 7

How do you calculate isotopic abundance?

Answer 7

RMA = Sum of: (X x Y)/100
x + y = 100
x = 100 - y
Then rearrange to find the percentages