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Organic Compound Mass Spectrometry - Database of Ions

Database of m/z values for ions produced in mass spectrometry (this page)

Designed for Advanced level pre-university/college organic chemistry students

[Author © Dr Phil Brown PhD: Doc Brown's advanced level organic chemistry exam revision notes on mass spectrometry suitable for students of UK based A level and IB chemistry courses & US K12 grade 11, grade 12 and AP honors chemistry courses [updated Mar 6th 2026 *]

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Database of m/z values for ions produced in mass spectrometry (this page)

15.1.0 An introduction to mass spectrometry and its applications

(written before the extra sections and links below, so, some overlap!)

15.1.1 Index of mass spectra of organic compounds

15.1.2 Mass spectrometry applied to organic molecules - interpreting spectra - fragmentation patterns

15.1.3 More on the uses and applications of mass spectrometry, mainly in organic chemistry

15.1.4 Database of accurate m/z values and possible identity of ions formed in mass spectrometry  (THIS PAGE)

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Sub-index for this page 15.1.4 Data base of m/z ions for mass spectrometry

15.1.4 Database of m/z values and possible ions

(a) Relative accurate isotopic masses (= to four decimal places and % abundance)

(b) m/z values and possible formula-structure of the mono-positive ion

(c) Possible permutation ratios based on the isotopes of chlorine and/or bromine in organic halogen compounds

(a) Relative accurate isotopic masses (= to four decimal places and % abundance)

1H = 1.0078  and  2H = 2.0141 (0.01%)

12C = 12.0000  (standard) and  13C = 13.0034 (1.1%)

14N = 14.0031  and 15N = 15.0001 (0.37%)

16O = 15.9949  and  17O = 16.9991 (0.037%)  and 18O = 17.9992 (0.2%)

19F = 18.9984 (100%)

32S = 31.9271 (~95%) and 34S = 33.9679 (~4%)

35Cl = 34.9689 (75.8%)  and  37Cl = 36.9659 (24.2%)

79Br = 78.9183 (50.7%)  and 81Br = 80.9163 (49.3%)

127I = 126.9045 (100%)

PLEASE NOTE that the relative electron mass = 0.0005, BUT has not been deducted from the accurate m/z values listed below, but the software of a modern mass spectrometer will do so automatically!

Note that an accurate mass spectrometer can sort out ions with the same integer m/z value because they can measure relative fragment ion masses to four decimal places. and I've quoted some examples.

mass spectrometry index

(b) m/z values and possible formula-structure of the mono-positive ion

This is a data table of possible ion structure-formula for integer m/z values of ions formed in mass spectrometers and is designed for advanced level pre-university chemistry students

Unless otherwise indicated, assume C in the formula means the 12C isotope for carbon.

I have included some ions containing a 13C isotope atom.

Similarly, assume oxygen is 16O and nitrogen is 14C.

m/z 1: [H]+ 

m/z 2: [H2]+

m/z 13: [CH]+

m/z 14: [CH2]+

m/z 15: [CH3]+

m/z 16: [O]+ = 16 (15.9949)  *  [CH4]+ = 16 (16.0312)  *  [NH2]+

m/z 17: [OH]+  *  [NH3]+

m/z 18: [H2O]+

m/z 19: [F]+. [H3O]+

m/z 25: [C2H]+

m/z 26: [C2H2]+ = 26.0156  *  [CN]+ = 26.0031

m/z 27: [C2H3]+ = 27.0234  *  [CHN]+ = 27.0109

m/z 28: [CO]+ = 27.9949  *  [CH2=CH2]+ = [CH2CH2]+ = [C2H4]+ = 28.0312  *  [CH2N]+ = 28.0187  *  [N2]+, = 28.0062

m/z 29: [CHO]+ = 29.0027  *  [C2H5]+ = 29.0390 *  [13C12CH4]+ = 29.0346  *   [CH3N]+ = 29.0265

m/z 30: [13C12CH5]+ = 30.0424  *  [C2H6]+ = 30.0468  * [H2C=O]+ = 30.0105  *  [CH4N]+ or [CH2NH2]+ = 30.0343  *  [NO]+ = 29.9998

