The goal of these online mass spectrometry exercises is to facilitate understanding of the basic ideas about monoisotopic mass, charge, molecular formula, and isotopic distribution. Finally, there is an exercise about structural characterization via different electron impact spectra. For every question each student can validate the correct answer. Don’t hesitate to contact us if you want to share your exercises as well. You can also subscribe to our MS doctoral school “mass spectrometry, principles and applications”, dedicated to EPFL phD students.
Determine the charge of the observed molecular ion.
Find the molecular formula of unknown peaks.
Find the monoisotopic mass of peptides from the protonated species.
Find the atom composition that fits the isotopic distribution.
Assign electronic impact mass spectra to the corresponding molecule.
Our MS doctoral school is dedicated to phD students who need to improve their knowledge in mass spectrometry.
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How to use our Mass Spectrometry Excercises

Excercise 1

Charge in Mass Spectrometry

Determine the charge of the observed molecular ion. Depending on the ionization method a molecule can be charged many times. In those examples we only consider positively charged molecules. Based on the theoretical mass spectrum and the difference of mass between isotopologues, determine the charge of the observed molecular ion. Write your answer in the charge column. If it turns green…your answer is correct

Excercise 2

Molecular formula determination

The goal of this exercise is to find the molecular formula of unknown products that fits in the generale molecular formula: [C0-100 H0-100 N0-5 O0-10 F0-3 Cl0-3 Br0-3 S0-3]. You will find the simulated spectra with a specified precision and the ion source used. You will fin different candidates but this exercise does not end here. To find out the final molecular formula you must use the isotopic distribution, the fine structure (mass defect) (monoisotopic mass + 1) to check if we have nitrogen and sulfur or the unsaturation degree to find out if the molecule is realistic. Have fun! Green raw means that your answer is correct

Excercise 3

Find the monoisotopic mass

The goal of this exercise is to find the monoisotopic mass of peptides composed of proteogenic amino acids.The monoisotopic mass should be given in a precision range of 0.1. The analysis has been done by electrospray (ESI) but the number of times the molecule has been protonated is unknown ! Last tip: You should not forget that by ESI we add protons on the peptide and also that the monoisotopic mass is not always the most abundant peak

Excercise 4

Isotopic pattern exercise

In this exercice you need to find the atom composition that fits the isotopic pattern. You may use between one and three atoms to reach the pattern, among C, S, Cl and Br. Ignore X axis absolute value. Once you are done, you may click on the button “Show answers” to display the correct result. Once your answer is correct, the raw changes green.

Excercise 5

Fragmentations by electron impact

In those exercises you should assign each electron impact mass spectrum (EI 70ev) to the corresponding molecule. For each exercise you receive a set of spectra and the corresponding molecules. You should first select an exercise, then click on one line to display the spectrum and finally click on the corresponding molecule for this spectrum. In some cases, please note that electron impact structure identification has some limitations: in some cases you can really not distinguish between 2 products ! You will have to try both possibilities .