DEVELOPMENT OF A DUAL CAPILLARY COLUMN GC METHOD FOR THE TRACE DETERMINATION OF C2-C9 HYDROCARBONS IN AMBIENT AIR

An analytical method based on a dual capillary gas chromatographic tec hnique combining the advantages of GasPro PLOT and a non polar narrow bore WCOT column was developed for the analysis of air samples contain ing C2-C9 NMHCs. A refocusing step was not required due to the fast he ating rate of the sample preconcentration trap and the resolving power of the PLOT column for C2 and C3 NMHCs. Water had to be removed from the air samples to avoid plugging of the columns if the initial GC ove n temperature was below ambient temperature. To dry air samples, a scr ubber and a cryogenic technique were employed. The interferences cause d by carbon dioxide were reduced by purging the loaded sample preconce ntration trap with helium. The dual column system was compared to a me thod employing a refocusing device and a single narrow bore WCOT colum n. Both systems provided a high degree of precision. However, the dual column approach was superior to the single column system due to bette r resolution of low molecular weight components.