average mass

The average mass of an ion of a known empirical formula is calculated by summing the relative average atomic mass of each atom present. For example, carbon has an average atomic mass of 12.01115 Da, hydrogen is 1.00797 Da, and so on. The average mass of the molecular ion of a chemical compound is also the mass that appears on the bottle. However, in a stick representation of a mass spectrum, there is no ion signal at the average mass. Instead, signals appear for ions of various isotopic compositions. The average mass corresponds to the center of the centroid signal recorded for higher mass ions at lower instrumental resolutions.