SIMPLE MEASUREMENT OF DEPOSITION VELOCITIES AND WALL REACTION PROBABILITIES IN DENUDER TUBES .2. HIGH DEPOSITION VELOCITIES

The methodology reported in Part I of this series is now extended and further developed to include measurements of relatively high depositio n velocities and reaction probabilities of gaseous analytes on a solid denuder wall coating. The method is based again on the reversed-flow gas chromatography technique, but employs a denuder tube coated only i n part of its total length with the solid. The mathematical formulatio n of the problem is similar to that of Part I, and is solved as before . It describes the diffusion band of each analyte in the form of a sum (or difference) of two exponential functions of time. The pre-exponen tial factors and the exponential coefficients of these functions are c omputed by a simple PC program of non-linear least-squares analysis. B y means of another two PC programs, the values of the diffusion coeffi cient of the analyte in the carrier gas, its deposition velocity on th e tube coated wall and the wall reaction probability are computed. The method has been applied to acetylene and sulphur dioxide in nitrogen, depositing on marble powder. Consistent results are obtained with the denuder tube coated alternatively on its upper or lower part, and the diffusion coefficients are in good agreement with those calculated th eoretically.