ESI Common Background Ions: Repeating Units
There are several good sources online, here are just a few:
- Mass spectrometry Contaminant Database
- Contamination Search Tools at the University of Leiden
- pdf document from Waters
- pdf document from NewObjective
- pdf document from Fisher Chemical
- Common Mass Spec Background Ions go to page
- UWPR_CommonMassSpecContaminants spreadsheet xls
Polydimethylcyclosiloxanes
Polydimethylcyclosiloxanes, widespread compound in industrial products, e.g. deodorants. They are ubiquitously present in ambient air. (Mass difference 74.018793)
| Polysiloxanes | |||
|---|---|---|---|
| Mono mass [M+H]+ |
+17 Da ammonium adducts |
-16 Da loss of methane |
Formula |
| 75.02607 | [(Si [CH3]2 O)1 + H]+ | ||
| 149.04486 | [(Si [CH3]2 O)2 + H]+ | ||
| 223.06366 | [(Si [CH3]2 O)3 + H]+ | ||
| 297.08245 | [(Si [CH3]2 O)4 + H]+ | ||
| 371.10124 | 388.12779 | 355.06994 | [(Si [CH3]2 O)5 + H]+ |
| 445.12003 | 462.14658 | 429.08873 | [(Si [CH3]2 O)6 + H]+ |
| 519.13883 | 536.16538 | 503.10753 | [(Si [CH3]2 O)7 + H]+ |
| 593.15762 | 610.18417 | 577.12632 | [(Si [CH3]2 O)8 + H]+ |
| 667.17641 | 684.20296 | 651.14511 | [(Si [CH3]2 O)9 + H]+ |
| 741.19521 | 758.22176 | 725.16391 | [(Si [CH3]2 O)10 + H]+ |
Repeating Units, positive mode
| Mass diff. | M or subunit | Description |
|---|---|---|
| 14.01565 | [CH2] | Alkane chains, waxes, fatty acids, methylation |
| 15.99492 | O | Oxidation |
| 18.01057 | H2O | Water clusters |
| 28.03130 | [C2H4] | Natural alkane chains such as fatty acids |
| 32.02622 | [CH3OH] | Methanol clusters |
| 41.02655 | [CH3CN] | Acetonitrile clusters |
| 42.04695 | [C3H6] | Propyl repeating units, propylation |
| 44.02622 | [C2H4O] | Polyethylene glycol, PEG (Tritons and Tween buffers) |
| 49.99681 | [CF2] | From perfluoro compounds |
| 53.00323 | NH4Cl | Ammonium chloride adducts (NH4Cl) salt adducts/clusters |
| 56.06260 | [C4H8] | Butyl repeating units, butylation |
| 57.95862 | NaCl | NaCl sodium chloride clusters (distinguish from PPG by Cl Isotope pattern) |
| 58.04187 | [C3H6O] | Polypropylene glycol (PPG), and related compounds |
| 63.00000 | NH4Cl | Salts |
| 63.03203 | [CHOONH4] | Ammonium formate adducts/clusters |
| 67.98742 | [NaHCO2] | Sodium formate clusters |
| 67.98742 | [CHOONa] | Sodium formate adducts/clusters |
| 72.03953 | OH | Replacement of OH by OSi(CH3)3 trimethylsiloxane |
| 73.93256 | KCl | KCl adducts (distinguishable by Cl isotope pattern) |
| 74.01879 | [O-Si(CH3)2] | Polysiloxane, silicone rubber polymer |
| 77.0477 | NH4Ac | Ammonium acetate salts (CH3COONH4) |
| 78.01394 | [C2H6OS] | DMSO adducts/clusters, dimethylsulfoxide solvent |
| 82.00307 | [NaCH3CO2] | Sodium acetate clusters |
| 84.05159 | [C2D6OS] | Deuterated DMSO adducts/clusters, NMR solvent |
| 106.90509 | 107Ag | 107Ag, silver clusters (MALDI) non-polar polymers, with 109Ag (~1:1) |
