a) Calculate the accurate mass of the following ions:

The exact (or accurate) mass of a positive ion formed by the removal of one or more electrons from a molecule is equal to its monoisotopic mass minus the mass of the electron(s). For negative ions, the electron mass (0.000548 u) has to be added accordingly. Use accurate mass values from Table 3.1 or from the Appendix Section:

HI+.
1.007825 u + 129.904468 u – 0.000548 u = 130.911745 u

H2O+.
2 * 1.007825 u + 15.994915 u – 0.00548 u = 18.010017 u

C6H12+.
6 * 12 u + 12 * 1.007825 u – 0.000548 u = 84.093352

b) Is a resolution of R = 5000 sufficient to separate C5H9+ from CF3+ ions?

First, one has to calculate the accurate masses of both ions. Then the relationship R = m / Δm can be used to ckeck the resolution (if you don’t know the meaning of resolution see Chap. 3.4):

C5H9+:   5 * 12 u + 9 * 1.007825 u – 0.000548 u = 69.069877 u

CF3+:     12u + 3 * 18.998403 u – 0.00548 u = 68.994661 u

Thus we obtain

R = 69 u / (69.069877 – 68.994661) u = 917

i.e., R = 1000 readily separates these isobaric ions.