On‐line combination of liquid chromatography and capillary gas chromatography. Preconcentration and analysis of organic compounds in aqueous samples

Abstract

This paper describes the design of a new, versatile, and low‐cost on‐line LC‐GC interface that allows the fast and reliable introduction of large sample volumes onto a capillary GC column. The sample introduction procedure consists successively of: evaporation of the entire sample (LC fraction), selective removal of the solvent and simultaneously cold‐trapping of the solutes, splitless transfer of the solutes to the GC column, on‐column focusing, GC separation and detection. Quantitative and qualitative aspects of various experimental parameters are evaluated and optimum conditions are reported. The applicability of the method is demonstrated on a synthetic aqueous sample of chlorinated pesticides.

Coupled High Performance Liquid Chromatography with High Resolution Gas Chromatography

“…An early vapour exit is usually placed after a few metres of the deactivated precolumn (9) and a short piece (3 -4 m) of the main column (retaining precolumn). This valve is opened during solvent evaporation in order to reduce the amount of solvent that would reach the detector, and at the same time, to increase the solvent evaporation rate (6).…”

“…This technique allows the use of shorter retention gaps or larger transfer volumes. In theory, an early vapour exit (6) should be placed between the uncoated precolumn and the main column, but in practice a short section of the main column (7) is placed between the precolumn and the vapor exit, so rendering the closure of the vent less critical.…”

Other Modes of Detection

“…The reduction may be done by stream splitting [269,270], which reduces sensitivity, LC miniaturization [277,278], or solvent evaporation using a retention gap to avoid band broadening [265,267,279,280]. The peak of interest must first be found; the solvent volume is then reduced and an injection is made into the GC.…”

LC/GC, SFC/GC, and SFE/GC

“…Successful applications have avoided transferring large volumes of aqueous eluent into the gas chromatograph. Instead these applications use either the autoinjection interface (32) or pure acetonitrile eluent with an RG and gastransfer interface (20) or a solvent-exchange interface (33,34).…”