Calculating the Theoretical Average Mass for an Intact Protein in BioPharmaView™ Software

For research use only. Not for use in diagnostic procedures.

Answer

A protein's molecular weight can be calculated by adding the average isotopic masses of amino acids in the protein and the average isotopic mass of one water molecule. Molecular weight values are given in Dalton (Da).

However slight theoretical average mass differences compared to other software packages do occur, and these might depend on which isotopes are being used as the most abundant isotope when calculating the average MW.

The isotope abundances vary from place to place, so there’s no absolute value for the isotopic composition, but BioPharmaView™ software uses the isotopic masses published by NIST online at: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl
Please note that the results generated will be the same throughout all SCIEX software (e.g., PeakView™ and ProteinPilot™ software).
 
SCIEX updated the isotopic composition values to the currently published NIST values, which changed the MW for antibodies by a Dalton or two.

Note: More information was provided on the NIST website regarding their published abundances here:
In the opinion of the Subcommittee for Isotopic Abundance Measurements (SIAM), these values represent the isotopic composition of the chemicals and/or materials most commonly encountered in the laboratory. They may not, therefore, correspond to the most abundant natural material.