title: Real-Time Quantification of Amino Acids in the Exhalome by Secondary Electrospray Ionization-Mass Spectrometry: A Proof-of-Principle Study.
abstract: Amino acids are frequently determined in clinical chemistry. However, current analysis methods are time-consuming, invasive, and suffer from artifacts during sampling, sample handling, and sample preparation. We hypothesized in this proof-of-principle study that plasma concentrations of amino acids can be estimated by measuring their concentrations in exhaled breath. A novel breath analysis technique described here allows such measurements to be carried out in real-time and noninvasively, which should facilitate efficient diagnostics and give insights into human physiology.
  
  
  
  The amino acid profiles in 37 individuals were determined by ion-exchange HPLC in blood plasma and simultaneously in breath by secondary electrospray ionization coupled to high-resolution mass spectrometry. Participants were split into training and test sets to validate the analytical accuracy. Longitudinal profiles in 3 individuals were additionally obtained over a 12-h period.
  
  
  
  Concentrations of 8 slightly volatile amino acids (A, V, I, G, P, K, F, Orn) could be determined in exhaled breath with a CV of <10%. Exhalome validation studies yielded high accuracies for each of these amino acids, on average only 3% less compared to plasma concentrations (95% CI ±13%). Higher variations were found only for amino acids with a low plasma concentration.
  
  
  
  This study demonstrates for the first time that amino acids can be quantified in the human breath and that their concentrations correlate with plasma concentrations. Although this noninvasive technique needs further investigation, exhalome analysis may provide significant benefits over traditional, offline analytical methods.
authors.affiliation: Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich, Switzerland;
authors.forename: Diego
authors.initials: D
authors.lastname: García-Gómez
authors.affiliation: Department of Pulmonology, University Hospital Zurich, Zurich, Switzerland; Hospital Zollikerberg, Zollikerberg, Switzerland;
authors.forename: Thomas
authors.initials: T
authors.lastname: Gaisl
authors.affiliation: Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich, Switzerland;
authors.forename: Lukas
authors.initials: L
authors.lastname: Bregy
authors.affiliation: Division of Clinical Chemistry and Biochemistry, University Children's Hospital Zurich, Zurich, Switzerland;
authors.forename: Alessio
authors.initials: A
authors.lastname: Cremonesi
authors.affiliation: Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich, Switzerland;
authors.forename: Pablo Martinez-Lozano
authors.initials: PM
authors.lastname: Sinues
authors.affiliation: Department of Pulmonology, University Hospital Zurich, Zurich, Switzerland; Centre for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
authors.forename: Malcolm
authors.initials: M
authors.lastname: Kohler
authors.affiliation: Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, Zurich, Switzerland; zenobi@org.chem.ethz.ch.
authors.forename: Renato
authors.initials: R
authors.lastname: Zenobi
mesh_terms: D000596:Amino Acids / Q000032:analysis*; D001944:Breath Tests; D002851:Chromatography, High Pressure Liquid; D045853:Exhalation; D006801:Humans; D021241:Spectrometry, Mass, Electrospray Ionization; D013997:Time Factors
chemical_list: D000596:Amino Acids