Does oral fluid contribute to exhaled breath samples collected by means of an electret membrane?

To date, blood (and serum) as well as urine samples are the most commonly collected specimens for routine doping controls, which allow for the analytical coverage of an extensive set of target analytes relevant to sports drug testing programs. In the course of studies to identify potential alternative matrices to complement current testing approaches, exhaled breath (EB) has been found to offer advantageous properties especially with regard to the sample collection procedure, which is less invasive, less intrusive, and less time-consuming when compared to conventional blood and urine testing. A yet unaddressed question has been the potential contribution of oral fluid (OF) to EB samples. The current investigation focused on characterizing an electret membrane-based EB collection device concerning a potential introduction of OF during the sampling procedure. For that purpose, EB and OF samples collected under varying conditions from a total of 14 healthy volunteers were tested for the presence of abundant salivary proteins using bottom-up proteomics approaches such as SDS-PAGE followed by tryptic digestion and chromatographic-mass spectrometric analysis. The trapping baffles integrated into the mouthpiece of the EB collection device were found to effectively retain OF introduced into the unit during sample collection as no saliva breakthrough was detectable using the established analytical approach targeting predominantly the highly abundant salivary α-amylase. Since α-amylase was found unaffected by storage, smoking, food intake, and exercise, it appears to be a useful marker to reveal possible OF contaminations of EB collection devices.