High resolution mass spectrometry exhalome profiling with a modified direct analysis in real time ion source

Rationale Exhaled breath contains many substances that are closely related to human metabolism. Analysis of its composition is important for human health, but it is difficult. Since the volatile molecules in breath samples are exhaled instantaneously, easily diffused and modified, and at low level of presence, difficult to identify and quantify. Methods A modified direct analysis in real time (DART) ion source was used for high resolution mass spectrometry measurement of human metabolites in exhaled breath through online monitoring and offline analysis, in both positive and negative ion modes. The improved system enabled the breath volatiles as well as condensates to be directly sampled, rapidly transmitted and efficiently ionized in a confined region, and then detected by Orbitrap mass analyzer. Results The molecular features with online and offline analysis of exhaled breath were demonstrated with obvious differences. A total of  65 metabolites in positive ion mode and  55 metabolites in negative ion mode were identified based on accurate m/z values. Exhalome profile and the composition proportion of different classes of compounds were obtained. The relative contents of metabolites from breath varied during different time periods throughout a day. Conclusions A more complete picture of the human breath metabolome was provided combining the results obtained from both online and offline analysis. The developed method is capable of analyzing breath samples with different status rapidly and directly, and it is featured by simple operation, and metabolite identification, requiring little or no sample preparation.