What is the charge of an ionized peptide in the mass spectro

What is the charge of an ionized peptide in the mass spectrometer if its isotopic peaks are 0.25 m/z apart?
a. 0.25+
b. 2.5+
c. 0.4+
d. 4.0+

What is the uncharged mass of a peptide with a measured m/z of 3662.1 and a 3+ charge?
a. 10983.3
b. 10986.3
c. 3662.1
d. 3659.1

please explain?

Solution

For the m/z to be 0.25, it means the ratio is ¼ = 0.25, which means nothing else but that the charge is 4 times the mass. As the mass can’t be less than one, the mass of at least one proton, other options except 4.0+ are not possible. Answer is thus ‘d’.

Mass = m/z x z = 3662.1 x 3 = 10986.3