Low cost, robust, in-house hardware for heart cutting two-dimensional gas chromatography

Abstract

Natural materials are so complex that no single column can separate all of the components. Heart cutting 2-D GC (GC-GC) using a Deans switch provides maximum separation, but the requisite gas flow configurations have earned a reputation for being fiddly and time consuming to set up and tune, unless electronic gas controls and costly software are employed. A design for a vented Deans switch is presented that can be assembled in-house from standard commercial components. A vent to atmosphere replaces the balancing resistor, which solves the problem of balancing the pressures and flows, and requires no compensation for changes in gas viscosity and back-pressure during temperature programming. First and second dimension columns can both be run at optimum flow rates, even if they are of different diameters. Analyte detectability is preserved by cutting only the target fraction from the first column and transferring the whole of it to the second column. Cryotrapping the selected fraction allows cuts of any width and transfer of analytes to the second column as sharp bands. The author has applied the vented Deans switch–cold trap to the identification of flavour and fragrance compounds from South African plants and foods; cuts are very repeatable, and the detectability of trace components is enhanced. Its capabilities are demonstrated by examples from analyses of essential oils and flavour extracts.