Steroid fragment ions

Fragmentation of suitable C(3)-substituted 4,4-dimethyl steroids (18) is characterized by the loss of either the ion (19), or the radical (21), which leaves a steroidal fragment ion (22) of characteristic mass. The A - and A < >-unsaturated compounds are particularly prone to fragmentations of this type. 

FIGURE 14.3 Some important steroid fragment ions observed in El spectra. 

The enhanced loss of CH3 from the 5P isomer is explained in terms of the lower critical energy for this reaction cf. the 5a-isomer) due to the increased steric strain at the A/B ring junction. It has further been shown 38) that steroid epimers show differences in their collisionally activated dissociation spectra. In this study, steroid fragment ions were employed as targets for collision. 

Molecular ion Molecular ions of cyclic ketones are relatively intense. Characteristic fragment ions of cyclic ketones occur ai m/z 28, 29, 41, and 55. Cyclic ketones also lose CO and/or C>H (m/z 28) from the molecular ion (Q and higher). Low-abundance ions corresponding to loss of H20 are frequently observed. Keto-steroids are a special class of cyclic ketones and have abundani molecular ions. 

B. Characteristic Fragment Ions The most characteristic cleavage is the loss of carbons 15,16, and 17, together with the side chain and one additional hydrogen. It is possible to determine the elemental composition of the side chains of steroids by the difference in the mass between the molecular ion and an intense ion more than 15... 

Steroids such as progesterone, testosterone, and cortisone have been derivatized and analyzed with this method. Cortisone was chosen to demonstrate the enhanced sensitivity obtained with the derivatization/SIMS technique. The SIMS results for underivatized and derivatized cortisone are presented in Figure 10. The ions that are observed from cortisone include the molecular ion [M + H]+ (m/z 361), the silver cationized ion [M + Ag]+ (m/z 467 and 469), and the fragment ion at m/z 407 and 409 corresponding to the loss of the OCHCH2OH group. 

Ionized primary enamines of low energy may also be reaction intermediates in the loss of ammonia. Scheme 34 shows a mechanism proposed for the extensive loss of ammonia from low-energy ionized 3-amino steroids. Enamine 63 may lose ammonia after two successive 1,4 H-transfers. The participation of the H at C(5) has been established by D-labelling42. Only higher energy ions lead to m/z 82 fragment ions through the ionized dienamine 64,... 

This stndy demonstrates the difficulties faced in identifying fragment ions in the MS-MS spectra of steroids. Therefore, the use of diagnostic ions is more practical in confirmation. In some cases, diagnostic ions do not allow an unambiguous confirmation of identity, especially in the differentiation between isomers. 

Sjoberg and Markides [46] applied the relative abundances of water-loss-related fragment ions in energy-resolved in-source CID or collision-cell CID to differentiate between isomeric hydroxy steroids. As an example, the relative abundance ratio of [M+H-HjO] and [M+H-2H20] is plotted as a function of the collision energy for 5oc-androstane-3p,17P diol and 5a-androstane-3oc,17P diol inFigure 13.6. 

The search for the precursors of abundant fragment ions in the El spectra of different A -3-keto steroids leads to the almost complete interpretation of the spectra (Table 14). Figure 47 summarizes these fragmentations, largely due to rings A and B cleavage. 

Precursors of fragment ions formed in El from various A -3-keto steroids by HV scan spectra [201]... 

Fig. 3. Diagnostic fragment ions for the spirostanol and furostanol A5-steroid saponins...

TABLE 14.2 Common Fragment Ions and Losses Observed in the Mass Spectra of Trimethylsilyl and MO Derivatives of Ci, and C21 Steroids... 

TABLE 14.4 Characteristic Fragment Ions Observed i Derivatized 3-oxo-4 ene (3-oxo-A ) Steroids n the CID Spectra of [M+H] and [M] Ions from Protonated and ... 

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