Monitoring muramic acid in air (after alditol acetate derivatization) using a gas chromatograph-ion trap tandem mass spectrometer

Abstract Muramic acid is a chemical marker for bacterial peptidoglycan. Air monitoring was performed in a stable and a dairy. Airborne dust was collected for 68–95 h on Teflon filters for muramic acid analysis. Filters were cut in two and the replicates analyzed separately. The filters and associated dust were heated in sulfuric acid to release muramic acid. Muramic acid was converted to muramicitol pentaacetate lactam and analyzed by gas chromatography-tandem mass spectrometry using a non-polar GC column (DB-5MS). An ion trap tandem mass spectrometer was used for detection. The precursor mass spectrum of muramic acid was dominated by one major high mass ion m z 403 (loss of ketene, m z 42, from the molecule, MW 445) and m z 198 was the most abundant ion in daughter spectra. Both ions retained the unique lactam ring structure. Using multiple reaction monitoring (MRM), the transition m z 403 to m z 198 was used in quantitation. 13 C-labeled muramic acid was used as an internal standard (monitoring the corresponding ion transition m z 412 to m z 205). MRM chromatograms were free of extraneous background peaks. Excellent sensitivity was also observed with daughter spectra for m z 403 allowing absolute identification of muramic acid in airborne dust.