Bad and Poor Losses

Bad and Poor Losses

Bad losses can almost always be rejected on chemical grounds. The bad loss list is established for C, H, N, O, Al, Si, P, S, F, Cl, Br, and I containing compounds. For example, CH radical has a mass of 13 Da, but is not normally found as a loss in mass spectra. CH₃ radical, with a mass of 15, on the other hand is frequently observed. As another example, no combination of elements has a mass of 10 Da that has a chemically meaningful structure with normal valences. BeH radical has a mass of 10 Da, but we are assuming that you aren't working with Be.

Poor losses are generally of low probability. However, poor losses can't be rejected on chemical grounds. For example, a loss of 82 from the molecular ion is unlikely. However, H⁸¹Br has a mass of 82 Da. This mass is in the unlikely list however, because 82 Da occurs as a loss from the M+2 isotope peak and not the molecular ion.

Bad Losses

4-13 21-23 24-26 37 38 50-53 65 66

Poor Losses

19 39 40 54 62 64 67 68 70 82 83 84 86 88 89 90 91 92 93 94 95 96 98 99 103 104 105 107 108 109 110

References:
1. Robert A. W. Johnstone, Malcolm E. Rose, Mass spectrometry for chemists and biochemists, 2nd. Ed., Cambridge University Press, Cambridge, Great Britain, 1996.
2. R.G. Dromey, B.G. Buchanan, D.H. Smith, J. Lederberg, and Carl Djerassi, "Applications of Artificial Intelligence for Chemical Inference. XIV. A General Method for Predicting Molecular Ions in Mass Spectra," J. Org. Chem., 40(6), 1975.

Colby College Chemistry, 1999