The field of breathomics has been around for centuries, dating back to ancient times when philosophers and scientists realized “sweet odor” in human breath was a sign of illness. They may not have had a name for diabetes back then, but they were able to recognize it. The analysis of breath for disease biomarkers has continued since then, although it’s not quite as popular as its potential suggests.
Chinese researchers recently placed a solid-phase microextraction (SPME) fiber in the N95 face masks of volunteers to test the fiber’s in vivo sampling and collection capabilities. The SPME fiber was then coupled with direct analysis in real-time mass spectrometry (DART-MS) to analyze the composition of aerosols in exhaled breath. The results, recently published in Analytical Chemistry, show the method can successfully analyze both volatile and non-volatile analytes in breath, and the researchers say they “expect it to have a significant impact on human [exhaled breath aerosol] analysis in clinical applications.”
Mass spectrometry has always been the method of choice for breath analysis due to its sensitivity, but sample collection is tricky. For MS to work correctly, sufficient amounts of breath molecules must be collected, which often requires tedious procedures such as breathing into a tube or bag. With most of the world wearing face masks due to COVID-19, Bin Hu and colleagues wondered if they could find a way to use those face masks to better collect aerosols exhaled in breath.
For the study, volunteers wore standard N95 masks with a SPME fiber for two hours after chewing gum, eating a banana, eating garlic and smoking. When the researchers removed the fiber and directly coupled it with DART-MS, they detected specific compounds—even at trace levels—associated with each activity. For example, volatile compounds such as a cooling agent and butyl butyrate were identified in the fibers of volunteers who chewed gum and ate a banana, respectively. The method also successfully detected non-volatile analytes, with the mass spectrum clearly showing caffeine two hours after a participant drank a cup of coffee.
“More nonvolatile analytes, e.g., salbutamol and metronidazole, were detected in EBA [exhaled breath aerosol] after an asthma aerosol drug and mouthwash were sprayed into the oral cavity of healthy volunteers. These data clearly show that analytes, whatever volatile and nonvolatile compounds, in oral EBA can be sampled by SPME-in-mask and analyzed by DART-MS,” the researchers write in their paper.
SPME-in-mask sampling boasts two additional unique advantages: it is selectable, and it eliminates the possibility of chemical contamination. According to the researchers, the extraction fibers of SPME are selectable to target analytes. For example, they found PDMS/DVB-SPME fibers provide enhanced sensitivity and sensitivity when extracting volatile polar analytes, such as nicotine and cotinine, while PDMS-SPME fibers are better suited for the analysis of low polar analytes, such as xylometazoline (decongestant) and budesonide (corticosteroid). Considering face masks are intended to protect users from external contamination—be it pollution or SARS-CoV-2—the study participants were able to avoid all contamination during the SPME sampling process. Given typical study parameters, this is extremely rare but highly desirable, especially for clinical applications that require in vivo sample and analysis.
Due to the commonality of SPME fibers and face masks, the researchers say SPME-in-mask sampling is suitable for additional analysis, including LC, GC, LCMS, GCMS and other MS-based methods. Overall, though, the researchers hope their new DART-MS method is used to screen for disease biomarkers on a large scale.
“We also hope this method will inspire biomarker screening of some epidemic respiratory diseases that were usually required to wear a face mask in daily life,” they conclude.
Photo: Schematic diagram of SPME-in-mask, a) SPME fiber inserted into face mask (KN95), b) SPME-in-mask was wearing for collecting EBA, c) direct coupling of SPME with DART-MS. Credit: Yuan, Z.C. Solid-Phase Microextraction Fiber in Face Mask for In Vivo Sampling and Direct Mass Spectrometry Analysis of Exhaled Breath Aerosol. Anal. Chem. 2020 Jul 28.