Confirmation of the structure of lipid A derived from the lipopolysaccharide of Rhodobacter sphaeroides by a combination of MALDI, LSIMS, and tandem mass spectrometry

The chemical structure of nontoxic diphosphoryl lipid A from Rhodobacter sphaeroides was confirmed using a combination of LSIMS (on a two-sector mass spectrometer) and MALDI (on time-of-flight and ion trap mass spectrometers) in conjunction with tandem mass spectrometry in both positive and negative ion modes. Accurate molecular weight measurement accompanied by the analysis of fragment ion masses yielded the composition of fatty acyl groups. Tandem experiments (collisionally induced dissociation of both quasimolecular and oxonium ions) were also performed, revealing the precise location and nature of the fatty acyl groups on the disaccharide backbone.