Characterization of castor bean neutral lipids by mass spectrometry/mass spectrometry
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A method has been developed for the characterization of intact neutral lipids isolated from castor bean (Ricinus communis L.) by mass spectrometry/mass spectrometry (MS/MS). The molecular weights of the trimethylsilyl (TMS) derivatives of the neutral lipids are determined by using both electron impact and chemical ionization (ammonia). Collision-induced dissociation daughter spectra of the (M-CH3)+ ions yield fragment ions that allow easy determination of the acyloxy groups present. The chainlength and degree of unsaturation for each acyloxy group are indicated by R in the ion represented by the general formula (RCO + 74)+. Other ions of diagnostic value include (M-RCOO)+, (M-RCOOH)+, [(M-CH3-RCOOH]+ and [(M-RCOOH)-16]+. The presence of a TMS group in any of these fragments results in the formation of ions representing the loss of OTMSH. Prior to MS/MS analysis, partial fractionation by high-performance liquid chromatography (according to degree of unsaturation in the neutral lipids) is useful because daughter spectra are generated free of any isotopic contamination, and minor components are concentrated in single fractions, which aids their characterization. By using this method, 11 neutral lipids were characterized in castor bean.
Key WordsCastor bean daughter ion diacylglycerol MS MS/MS neutral lipid ricinoleic acid Ricinus communis L. triacylglycerol trimethylsilyl derivative
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