Investigation of Organic Vapor Losses to Condensed Water Vapor in Tedlar^® Bags Used for Exhaled-Breath Sampling

This study evaluated the potential loss of organic vapors to condensed water in bags used for breath sampling. "Wet" test atmospheres were prepared by transferring nitrogen into 1-L Tedlar^® bags and spiking with water and each of several organic solvents (methanol, acetone, 2-butanone,m-xylene, 1,1,1 trichloroethane, and perchloroethylene) to yield atmospheres representative of a 500-mL breath sample collected at 37°C and cooled to 25°C. Vapor concentrations were compared with those in bags prepared without water. Differences between mean concentrations in wet and dry bags were significant only for methanol, which yielded a mean wet-bag concentration approximately 10% lower than for dry bags. In a second series of experiments the same initial concentration of solvent vapor was generated in 1 dry bag and 5 bags containing 1 to 20 times the amount of water expected to condense in a 500-mL breath sample. Significant differences between wet and dry bag concentrations were seen for methanol, acetone, and 2-butanone; however, the quantity of water reguired to produce this difference in the acetone and 2-butanone bags exceeded three times that expected to condense in a breath sample. Results were in good agreement with predictions based on Henry's law. In both experiments permeation of water vapor out of the bags led to a decrease in the quantity of condensed water, thereby reducing the extent of organic vapor partitioning. These results indicate that solvent vapor loss to condensed water is not likely to be significant under typical conditions.