THE EFFECTS OF INLET LINER CONFIGURATION AND SEPTUM PURGE FLOW-RATE ON DISCRIMINATION IN SPLITLESS INJECTION

An unmodified split/splitless inlet system using forward-pressure cont rolled pneumatics was operated in splitless injection mode with severa l inlet liners under a range of septum purge flow rates. The relative recovery (discrimination) of hydrocarbons ranging from n-C-8 to n-C20 depended strongly upon the injected sample volume with open-ended line rs at high septum purge flow rates of e.g. 50 mL/min. Little or no dis crimination was observed at septum purge flows of 2-3 mL/min.The same inlet was also operated in a back-pressure regulated configuration tha t produced mass discrimination similar to that observed with the highe r septum purge flows in the forward-pressure configuration. An inlet l iner with a restricted inlet and outlet gave mass-discrimination level s independent of septum purge flow rate, but in the reverse sense of t hat observed with open-ended liners. Preferential volatile-component l osses out of the inlet liner to the septum purge vent are principally responsible for the observed mass discrimination with open-ended liner s, while mass-dependent losses with doubly-restricted liners seem due to slow sample evaporation.