REVERSED-PHASE LIQUID-CHROMATOGRAPHY COUPLED ONLINE WITH CAPILLARY GAS-CHROMATOGRAPHY .2. USE OF A SOLVENT VAPOR EXIT TO INCREASE INTRODUCTION VOLUMES AND INTRODUCTION RATES INTO THE GAS-CHROMATOGRAPH

A large-volume introduction system for capillary gas chromatography (G C) is described which can be coupled on-line with reversed-phase liqui d chromatography (LC) using 2 mm i.d. LC columns. An on-column interfa ce with a special retention gap, coated with a very thin film (0.02 mu m) of Carbowax was used. Insertion of a solvent vapor exit before the analytical gas chromatography column allowed the solvent evaporation r ate for an azeotropic acetonitrile/water mixture (84:16, v/v) to incre ase from 20 to 175 muL min-1 at 91-degrees-C and 150 kPa inlet pressur e. A volume of 200 muL of this mixture containing phenanthrene and the potential basic drug eltoprazine, could be injected into the retentio n gap at introduction rates of up to 200 muL min-1, under partially co ncurrent solvent evaporation conditions. Repeatability (CV = 2.4%) and linearity (at least 10-1000 ng mL-1) were satisfactory. The Carbowax- coated retention gap has a relatively large retention power for the po lar solute. This means that the solvent can be completely evaporated t hrough the vapor exit without loss of analyte. With apolar solutes, lo sses will occur if evaporation is unduly prolonged. In order to allow the use of a nitrogen-phosphorus detector, a special pressure-balanced carrier gas circuit was designed and tested for total solvent-free pe rformance of the detector. With this set-up, 150 muL injections of elt oprazine in the acetonitrile/water azeotrope were made at an introduct ion rate of 200 muL min-1. No traces of acetonitrile were detected, wh ile analyte detectability was 20-fold higher than with the FID. Finall y, the practicability of reversed-phase LC-GC was demonstrated by on-l ine heart-cutting of the phenanthrene-containing fraction from a 2 mm i.d. LC column using acetonitrile/water (84:16, v/v) as eluent, and an alyzing it by capillary GC-FID.