The Kendrick mass is defined by setting the mass of a chosen molecular fragment, typically CH2, to an integer value in atomic mass units. It is different from the IUPAC definition, which is based on setting the mass of 12C isotope to exactly 12 u. The Kendrick mass is often used to identify homologous compounds differing only by a number of base units in high resolution mass spectra. This definition of mass was first suggested in 1963 by chemist Edward Kendrick, and it has been adopted by scientists working in the area of high-resolution mass spectrometry, environmental analysis, proteomics, petroleomics, metabolomics, etc.
According to the procedure outlined by Kendrick, the mass of CH2 is defined as exactly 14 Da, instead of the IUPAC mass of 14.01565 Da.
To convert an IUPAC mass of a particular compound to the Kendrick mass, the equation
is used. The mass in dalton units (Da) can be converted to the Kendrick scale by dividing by 1.0011178.
Other groups of atoms in addition to CH2 can be used define the Kendrick mass, for example CO2, H2, H2O, and O. In this case, the Kendrick mass for a family of compounds F is given by