Metastable ions arising from pseudomolecular [M-H]- ions produced by fast-atom bombardment negative-ion mass spectrometry of ecdysteroids.

Metastable ions arising from pseudomolecular [M-H]- ions produced by fast-atom bombardment negative-ion mass spectrometry of a range of free ecdysteroids, ecdysteroid conjugates and polar metabolites were investigated by means of linked scanning at constant B/E. Free ecdysteroids displayed daughter-ion spectra which allow 20-hydroxyecdysteroids and ecdysteroids lacking C-20 hydroxylation to be readily distinguished. The ejection of acetic acid from acetylated ecdysteroids was also readily detectable. Characteristic metastable-ion decomposition of ecdysteroid acids was not observed, presumably as a result of charge localization. High-mass daughter ions were also lacking in the case of phosphate conjugates.