14CO2 Measurement in Air:  Literature Review and a New Sensitive Method

A simple method has been developed for the measurement of low concentrations of 14CO2 in air. CO2 and 14CO2 are quantitatively absorbed by 2-methoxypropylamine in a newly developed intensive wash bottle with reflux cooling after intensive drying with silica gel and phosphorus pentoxide. The maximum air flow rate is 3.5 L min-1, which is relatively high as compared to the volume of absorbent (50 mL). A maximum of 10 m3 air can be sampled within a sampling period of 48 h. Aliquots of 10 mL of absorbent, corresponding to 2 m3 CO2 equivalent of air or about 0.4 g of CO2 carbon, can be measured in one sample by liquid scintillation counting. The sampling efficiency is better than 99.98%, and the detection limit is lower than the ambient 14CO2 background of 54 mBq m-3. The remarkable features of the new method are as follows: low limit of detection, easy sample preparation, and the possibility of short-term measurements. The new air sampler is currently used in wind-tunnel experiments, where 14CO2 is largely diluted, in order to quantify the mineralization of 14C-labeled environmental chemicals in agroecosystems.