Collecting exhaled breath condensate(EBC) with two condensers in series: a promising technique for studying the mechanisms of EBC formation, and the volatility of selected biomarkers

Exhaled breath condensate (EBC) consists mainly of water, but also contains semivolatile and nonvolatile compounds. The aim of this study was to develop a system in which two. condensers are simultaneously used in series to clarify the mechanisms of EBC condensation. Two aliquots of EBC (EBC1 and EBC2) were collected from 20 asymptornatic smokers and 20 healthy young nonsmokers using a specifically designed device having two condensers in series in which total volume, hydrogen peroxide (H2O2), ammonium (NH4+), and conductivi, ty before and after lyophilization were measured. Water, NH4+ levels and conductivity before lyophilization were significantly lower in the EBC2 than in the EBC1 of smokers and nonsmokers; the contrary was true for H2O2 levels. Almost all nonvolatile salts were collected in the first condenser, because more than 50% of postlyophilization conductivity was below the detection limit in EBC2. The recovery of volatile molecules and their derivatives (water and NH4+) was partial in the first condenser, but appreciable amounts of both were measured in the second; however, the condenser immediatelyin contact with exhaled air was more effi-, cient in terms of water, NH4+ and conductivity before lyophilization. On the contrary, nonvolatile ions (conductivity after lyophilization) were mainly collected in the first condenser. Finally, the behavior of H2O2 cannot be explained on the basis of its chemical and physical properties, and the most probable explanation is that some was byproduced by a radical reaction in the gas phase or during the condensation process in water.