FABMS/MS

The analysis of samples in biological matrices is extremely powerful compared with drawbacks such as narrow concentration range for quantitative measurements and long time required for spot detection. Digital autoradiography can be used in hyphenated off-line and online methods. A powerful example is TLC/DAR/FABMS/MS with applications in in vitro and in vivo metabolism studies. 

NMR data of 47, including the H H COSY, HOHAHA, HMQC, and HMBC spectra, and the FABMS/MS fragmentation, corroborated well with those of the imine (C-20 and N) form of 46. The treatment of 47 with NaBH4 afforded senepodine A (46) by... 

Figure 12. Fragmentation patterns observed in positive ion FABMS/MS spectrum of himeradine A (56) (precursor ion mjz 452) (42).

A convincing body of experimental, information, now available in the literature, serves as confirmation for the possibility to desorb molecular ions out of the condensed phase even for organic molecules which are generally considered nonvolatile and/or fragile and do therefore not lend themselves to classical mass spectrometric analysis. Here the laser-MS competes with techniques such as static SIMS or FABMS, plasma- and field-desorption. 

Figure 1.14 displays an example of FABMS and MS/MS applied to the detection of peptides in a mixture and the sequence determination of one of them. 

References are given for spectroscopic studies, other v,c-oi IR hen these studies are reported in the synthetic/structural reference no further reference number is given. MS, mass spectrum FABMS, fast atom bombardment mass spectrum VT, variable-temperature. 

Sisunine (302) was isolated from a clone of a hybrid Solanum acaule and S. x ajanhuiri [675]. The structure of 302 was determined by FABMS, GC-MS, and acid hydrolysis to give galactose, glucose, and tomatidine (298). Sisunine formation was the result of independent inheritance of the aglycone and saccharide moieties [675]. 

Other issues FABMS = [M-2H20+H] original MS data from HREIMS. 

Positive ion fast atom bombardment (FAB) mass spectra were obtained with the JEOL HXllO/HXllO tandem double-focusing mass spectrometer with JEOL gun and collisionally induced decomposition (CID) MS/MS. The JEOL instrument was operated at +10 kV with -20 kV postacceleration at the detector. The xenon neutral beam had 6 kV acceleration from the JEOL gun. CID MS/MS was performed with 1 1000 resolution in both MS-1 and MS-2. Helium was used as the collision gas at a pressure sufficient to reduce precursor ion abundance by 75%. Samples were dissolved in methanol-glycerol (1 1, v/v) for all FABMS analyses. 

Several methods have been developed specifically for naphthenic acids, a class which includes the surface active carboxylate surfactants. Naphthenic acids are present as a complex mixture of a number of homologues with only a small range in molar mass (166-450 mol/g), little change in solubility character, and have been difficult to assay using conventional analytical methods. Methods such as negative ion-mode mass spectrometry using fast atom bombardment (FABMS), have been successfully applied to the analysis of naphthenic acid mixtures [93, 94], Other promising techniques include fluoride ion chemical ionization mass spectrometry (FI-MS) [95], and electrospray ionization mass spectrometry (ESIMS), which may allow for the quantification of the various naphthenic acid fractions [96]. 

Other types of mass spectrometry such as FDMS, FABMS, and HRESlET MS that can produce useful information about the molecular weight, elemental composition, and binding sequence of monosaccharide units in the glycoside carbohydrate chain have been broadly applied in addition to ElMS. 

High performance liquid chromatography is well established as a tool for the separation of mixtures of labile biological substances, but its combination with mass spectrometry (LC/MS) remains fraught with difficulties as a valid analytical procedure. Several new types of direct liquid introduction interfaces (as opposed to transport interfaces) have been developed recently and appear to offer promise for the future. The thermospray interface 44) has been used successfully for amino acids, small peptides, nucleosides, antibiotics and glucuronides. The spectra are the relatively simple ones commonly obtained from soft ionization methods and resemble those obtained by FABMS. A gas nebulizer interface has enabled representative spectra (resembling those generated from DCI) to be... 

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