m/z 31: [CH3O]+

m/z 32: [O2]+ = 31.9898  *  [CH4O]+ or  [CH3OH]+ = 32.0261

m/z 33: [HS]+,

m/z 34: [H2S]+

m/z 35: [35Cl]+

m/z 36: [H35Cl]+

m/z 37: [C3H]+  = 37.0078  *  [37Cl]+ = 36.9659

m/z 38: [C3H2]+ = 38.0156  * [H37Cl]+ = 37.9737

m/z 39: [C3H3]+ = 39.0234

m/z 40: [13C12C2H3]+ =  40.0268, [C3H4]+ = 40.0312  *  [CH2CN]+ or [C2H2N]+ = 40.0187

m/z 41: [C3H5]+ = 41.0390  and [C2H3N]+ = 41.0265

m/z 42: [C3H6]+  = 42.0468  and  [13C12C2H5]+ =  42.0424  *  [C2H2O]+ = 42.0105  *  [C2H4N]+ = 42.0343

m/z 43: [C2H3O]+ or [CH3C=O]+ = 43.0183  *  [C3H7]+ = 43.0546  *  [C2H5N]+ = 43.0421   *  [13C12C2H6]+ = 43.0502  *  [CHNO]+ = 43.0058

m/z 44: [C3H8]+ = 44.0624  *  [13C12C2H7]+ = 44.0580  *  [CO2]+ = 43.9898  *  [C2H4O]+ = 44.0261  * [13C12CH3O]+ = 44.0217  *  [CH3CHNH2]+ = [C2H6N]+ = 44.0499 * [CH2NO]+ or  [O=C-NH2]+ = 44.0136  *

m/z 45: [COOH]+ = 44.9976  *  [CH2OCH3]+ or [CH3CHOH]+ or [C2H5O]+ = 45.0339  * [13C12CH6N]+ = 45.0533  *  [C2H7N]+ = 45.0577  *  [13C12CH4O]+ = 45.0295  *  [13CH2NO]+ = 45.0170

m/z 46: [13C12CH5O]+ = 55.0502  * [C2H6O]+ = 46.0417  *  [CH2O2]+ = 46.0054  *  [NO2]+ = 45.9929

m/z 47: [CH2SH]+ or [CH3S]+

m/z 49: [CH235Cl]+

m/z 51: [C4H3]+ =?  *  [CH237Cl]+ = ?

m/z 52: [C4H4]+ 

m/z 53: [C4H5]+ = 53.0390  *  [C3HO]+ = 53.0027

m/z 55: [13C12C3H6]+ = 55.0502 * [C4H7]+ = 55.0546  *  [C3H3O]+ = 55.0183  *  [C3H5N]+ = 55.0421

m/z 56: [13C12C3H7]+ = 56.0580  * [C4H8]+ = 56.0624

m/z 57: [C4H9]+ = 57.0702  *  [C3H5O]+  = 57.0339 = [CH3CH2C=O]+  * [13C12C3H8]+ = 57.0658

m/z 58: [13C12C3H9]+ = 58.0736  *  [C4H10]+ = 58.0780  *  [C3H6O]+ = 58.0417  *  [13C12C2H5O]+ = 58.0373  *  [C3H8N]+ = 58.0655

m/z 59 [CH3CH2OCH2]+ or [C3H7O]+ = 59.0495  *  [13C12C2H6O]+ = 59.0451  *  [CH3COO]+  or  [CH3OC=O]+ or  [C2H3O2]+ = 59.0132

