Isotopic Distributions in Mass Spectra of Large Molecules

Molecular ion distributions are calculated and presented for three sets of homologues with different elemental compositions and hence different mass defects and isotopic distributions in the 1000, 10 000, and 100 000 amu mass ranges. The usefulness is examined of different values characteristic of molecular weights: nominal mass, monoisotopic mass, most abundant mass, and average mass. Experimental problems are described which affect the determination of average molecular weights in the mass range 3000–4000 amu.