Splitless Injection with Solvent Trapping

If solvent is injected by vaporizing injection into a column maintained at a temperature below the solvent boiling point, the vapour leaving the injector will, under certain conditions, condense in the column inlet. Splitless injection incorporating solvent trapping exploits this behaviour. The injector used is similar in design to some splitters (Figure 1), in that it has outlets to the column and splitter and a septum purge. During injection and for a short time afterwards (so-called 'splitless period') the injector and (often) septum purge vents are kept closed and the only exit from the injector is onto the column. At other times the vents remain open.

The injector vent is for rapid removal from the injector of material not reaching the column during

Figure 1 The split - splitless injector.

the splitless period. The vent flow is set to 20-100mLmin~1. The purpose of the septum purge (1-2 mL min"1) is as described above.

For injection, the oven temperature is set to <20°C below the solvent boiling point (the optimum temperature is best determined experimentally), the vents are closed and the sample (1-2.5 |L) injected. After the splitless period (20-60 s) the vents are opened and chromatography initiated. The condensed solvent in the column acts as a thick layer of stationary phase, which dissolves the sample's components. Carrier gas passing over the film is rapidly saturated with solvent vapour so all solvent evaporation occurs at the rear of the film. As the length of the solvent film decreases, sample components remain in solution in the narrowing band of liquid. When the last trace of solvent evaporates, the sample components will have been concentrated into a narrow band from which to start chromatography.

Exploitation of solvent trapping is not limited to injection of liquids. If 2-3 | L solvent is condensed in the column inlet it can be used to trap volatile organic compounds injected as a vapour immediately afterwards (i.e. before the solvent has evaporated). This could be useful for headspace analysis.

Solar Panel Basics

Solar Panel Basics

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