m/z 60: [13C12C2H7O]+ = 60.02549   *  [C3H8O]+ = 60.0213  *  [13C12C2H9N]+ = 60.0767  *  [CH4N2O]+ = 60.0323

m/z 61: [13C12C2H4O2]+ = 61.0244  *  [C2H5O2]+ = 61.0288  * [13C12C2H8O]+ = 61.0607  *  [CH3COO]+

m/z 63: [C5H3]+ = 63.0234  *  [C2H435Cl]+ = 63.0001

m/z 64: [CH3CH235Cl]+

m/z 65: [C5H5]+ = 65.0390  *  [C2H437Cl]+ = 64.9971   *  [13C12CH535Cl]+ = 65.0113

m/z 66: [CH3CH237Cl]+

m/z 67: [C5H7]+ = 67.0546  * [13C12CH537Cl]+ = 67.0083

m/z 68: [13C12C4H7]+ = 68.0580  *  [C5H8]+ = 68.0264  *  [13C12CH535Cl]+ = 65.0113

m/z 69: [C5H9]+

m/z 70: [C5H10]+

m/z 71: [13C12C4H10]+ = ?  *  [C3H7-C=O]+ = ? * [C5H11]+ = ?

m/z 72: [C5H12]+ = 72.0936  *  [13C12C4H11]+ = 72.0892  *  [C3H6NO]+

m/z 73: [13C12C4H12]+ = ?, [C4H9O]+ = ?  *  [C3H7NO]+  *  [C3H7OCH2]+  *  [C3H5O2]+ 

m/z 74: [C6H2]+  * [C4H10O]+ 

m/z 75: [C6H3]+  *  [13C12C3H10O]+

m/z 76: [C6H4]+  

m/z 77: [C6H5]+ *  [C3H635Cl]+ 

m/z 78: [C3H735Cl]+  *  [13C12C5H5]+ = 78.0424  *  [C6H6]+ = 78.0468

m/z 79: [C6H7]+  *  [79Br]+  *  [C3H637Cl]+  *  [13C12C2H735Cl]+ 

m/z 80: [C3H735Cl]+  *  [H79Br]+

m/z 81: [81Br]+  *  [13C12C2H737Cl]+  * [C6H9]+

m/z 82: [H81Br]+  *  [C6H10]+  *  [C35Cl2]+  *

m/z 84: [C6H12]+

m/z 85: [C6H13]+  *  [C4H9-C=O]+

m/z 86: [C6H14]+ = 86.1092   *   [13C12C5H13]+ = 86.1048

m/z 87:  [13C12C5H14]+

m/z 89: [C7H5]+

m/z 90: [C7H6]+ or  [C6H5-CH]+

m/z 91: [C7H7]+

m/z 92: [C7H8]+ = 92.0264   *  [13C12C6H7]+ = 92.0580  *  [C4H935Cl]+ 

m/z 93: [CH279Br]+  *  [13C12C3H935Cl]+

m/z 94: [C4H937Cl]+  *   [CH379Br]+

m/z 95: [CH281Br]+  *  [13C12C3H937Cl]+  *  [13CH379Br]+

m/z 96:  [CH381Br]+

m/z 97: [C7H13]+ 

m/z 99: [C7H15]+  *  [13CH381Br]+

m/z 100: [C7H16]+

m/z 101: [13C12C6H16]+

m/z 103: [C8H7]+

m/z 104: [C8H8]+ = 104.0624  *  [13C12C7H7]+ = 104.0580

m/z 105: [C8H9]+

m/z 106: [C8H10]+ = 106.0780  *  [13C12C7H9]+ =  106.0736  *  [13C12C5H5CO]+ = 106.0373   *  [C6H6CO]+ = 106.0417

m/z 107: [13C12C7H10]+  *  [C2H479Br]+ or [79BrCH2CH2]+

m/z 108: [C2H579Br]+

m/z 109: [C2H481Br]+ or [81BrCH2CH2]+  *  [13C12CH579Br]+

m/z 110: [C2H581Br]+

m/z 111:  [13C12CH581Br]+

m/z 112: [C6H535Cl]+

m/z 113: [13C12C5H535Cl]+

m/z 114: [C8H18]+  *  [C6H537Cl]+

m/z 115: [13C12C7H18]+  *  [13C12C5H537Cl]+

m/z 118: [C8H18]+

m/z 119: [C9H11]+

mm/z 120: [C9H12]+

m/z 121: 13C12C8H12

m/z 122: [C3H779Br]+

m/z 123: [13C12C2H779Br]+

m/z 124: [C3H781Br]+

m/z 125: [13C12C2H781Br]+

m/z 142: [79BrCH2CH235Cl]+ ?

m/z 144: [79BrCH2CH237Cl]+  *  [81BrCH2CH235Cl]+  *   [79BrCH2CH237Cl]+ = 143.9154  *  [81BrCH2CH235Cl]+ = 143.9164

