Trimethylsilyl derivatives mass spectra

Trimethylsilylation in combination with methyloxime (MO) formation is the most popular derivatization method for steroids [62, 63], and the literature contains many examples of corresponding fragmentation pathways and details of the sy and anti isomers formed with non-sterically-hindered keto groups. A typical steroid MO-TMS derivative mass spectrum is reproduced in Figure 7 for pregnenolone [64], together with an indication of the origins of the major ions. 

Fig. 3. (Top left) Chemical methods used to depolymerize the polyesters. (Top right) Thin-layer and gas-liquid chromatograms (as trimethylsilyl derivatives) of the monomer mixture obtained from the cutin of peach fruits by LiAlD4 treatment. In the thin-layer chromatogram the five major spots are, from the bottom, C18 tetraol, C16 triol, and C18 triol (unresolved), diols, and primary alcohol. Nx = C16 alcohol N2= C18 alcohol Mj = C16 diol M2 = C18 diol D = C16 triol D2 and D3 = unsaturated and saturated C18 triol, respectively, T4 and T2, unsaturated and saturated C18 tetraol, respectively. (Bottom) Mass spectrum of component D3 in the gas chromatogram. BSA = bis-N,O-trimethylsilyl acetamide...

The volatility of the trimethylsilyl derivatives of the aldonolactones and related carbohydrates has made these derivatives suitable for use in mass spectrometry.161,162 Petersson and coworkers161,162 reported the mass spectra of a variety of trimethylsilyl derivatives of aldonolactones, including the spectrum of 54. 

Similar results have been obtained with the tetra-O-trimethylsilyl derivatives of the anomers of methyl glucopyranoside, methyl galacto-pyranoside, and methyl mannopyranoside. The 17 ev mass spectrum of the tetra-O-trimethylsilylated form of the anomers of methyl glucoside are shown in Figure 7. Again the traces are similar, but intensity differences are discernible. The ratio (377/361 )i7ev has proved most useful. 

Chromatographic trace reconstructed by summing the intensities of all of the detected masses in every spectrum, and used as arbitrary units along the y axis. The x axis is the spectrum number. This is an analysis of volatile acids as trimethylsilylated derivatives from the urine of a patient suffering a metabolic disorder. If asked, the computer can indicate the retention time of every peak. The peak that is pointed out is enlarged in Figure 5.15. 

Trimethylsilyl derivatives are commonly used in GC/MS. When the molecule contains a hydroxyl, it fragments and yields (CH3)3Si+, at m/z 73, and (CH3)2Si+-OH, at m/z 75. When the molecule contains more than one (CH3)3SiO- group, an ion with mass 147 Da is systematically observed in the spectrum, even though both groups are remote from one another. This ion has the structure shown below. It is derived from the fragmentation of a complex between the ion (CH3)3Si+ and the neutral remainder of the molecule ... 

Fig. 7, (A) El mass spectrum (70 eV) of the trimethylsilylated methyl ester of 3-Neu5Ac (B) El mass spectrum (70 eV) of the pertrimethylsilylated derivative of 3-Neu5Ac.

The structure of a 1 —> 4,1 —> 6 linked trisaccharide has been elucidated from the mass spectrum of its trimethylsilyl derivative (70). In addition to the peaks resulting from the independent fragmentation of each unit, the sequential arrangement of the monosaccharides can also be deter-... 

The mass spectrum of the corresponding trimethyl-silyl ether derivative is shown in Figure lb, and an important advantage of this derivatization is immediately apparent in the prominent [M —CH3] ion at m/z 173. This ion allows the estimation of the molecular weight of the derivative in cases where a molecular ion is absent. In addition, because the fragmentation pattern is characteristic of the molecule, it may be used as a mass spectral fingerprint to confirm the identity of the GC peak, and libraries of reference spectra are readily available. Trimethylsilylation is one of the most common derivatizations in GC-MS. Further details and examples are given later in the section on silylation. 

Figure 7.9. The mass spectrum of the trimethylsilyl ether derivative of the vicinal diol prepared from methyl...

Figure 10.10. The mass spectrum of the A/-acetyl-0-trimethylsilyl ether derivative of sphinga-4,14-dienine, isolated form plasma sphingomyelin [724], (Reproduced by kind permission of the authors and of Biochemistry, and redrawn from the original paper).

FIG. 3. Chemical ionization mass spectrum (methane reagent gas) of the trimethylsilyl derivative of orotic acid in the urine of patient receiving pyrazofurin. 

Separation and identification of initial autoxidation products of ASA in MeOH were carried out, and formation of DHA was positively confirmed as the main oxidation product of ASA. Threonolactone was identified as its TMS derivative, 2,3-di-O-trimethylsilyl-L-threonolactone, by comparing its GC retention time with that of the authentic compound, and further confirmed by comparing the mass spectrum of the sample with the authentic mass spectral data reported in the literature (3). The formation of oxalic acid was similarly confirmed by GC and GC-MS analyses. These reaction products were also detected in the autoxidation of ASA monoanion as an ASA-Na salt solution in MeOH, and the formation of the same oxidation products was confirmed in the autoxidation of ASA in an aqueous solution. It was also confirmed, however, that these autoxidation reaction products of ASA were not formed from DHA. Therefore, this appears to be a new autoxidation pathway of ASA that does not proceed via DHA, and this pathway might be involved in various oxidation processes observed in food and biological systems. 

Figure 3.26. Mass spectrum of the trimethylsilyl derivative of decanol.

Although these derivatives are limited to 2-oxocarboxylic acids, their mass spectra give rise to several ions which are common to most of the compounds in the series and permit their detection by SIM (Langenbeck etal., 1977a). The mass spectrum of the trimethylsilylated quinoxalinol formed from 2-oxovaleric acid is shown in Fig. 5.19. 

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