| 108.90476 | 109Ag | 109Ag, silver clusters (MALDI) non-polar polymers, with 107Ag ( ~1:1) |
| 113.9929 | CF3COOH | TFA (trifluoroacetic acid) adducts (CF3COOH) |
| 121.9383 | [NaClO4] | Sodium perchlorate adducts (NaClO4) |
| 135.97481 | NaCF3CO2 | Sodium TFA (trifluoroacetic acid) adducts (CF3COONa) |
| 162.05283 | [C6H10O5] | Polysaccharides (C6H10O5) |
| 226.16813 | [C12H22N2O2] | Cyclic oligomers from polyamide 66 (series observed with m/z 453, 679, 905); Nylon HPLC solvent filters can produce nylon (6,6monomer) peaks at masses of 226 Da a dimer 452, trimer 678 and tetramer 905 Da. The contaminant is very hard to get rid off since it binds very well to C18. |
| 259.80992 | CsI | Cesium iodide clusters, used as calibration |
| 288.1371 | [CH3(CH2)11OSO3Na] | SDS (sodium dodecylsulfate) adducts (CH3(CH2)11OSO3Na) |
Phthalates
391 and 419 are typically very prominent in ESI
| Avg Mass | Exact Mass | M or subunit | Description |
|---|---|---|---|
| 195.0652 | 194.05736 | C6H4(COOCH3)2 | ( DMP ) Dimethyl phthalate |
| 223.0965 | 222.08866 | C6H4(COOC2H5)2 | ( DEP ) Diethyl phthalate |
| 247.0965 | 246.08866 | C6H4(COOCH2CH=CH2)2 | ( DAP ) Diallyl phthalate |
| 251.1278 | 250.11996 | C6H4(COO(CH2)2CH3)2 | ( DPP ) Di-n-propyl phthalate |
| 279.1591 | 278.15126 | C6H4(COO(CH2)3CH3)2 | ( DBP ) Di-n-butyl phthalate |
| 279.1591 | 278.15126 | C6H4(COOCH2CH(CH3)2)2 | ( DIBP ) Diisobutyl phthalate |
| 305.1747 | 304.16691 | CH3(CH2)3OOCC6H4COOC6H11 | ( BCP ) Butyl cyclohexyl phthalate |
| 307.1904 | 306.18256 | C6H4(COO(CH2)4CH3)2 | ( DNPP ) Di-n-pentyl phthalate |
| 331.1904 | 330.18256 | C6H4(COOC6H11)2 | ( DCP ) Dicyclohexyl phthalate |
| 313.1434 | 312.13561 | CH3(CH2)3OOCC6H4COOCH2C6H5 | ( BBP ) Butyl benzyl phthalate |
| 335.2217 | 334.21386 | C6H4(COO(CH2)5CH3)2 | ( DNHP ) Di-n-hexyl phthalate |
| 335.2217 | 334.21386 | C6H4(COO(CH2)3CH(CH3)2)2 | ( DIHxP ) Diisohexyl phthalate |
| 363.253 | 362.24516 | C6H4(COO(CH2)4CH(CH3)2)2 | ( DIHpP ) Diisoheptyl phthalate |
| 363.253 | 362.24516 | CH3(CH2)3OOCC6H4COO(CH2)9CH3 | ( BDP ) Butyl decyl phthalate |
| 391.2843 | 390.27646 | C6H4(COOCH2CH(C2H5)(CH2)3CH3)2 | ( DEHP, DOP ) Di(2-ethylhexyl) phthalate |
| 391.2843 | 390.27646 | C6H4(COO(CH2)7CH3)2 | ( DNOP ) Di(n-octyl) phthalate |
| 391.2843 | 390.27646 | C6H4(COO(CH2)5CH(CH3)2)2 | ( DIOP ) Diisooctyl phthalate |
| 419.3156 | 418.30776 | CH3(CH2)7OOCC6H4COO(CH2)9CH3 | ( ODP ) n-Octyl n-decyl phthalate |
| 419.3156 | 418.30776 | C6H4(COO(CH2)6CH(CH3)2)2 | ( DINP ) Diisononyl phthalate |
| 447.3469 | 446.33906 | C6H4(COO(CH2)7CH(CH3)2)2 | ( DIDP ) Diisodecyl phthalate |
| 475.3782 | 474.37036 | C6H4(COO(CH2)10CH3)2 | ( DUP ) Diundecyl phthalate |
| 475.3782 | 474.37036 | C6H4(COO(CH2)8CH(CH3)2)2 | ( DIUP ) Diisoundecyl phthalate |
| 531.4408 | 530.43296 | C6H4(COO(CH2)12CH3)2 | ( DTDP ) Ditridecyl phthalate |
| 531.4408 | 530.43296 | C6H4(COO(CH2)10CH(CH3)2)2 | ( DIUP ) Diisotridecyl phthalate |