Analysis of a stable halogenated derivative of muramic acid by gas chromatography–negative ion chemical ionization tandem mass spectrometry

Muramic acid (Mur) is present in the cell wall of Eubacteria and serves as a chemical marker for the trace detection of bacteria and bacterial cell wall debris in complex matrices. There have been numerous studies using a variety of derivatives of Mur, particularly in combination with gas chromatography–tandem mass spectrometry (GC–MS–MS) where the detection limit has been steadily lowered. A stable, halogenated derivative, the pentafluorobenzyl oxime (PFBO) acetate of Mur, has been developed by others and successfully used for GC with electron-capture detection. The current report is the first use of this derivative for GC–MS–MS analysis of Mur, or indeed any other carbohydrate, using negative ion chemical ionization (NICI) with GC–MS–MS. Mur was readily detected in settled surface dust (166 ng/mg), as well as dust collected from indoor air (1.4–5.9 ng/mg). Analyses of Mur as a PFBO acetate by GC–NICI-MS–MS or as alditol acetates by electron impact GC–electron impact ionization MS–MS serve as complementary approaches for trace detection in complex matrices.