Trace Detection of Underivatized Muramic Acid in Environmental Dust Samples by Microcolumn Liquid Chromatography−Electrospray Tandem Mass Spectrometry

Muramic acid (MA) is a universal chemical marker for bacterial cell wall polymers (peptidoglycan) present in complex environmental, industrial, and clinical matrices. Trace analysis of MA has been limited to a handful of laboratories because of the lengthy nature of derivatization procedures necessary for GC/MS and GC/MS/MS. The focus of the current report concerns environmental analysis (organic dust) using LC/MS/MS of native MA. Dust was heated in sulfuric acid to release MA from cell wall polymers. Acid was removed by extraction with an organic base. The samples were passed through a hydrophobic C-18 extraction column to remove nonpolar contaminants. This was followed by binding of MA to a strong cation-exchange extraction column to eliminate neutral and anionic components of the sample. MA was then eluted with hydrochloric acid, which was removed by evaporation. Analysis was done by microscale LC ES/MS/MS using a custom-made Lichrosphere-diol capillary column. 13C-Labeled MA was used as an internal standard. Total sample preparation takes approximately 12 h. The simplicity of the sample preparation may eventually allow MA analysis to be used in a host of applications, including air monitoring for biocontamination. This is the first report, to our knowledge, of microscale LC ES/MS/MS analysis for MA (or, indeed, any other sugar monomer) in a complex matrix.