A Comparison of Ethanolamine and Potassium Hydroxide as Quantitative Trapping Agents for Radiolabeled CO2 in Metabolism Studies

The efficiency of ethanolamine and potassium hydroxide (KOH) as trapping agents for CO2 was determined using a flow of 500 mL/min through CO2 absorption towers containing trapping solutions. Radiolabeled 14CO2 was produced by acidification of suspensions containing Ba14CO3. Both 100% ethanolamine and 5M ethanolamine in 2-methoxyethanol were evaluated. With 200 mL of either solution, trapping efficiency of 14CO2 decreased when only 5% or less of the amount of ethanolamine available had reacted (22 mmoles of CO2 trapped). In contrast, use of 200 mL of 1M or 5M KOH was effective in retaining 88 mmoles of CO2. This is equivalent to the amount of CO2 produced by a rat over an 8-hr period. In summary, with flow rates commonly used in in vivo metabolism studies, the trapping efficiency of ethanolamine was far less than the theoretical efficiency. In these types of studies KOH would be a more suitable trapping agent or, if used, ethanolamine solutions must be changed frequently.