In mass spectrometry, where would singly charged and doubly charged ions of Ca-40 appear on the spectrum, given that singly charged Ca is listed first?

In mass spectrometry, where would singly charged and doubly charged ions of Ca-40 appear on the spectrum, given that singly charged Ca is listed first?

• A. 40 and 20
• B. 40 and 60
• C. 40 and 80
• D. 40 and 40

Answer: (A)

In mass spectrometry, peaks appear at masses-to-charge ratios (m/z). The mass of Ca-40 is about 40 Da. If it is singly charged (Ca-40+ with +1 charge), the m/z is roughly 40/1 = 40. If it is doubly charged (Ca-40 with +2 charge), the m/z is 40/2 = 20. So the spectrum will show peaks at 40 and 20, with the singly charged ion appearing at the higher m/z value. The doubled charge state pulls the peak down to half the m/z because the mass is distributed over more charge.

In mass spectrometry, peaks appear at masses-to-charge ratios (m/z). The mass of Ca-40 is about 40 Da. If it is singly charged (Ca-40+ with +1 charge), the m/z is roughly 40/1 = 40. If it is doubly charged (Ca-40 with +2 charge), the m/z is 40/2 = 20. So the spectrum will show peaks at 40 and 20, with the singly charged ion appearing at the higher m/z value. The doubled charge state pulls the peak down to half the m/z because the mass is distributed over more charge.