Reversed‐phase liquid chromatography coupled on‐line with capillary gas chromatography II. Use of a solvent vapor exit to increase introduction volumes and introduction rates into the gas chromatograph

Abstract

Abstract. A large-volume introduction system for capillary gas chromatography (GC) is described which can be coupled on-line with reversed-phase liquid chromatography (LC) using 2 mm i.d. LC columns. An on-column interface with a special retention gap, coated with a very thin film (0.02 pm) of Carbowax was used. Insertion of a solvent vapor exit before the analytical gas chromatography column allowed the solvent evaporation rate for an azeotropic acetonitrilelwater mixture (84: 16, vlv) to increase from 20 to 175 pL mh-' at 91°C and 150 kPa inlet pressure. A volume of 200 pL of this mixture containing phenanthrene and the potential basic drug eltoprazine, could be injected into the retention gap at introduction rates of up to 200 pL min-', under partially concurrent solvent eva oration conditions. Repeatability (CV = 2.4%) and linearity (at least 10-1000 ng mL-) were satisfactory. The Carbowax-coated retention gap has a relatively large retention power for the polar solute. This means that the solvent can be completely evaporated through the vapor exit without loss of analyte. With apolar solutes, losses 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 performance of the detector. With this set-up, 150 pL injections of eltoprazine in the acetonitrile/water azeotrope were made at an introduction rate of 200 pL min-'. No traces of acetonitrile were detected, while analyte detectability was 20-fold higher than with the FID.Finally, the practicability of reversed-phase LC-GC was demonstrated by on-line heart-cutting of the phenanthrene-containing fraction from a 2 nun i.d. LC column using acetonitrile/water (84: 16, v/v) as eluent, and analyzing it by capillary GC-FID.

Rapid and Simultaneous Analysis of Free Sterols, Tocopherols, and Squalene in Edible Oils by Coupled Reversed-Phase Liquid Chromatography−Gas Chromatography

“…Different aspects concerning the design of robust and reliable interfaces that enable direct transfer of aqueous eluents have been previously investigated (Goosens et al, 1994;Mol et al, 1993;Staniewski et al, 1992 et al, 1991). Specifically, our previous research in RPLC-GC coupling using a programmed temperature vaporizer (PTV) as interface of the system has shown its usefulness for the direct analysis of minor components, for example, free sterols of edible oils (Sen ˜ora ´ns et al, 1996).…”

On-line sample treatment—capillary gas chromatography

“…Goosens et al used a Carbowax-deactivated retention gap to transfer acetonitrile-water eluents from the LC to the GC part of the system [147][148][149]. Up to 200 pL of eluent were introduced into a Carbowax-coated retention gap using an on-column interface and solvent vapour exit [148]. It was found that the water content of the eluent should indeed not exceed that of the azeotropic mixture, otherwise water which is left in the gap after evaporation of the azeotropic mixture will mar the analysis.…”

“…Obviously the OV-1701-treated retention gap is a valid answer to the problem of (accidental) introduction of traces of water, but does not allow the introduction of substantial amounts of water. Goosens et al used a Carbowax-deactivated retention gap to transfer acetonitrile-water eluents from the LC to the GC part of the system [147][148][149]. Up to 200 pL of eluent were introduced into a Carbowax-coated retention gap using an on-column interface and solvent vapour exit [148].…”

HighlightMultidimensional Approaches in Environmental Analysis

“…Water-resistant retention gaps have been produced, injection volumes have been made very small and LC eluent composition has been optimized [with some success, as 200 ml of the azeotropic mixture acetonitrile-water (84 + 16, v/v) could be introduced]. 8 Rather different alternatives have also been studied. One involves the on-line liquid-liquid extraction (LLE) of the LC eluent fraction of interest with a suitable organic solvent with subsequent phase separation and on-line transfer of the organic extract to the GC part of the system.…”