m/z 146: [81BrCH2CH237Cl]+

m/z 171: [CH79Br79Br]+

m/z 173: [CH79Br81Br]+

m/z 175: [CH81Br81Br]+

m/z 186: [CH3CH79Br79Br]+

m/z 188:  [CH3CH79Br81Br]+  or  [CH3CH81Br79Br]+ 

m/z 190: [CH3CH81Br81Br]+

mass spectrometry index

(c) Possible permutation ratios based on the isotopes of chlorine and/or bromine in organic halogen compounds

Three scenarios are described covering the pairs of common isotopes of chlorine and bromine

Isotope permutation grid for dichloro compounds The approximate isotope ratios for the parent dichloro molecular ions and fragment ions for the mass spectrum of an organic halogen compound based on ~75% 35Cl and ~25% 37Cl. If R = the 'rest' of the ion (e.g. alkyl or aryl), you get a ratio for 16 permutations:

R35Cl35Cl : R35Cl37Cl : R37Cl37Cl  of 9 : 6 : 1, so look for this triple peak pattern in the mass spectrum diagram of a molecule containing two chlorine atoms.

For monochloro compounds you would simply get a twin peak ratio of approximately 3 : 1 for R35Cl : R37Cl for any RCl m/z ion.
Cl isotope 35Cl 35Cl 35Cl 37Cl
35Cl 35-35 35-35 35-35 35-37
35Cl 35-35 35-35 35-35 35-37
35Cl 35-35 35-35 35-35 35-37
37Cl 37-35 37-35 37-35 37-37

 
Isotope permutation grid for dibromo compounds The approximate isotope ratios for the parent dibromo molecular ions and fragment ions for the mass spectrum of a compound based on ~50% 79Br and ~50% 81Br. If R = the 'rest' of the ion (e.g. alkyl or aryl), you get a ratio for

R79Br79Br  :  R79Br81Br  :  R81Br81Br  of 1 : 2 : 1, so look for this twin peak pattern in the mass spectrum diagram of a compound containing two bromine atoms. 

For monobromo compounds you get a twin peak ratio of ~1 : 1 for R79Br  :  R81Br  for any RBr m/z ion.
Br isotope 79Br 81Br
79Br 79-79 79-81
81Br 81-79 81-81

 

Explaining isotopic combinations for an organic halogen compound containing one chlorine atom and one bromine atom i.e. a bromochloro compounds (from AI, but checks out with my own 'grid' calculations).

Let's go through the isotopic combinations for chlorine (Cl) and bromine (Br).

For chlorine, we have a ratio of 35Cl to 37Cl of ~3 : 1, and for bromine, 79Br to 81Br is ~1:1

  1. M (35Cl + 79Br):
    • The probability for this combination is (3/4) * (1/2) = 3/8.
  2. M+2 (35Cl + 81Br, 37Cl + 79Br):
    • The two contributions here are (3/4) * (1/2) = 3/8 and (1/4) * (1/2) = 1/8, giving us a sum of 4/8 or 1/2.
  3. M+4 (37Cl + 81Br):
    • The probability is (1/4) * (1/2) = 1/8.

