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