Figure 1. MS and MS/MS of MMAE.

(a) To define the MS and MS/MS analyses of MMAE, the matrix, CHCA in 75% acetonitrile, 0.02% trifluoroacetic acid, 2.0-mM sodium acetate and a 1/1000 dilution of aniline (10 mg/mL, 1.0 μL) was used for the ionization of the MMAE standard (1.0 μM, 1.0 μL). [M + H]⁺, [M + Na]⁺, and [M + K]⁺ were m/z 718.4, 740.4, and 756.4, respectively. (b) The MMAE-specific MS/MS fragment, m/z 496.3, was determined when [M + Na]⁺ was used as a precursor ion in the MS/MS analysis.