Metabolomic signatures in nuclear magnetic resonance spectra of exhaled breath condensate identify asthma.

By using an Anacon condenser (Biostec, Valencia, Spain), different results have been reported [7]. Collection devices are an important source of variability of EBC biomarkers [2, 3, 8]. The principal variability factors include cooling temperature [9] and condenser materials [2]. For example, a warm-up during condensation is observed when RTube or Anacon are used (condensers using a disposable collection kit), whereas EcoScreen cools down slightly during the procedure [8, 9]. Such differences affect biomarker concentrations [2, 9]. More importantly, there was no correlation between biomarkers measured in EBC collected with EcoScreen and Anacon condensers [9], and there was only an ,60% correlation between biomarkers measured in EBC collected with RTube and Anacon condensers; although both used a disposable collection kit [9]. However, as no NMR details were found (i.e. the operating magnetic field, the number of acquisitions, the possible use of a cryoprobe, and the detection limit), it is difficult to conclude that NMR spectroscopy cannot be used to analyse EBC samples because it does not have the sensitivity required to observe the endogenous metabolites in the EBC [7]. With our spectrometer set-up, we have estimated a detection limit that is notably low for NMR-based metabolomics [10].