Carbon dioxide flush, measuring

The supercritical fluid flushes the extraction cells with a volume of 10 ml and is then expanded in the restrictors. In order to prevent the drive out of solid particles, there are frits with 5 pm pore size at the ends of the extraction cell. With fluid expansion, extracted particles precipitate and are kept in the vials which contain an organic solvent for sampling. Measured average carbon dioxide currents at the end of the extractor were 12 liters at a temperature of 28 °C and 1 bar pressure, resulting in a current of 0.81 ml/min carbon dioxide at the above-metioned extraction conditions. 

In the alternative, open-circuit type of chamber (Hg. 11.4b), air is drawn through the chamber at a metered rate and sampled for analysis on entry and exit.Thus, carbon dioxide production, methane production and oxygen consumption can be estimated. As the differences in composition between inlet and outlet air must be kept small if conditions for the animal are to be kept normal, very accurate measures of gas flow and composition are required. Modern equipment, based on infrared analysers, meet this criterion, and open-circuit chambers have now largely replaced closed-circuit chambers.AMth some chambers it is possible to alternate between closed- and open-circuit operation. Closed-circuit operation for perhaps 30 minutes, with no gas absorption, produces appreciable changes in the composition of the chamber air. Then a brief period (about 3 minutes) of open-circuit operation allows the chamber air to be flushed out through a flow meter and sampling device. 

---