If ionization takes place in the presence of contaminants or additives, such as ammonium or sodium ions, some compounds are susceptible to adduct formation. These spectra show other ions in addition to, or instead of, the molecular ion (see the following figure).
NOTE
The Data Viewer application can automatically add m/z annotations to the mass spectrum peaks.
The following table lists common adducts for the positive and negative ESI modes.
Cationized adducts (positive mode) | Anionized adducts (negative mode) | ||
|---|---|---|---|
[M+NH4]+ | M+18 | [M+CH3COO]– | M+18 |
[M+Na]+ | M+23 | [M+Na]– | M+21 |
[M+CH3OH+H]+ | M+33 | [M+Cl]– | M+35 |
[M+K]+ | M+39 | [M+K]– | M+37 |
[M+CH3CN+H]+ | M+42 | [M+HCOO]– | M+59 |
When determining molecular masses, take care to account for possible adduct ions.