Figure 5.29 MALDI-TOF mass spectrum of insulin and β-lactoglobulin. A mixture of 5 pmol each of insulin (I) and β-lactoglobulin (L) was ionized by MaLDI, which produces predominately singly charged molecular ions from peptides and proteins—the insulin ion (I + h)⁺ and the lactoglobulin ion (L + h)⁺. Molecules with multiple charges, such as those for β-lactoglobulin indicated by the blue arrows, as well as small quantities of a singly charged dimer of insulin (2 I + h)⁺, also are produced.