University of California, Riverside

High Resolution Mass Spectrometry Facility



Useful Accurate Masses and Mass Differences


Useful Accurate Masses or Differences for Data Interpretation

When interpreting accurate mass data, it is often possible to obtain useful information from the mass differences seen in the spectrum. Below are some common mass differences we have seen and the chemical species they represent.

If you know of others, send us a message and we can add it to this list.

Positive Ion Accurate Masses

Common Adducts 

MLi+ = 7.0160 ; MNH4+ = 18.0334; MNa+ = 22.9898 ; MK+ = 38.9637

Common Mass Differences

Δ MNH4+ and MNa+ = 4.9559

Δ MH+ and MNa+ = 21.9823

Δ MH+ and MLi+   = 6.0082

Δ MH+ and MNH4+ = 17.0265

Δ MLi+ and MNa+ = 15.9738

Δ MNa+  and MK+ = 15.9739

Add 2 Hydrogen atoms = 2.0156

extra Oxygen = 15.9949               extra water (H 2 O) = 18.0106                  extra OH = 17.0027

extra OH that adducts Na+  this adds 39.9925 to proposed mass

extra CH2 = 14.0157                     extra CH3 = 15.0235

extra CO = 27.9949                    vs extra C2 H4 = 28.0313                      vs extra N2 = 28.0061

Δ NO2 = 45.9929

PEG Repeat Unit = (C2 H4 O1) = 44.0262

PPG Repeat Unit = (C3 H8 O1) = 58.0419

Polysiloxane Repeat Unit (C2 H6 O1 Si1) = 74.0188

Δ 35Cl and 37Cl = 1.9970

Δ 79BR and 81Br = 1.9980

 

Protecting/Blocking/Substituent Groups

tBoc = (C5 H9 O2)   101.0603

Tos = (C7 H7 O2 S1) = 155.0167

FMOC = (C15 H11 O2) = 223.0759

mmTr = (C20 H17 O1) = 273.1279

DMT (C21 H19 O2) = 303.1385

 

Solvent Related Ions

Methanol adducts adds CH3 OH = 32.0262

Triethylamine (C2 H5)3 NH+ = 102.1283

DMSO dimer = 157.0357

D6  – DMSO = 169.1110

IPA (isopropanol dimer) = 121.1229

THF dimer = 145.1228

Ethyl acetate dimer = 177.1127

Acetone dimer = 117.0916

 

Known Impurities from Various Sources

Erucamide (C22 H43 N1 O1) MH+ = 338.3423
Source – this is an anti slip agent used in polyethylene and polypropylene

Dinonacontylamine (C38 H79 N1) MH+ = 550.6291
Source – used to formulate certain rubbers used in stoppers for example

Dioctyl Phthalate (C24 H38 O4) MH+ = 391.2824, MNa+ = 413.2668
Source – a common stabilizer used in a variety of plastics

Bibutyl phthalate (C16 H23 O4) MH+ = 279.1596, MNa+ = 301.1416
Source – similar to above

Dimethicone MH+ = 371.1012
Source – hair shampoo, deodarant, corrosion inhibitor






Negative Ions Accurate Masses

Trifluroacetate (TFA) CF3 CO2 - = 112.9850; dimer = 226.9779
Source - common buffer

More Information

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Tel: (951) 827-1012

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High Resolution Mass Spectrometry Facility
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Tel: (951) 827-5287
Fax: (951) 827-4713
E-mail: Jie.Zhou@ucr.edu

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