Figure 1

Experimental approach of IR-IS, combining mass spectrometry with infrared spectroscopy for metabolite identification. In panels (a–c), grey spectra are full +ESI MS spectra of body fluid samples and black spectra are generated after isolation of ions at m/z 244. Panel (a) shows the MS spectrum of a control CSF sample demonstrating the absence of ions corresponding to the m/z value expected for ManNAc ([M + Na]⁺ m/z 244), the targeted biomarker in these experiments. Panels (b) and (c) contain MS spectra generated from (b) a CSF sample and (c) a urine sample from a patient having NANS deficiency. Panel (d) illustrates the mass isolation of ions at m/z 244, and the subsequent measurement of their IR spectrum in the ion trap (black trace). In panel (e), the route to identification is achieved via IR spectral match between the spectrum measured from the patient sample (black in all graphs) and reference spectra generated for the known model compounds of alternative N-acetylhexosamines. The IR spectra serve as structural signatures, in this case providing clear identification of the species at m/z 244 from the patient sample as ManNAc by spectral match with the reference IR spectrum (red).