Investigations on analyte losses in systems suited for large-volume on-column injections

Use of a large-volume injection system with a solvent vapour exit (SVE) req uires optimisation. An appropriate strategy is to determine the evaporation rate by increasing the injection time at a fixed infection speed, injectio n temperature and head pressure. When measuring the flow rate in the carrie r gas supply line to the on-column injector, optimisation can be very rapid : some five injections of pure solvent will be sufficient. When working under partially concurrent solvent evaporation conditions, los s of volatiles is often observed if no retaining precolumn is used between the retention gap and the SVE, To investigate the requirements (length and stationary phase) of the retaining precolumn, C8 - C18 n-alkanes in n-hexan e were used. The minimum length of the retaining precolumn (0.32 mm diamete r) needed to prevent substantial losses of volatiles was 2 m. Experiments w ith retaining precolumns with and without stationary phase gave identical r esults. This shows that there is no need to coat the capillary as it only a cts as a restrictor.