Study of Matrix Additives for Sensitive Analysis of Lipid A by Matrix-Assisted Laser Desorption Ionization Mass Spectrometry

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been widely used for structural characterization of bacterial endotoxins (lipid A). However, the mass spectrometric behavior of the lipid A molecule is highly dependent on the matrix. Furthermore, this dependence is strongly linked to phosphorylation patterns. Using lipid A from Escherichia coli O116 as a model system, we have investigated the effects of different matrices and comatrix compounds on the analysis of lipid A. In this paper, we report a highly sensitive matrix system for lipid A analysis, which consists of 5-chloro-2-mercaptobenzo-thiazole matrix and EDTA ammonium salt comatrix. This matrix system enhances the sensitivity of the analysis of diphosphorylated lipid A species by more than 100-fold and in addition provides tolerance to high concentrations of sodium dodecyl sulfate (SDS) and tolerance to sodium chloride and calcium chloride at 10 mu M, 100 mu M, and 10 mu M concentrations. The method was further evaluated for analysis of lipid A species with different phosphorylation patterns and from different bacteria, including Helicobacter pylori, Salmonella enterica serovar Riogrande, and Francisella novicida.