Thus, the ratio is 3:4:1 for 1. : 2. : 3.

Relative abundance ratio for M, M+2, M+4 (one Cl and one Br in the same molecule)

  • Natural abundances (approximate, used as ratios):
    • ³⁵Cl : ³⁷Cl = 3 : 1 (i.e., 75% : 25%) and ⁷⁹Br : ⁸¹Br = 1 : 1 (i.e., 50% : 50%).
  • Possible molecular-ion isotopic combinations and their probabilities:
    • M (⁷⁹Br + ³⁵Cl): (3/4) × (1/2) = 3/8
    • M+2 (either ⁷⁹Br + ³⁷Cl OR ⁸¹Br + ³⁵Cl): (1/4) × (1/2) + (3/4) × (1/2) = 1/8 + 3/8 = 4/8
    • M+4 (⁸¹Br + ³⁷Cl): (1/4) × (1/2) = 1/8
  • Convert to simple whole-number ratio by dividing by 1/8:
    • 3/8 : 4/8 : 1/8 → 3 : 4 : 1

 Mass spectrometry - introduction and mass spectra index

Advanced Level Chemistry for students aged ~16-19

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of Doc Brown's pre-university advanced level chemistry website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial. These organic chemistry revision notes on spectroscopy (on a database of ions and m/z values for mass spectrometry) suitable for use of pre-university students studying AQA advanced level chemistry, Edexcel advanced level chemistry, OCR advanced level chemistry, IB advanced level chemistry, WJEC (Eduqas) advanced level chemistry, CIE advanced level chemistry, CCEA advanced level chemistry, US grade 11-12 AP honors chemistry courses and they will also prove useful to 1st year undergraduate students of chemistry.

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries & references to A level chemistry course specifications are unofficial. Website content © Dr Phil Brown 2000+. All copyrights reserved on these organic chemistry exam revision notes on identifying m/z ions from mass spectra, these A level chemistry revision notes are suitable for use of pre-university students studying AQA advanced level organic chemistry revision notes on identifying m/z ions from mass spectra, Edexcel advanced level organic chemistry revision notes on identifying m/z ions from mass spectra, OCR advanced level organic chemistry revision notes on identifying m/z ions from mass spectra, IB advanced level organic chemistry revision notes on identifying m/z ions from mass spectra, WJEC (Eduqas) advanced level organic chemistry revision notes on identifying m/z ions from mass spectra, CIE Cambridge advanced level organic chemistry revision notes on identifying m/z ions from mass spectra, CCEA advanced level organic chemistry revision notes on identifying m/z ions from mass spectra, and useful for US grade 11 grade 12 AP honors organic chemistry courses involving identifying m/z ions from mass spectra Explaining the importance of identifying m/z ions from mass spectra in organic chemistry, What you need to know about identifying m/z ions from mass spectra for organic chemistry, Explaining the use of identifying m/z ions from mass spectra knowledge in organic chemistry, Examples of identifying m/z ions from mass spectra explained when studying organic chemistry, What is the significance of identifying m/z ions from mass spectra in organic chemistry, What is the use of identifying m/z ions from mass spectra in organic chemistry  Describing and explaining the theory of identifying m/z ions from mass spectra when studying organic chemistry, exam revision notes for identifying m/z ions from mass spectra in exams, online help for identifying m/z ions from mass spectra, revision notes for identifying m/z ions from mass spectra, what do I need to learn for identifying m/z ions from mass spectra in exams? revision summary for identifying m/z ions from mass spectra, help in teaching identifying m/z ions from mass spectra, learning notes for identifying m/z ions from mass spectra, help to pass the identifying m/z ions from mass spectra exam, how to prepare for examination questions on identifying m/z ions from mass spectra?