CHARACTERIZATION OF DESERT DATE (Balanites aegyptiaca)

Mass spectrometry
Mass spectrometry (MS) provides information about the molecular weight and chemical
structure of the compound analyzed. The mass spectrometer creates charged ions from
molecules. These ions are extracted into the analyzer region of the mass spectrometer and
separated according to their mass-to-charge ratios (m/z). The separated ions are detected
and the signals are sent to the data system where the m/z ratios are stored, together with
their relative abundance, for presentation in the format of an m/z spectrum. Because of its
specific “finger-print” property, MS is very useful in qualitative analyses of unknown
compounds. MS is generally used as a detector in GC or HPLC apparatuses.
MS has played an important role in structural analysis of saponins. In early studies,
derivatization was required for using electron impact mass spectra (Tomova et al., 1974).
Later, field desorption and fast atom bombardment spectra were employed to analyze
derivatized and underivatized saponins, providing evidence about molecular mass and
sugar sequence by cleavage of glycosidic bonds (Wu et al., 1996; Wang et al., 1997). More
recently, electrospray ionization (ESI) in the positive and negative ionization mode has
become one of the most effective analytical tools for structural characterization of native
saponins (Cai et al., 2001). Multi-stage tandem mass spectroscopy (ESI-MS n ) of molecular
ions is used for detailed structural analysis of underivatized saponins (Fang et al., 1999).
The fragment ions from glycoside cleavage provide information about the mass of
aglycone, the type of the monosaccharide, and the sequence and branching of the
oligosaccharides. The fragment ions from cross-ring cleavages of sugar residues give
information about the linkages between units.
LC-MS and LC-MS/MS have shown easy and rapid methods for the identification of
saponin and sapogenin composition compared to the traditional approaches which required
extensive purification and, in the case of GC-MS, conversion of the saponins to their
corresponding sapogenins and volatile derivatives. Both the extensive purification and the
derivatization steps are time-consuming and are known to create artifacts (Muir et al.,
2000).
13