New conditions for matrix-assisted laser desorption/ionization mass spectrometry of native bacterial R-type lipopolysaccharides

A new sample preparation method for matrix-assisted laser desorption/ionization (MALDI) analysis of native rough-type lipopolysaccharides (R-type LPSs) is presented. In our MALDI mass spectra, besides the M--H](-) ions, abundant ions originating from the cleavage between the 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) unit and the lipid A moiety are always present, giving important pieces of information about the structure of the molecules analyzed. Remarkably, in most cases, the comparison of the MALDI mass spectra of the intact R-type LPS with the O-deacylated one allowed us to obtain the structure of the lipid A moiety.