Separation of radiolabeled CO2 from volatile parent compound(s) or degradation products in air from biodegradation microcosms has been done by using solubility in alkaline vs. nonpolar solvents or solutions. However, trapping solvents or solutions used to collect radiolabeled CO2 may absorb some volatile intermediate products or the volatilized parent compound. Similarly, solvents used to trap volatile radiolabeled degradation intermediates or volatile parent compound may absorb some radiolabeled CO2. If this lack of absorption specificity is significant, the clear interpretation of radioactivity-counting analyses may be compromised.
A procedure designed to separate volatilized [7-14C]naphthalene and 14CO2 from the same air stream was evaluated for its efficiency. Ethylene glycol monomethyl ether (EGME) effectively trapped naphthalene (98.6% recovery) but retained approximately 0.8% of the 14CO2, whereas monoethanolamine (MEA):methanol:scintillation cocktail solution trapped approximately 99.5% of the naphthalene and virtually 100% of the CO2. Preliminary studies of the efficiency of trapping solutions for parent compounds and mineralized CO2 should be made before conclusions are made concerning the extent or rate of mineralization based on the amount of radiolabeled carbon retained in a trapping solution.