Mass spectrometric identification and confirmation of 16-methylprednisone acetate in Mexican pills

The identification and confirmation of an unusual corticosteroid, 16-methylprednisone acetate, in Mexican pills is described. Identification is based on molecular structure illucidation from the electron impact fragmentation pattern. Characteristic m/e peaks at 121 (base peak), 241, 256 and 414 (molecular ion) are observed. Fragmentation pathways leading to these ions are presented. Confirmatory studies, employing NMR are also presented.