What is the difference between average mass, ominal mass, exact mass and accurate-mass?
The average mass of an atom or molecule is just the weighted mean of the isotopes that make it up. This is the mass value used for synthetic chemistry and is usually irrelevant in mass spectrometry. For example the average mass of phenol is 94.1112 Da. However, if you are using a low resolution technique to measure a large analyte, then you would probably see a broad peak where the peak top is a measure of the average mass. This is especially true in protein mass spectrometry. The nominal mass of an analyte is the rounded total of all the most abundant isotopes that make it up. For example the nominal mass of phenol of 94 Da. The exact mass of an analyte is the total of the all the most abundant isotopes that make it up. For example the accurate mass of phenol is 94.04186 Da. This is also called the theoretical mass of an analyte. The accurate mass of an analyte is the experimentally determined mass performed in a way to determine or confirm the molecular formula. In the example in poi
