[en] Method and apparatus for the processing of fluid materials, particularly in the preparation of samples for radioactive isotope tracer studies by combustion of starting materials containing such isotope tracers. The sample is burned in a combustion chamber which tapers upwardly and inwardly above the sample receptacle so as to approximate the shape of the flame of a burning sample, and the combustion products are continuously exhausted from the combustion chamber and passed through a heat exchanger which condenses the condensable vapors in the combustion products. The condensed vapors are then separated from the gases, and the gases are passed into a reaction column if there is a radioactive isotope tracer remaining in gas form. Oxygen is fed into the combustion chamber at a controlled rate during combustion, and after combustion nitrogen gas is fed into the combustion chamber and exhausted therefrom through the heat exchanger and into the separating means, so as to purge the system of any remaining gaseous production products. A liquid scintillator, and a liquid solvent if desired, are passed through the heat exchanger into the separating means after each combustion so as to recover any residual condensed vapors. In the reaction column, the gas containing the radioactive isotope tracer is reacted with a trapping agent in a column comprising a series of smoothly contoured reaction chambers interconnected by smoothly contoured necked down portions. After all the gases have been passed through the column, the direction of gas flow is reversed in the column so as to discharge the reaction product into a counting vial. A liquid scintillator, and a liquid solvent if desired, are then passed through the reaction column following the same procedure as followed previously for the trapping agent, thereby recovering all the reaction product from the column