|Pseudomonas aeruginosa (PA) infections in the cystic fibrosis (CF) lung are the primary cause of morbidity and mortality for the 30,000 Americans afflicted with CF. Once acquired from environmental reservoirs, PA mutates in the CF lung, leading to a decrease in lung function. Presently, these mutations cannot be detected in situ. We aim to identify volatiles that are associated with PA mutation in the CF lung using GCxGC-TOF, and develop methods for the rapid detection of volatile biomarkers by SESI-MS. These results will be transferable to the CF clinic where PA infections can be diagnosed rapidly via SESI-MS breath analysis.