A method for determination of carbon dioxide specific radioactivity and concentration in blood, rumen fluid, and expired air

A method is described for determining specific radioactivity and concentration of CO₂ in blood, rumen fluid, and expired air. The CO₂ of blood and rumen fluid samples is liberated selectively by 1 m phosphate buffer (pH 5.8) containing 1 mm NaN₃ and 5 mm NaF. Liberated CO₂ is quantitatively trapped in 0.3 n Ba(OH)₂, and amounts of CO₂ are determined by titration of residual hydroxide ion. The resulting BaCO₃ is solubilized with 10% EDTA in 1 m Tris (pH 9), and radioactivity is determined by liquid scintillation. For quantitative determination of expired CO₂, a measured fraction of expired air is bubbled through 0.3 n Ba(OH)₂. The amount of trapped CO₂ is determined by titrating residual hydroxide ion in an aliquot of trapping solution after BaCO₃ is precipitated by centrifugation. Radioactivity is determined by liquid scintillation spectrophotometry of ethanolamine carbamate after CO₂ is regenerated from BaCO₃ by addition of acid and quantitatively retrapped in ethanolamine.