Electron-capture detection in reversed-phase liquid chromatography using packed-capillary columns

A new type of interface has been developed for the direct coupling of packed-capillary reversed-phase liquid chromatography with electron-capture detection. This interface allows the detection of relatively non-volatile and/or polar compounds, and simply consists of a fused-silica capillary (50 μm I.D.) inside of a stainless-steel capillary (0.32 mm I.D.) connecting the analytical column with the detector through the oven wall. The make-up gas is used for cooling of the fused-silica capillary. With flow-injection analysis the influence of several parameters (e.g. flow-rate of the make-up gas and mobile phase, oven temperature) on the performance of the total system (i.e. band broadening, sensitivity) has been studied. Using optimal conditions (flow-rate 2 μl min−1, make-up gas 40 ml N2 min−1, oven temperature 300 °C, injection volume 60 nl) separation and detection of mononitroanilines, chlorophenols, pesticides and benzodiazepines have been performed. Detection limits are in the range of 10–450 pg (0.2–7 mg 1−1) under reversed-phase conditions. Large-volume injections up to 15 μl, using a non-eluting solvent (water) to focus the analytes on top of the column, have been performed to increase the sensitivity of the system. This technique increased the concentration sensitivity with 2–3 orders of magnitude allowing the detection of ca. 150 ng 1−1 of chlorophenols in river Meuse water.