Programmed temperature vaporisation

Several sample preparation techniques are performed inside the inlet system. Large-volume injection can be carried out by a number of methods including programmed temperature vaporisation (PTV). Automated SPE may be interfaced to GC using a PTV injector for large volume injection. SPE-PTV-GC with on-column injection is suited to analysis of thermola-bile compounds. 

For routine analysis of liquid samples, four injection techniques are available split, splitless, on-column and programmed temperature vaporising injection [90]. 

Programmed temperature vaporisation Capillary Split Pulsed split Splitless Pulsed splitless Solvent vent High concentration High concentration Low concentration Low concentration Low concentration ... 

Some analytes are volatile enough to be analysed by GC, but too involatile to give sufficient sensitivity by headspace injection modes. In these cases, all may not be lost. The programmed temperature vaporiser (PTV) can provide a means of selectively injecting the desired analyte onto the column whilst excluding undesired components such as solvents and involatUes. This is variously known as selective extraction or selective exclusion. It permits large volume injections (LVI) and difficult matrix introduction (DMI). 

Engewald, W., J. Teske, and J. Efer. 1999. Programmed temperature vaporiser-based injection in capillary gas chromatography. J. Chromatogr. A 856 259-278. 

Brossa, L., Marce, R. M., Bormll, F., and Pocurull, E., Determination of endocrine-disrupting compounds in water samples by Online solid-phase extraction-programmed-temperature vaporisation-gas chromatography-mass spectrometry, J. Chromatogr A., 998, 41-50, 2003. 

Another approach has been to use a programmed-temperature vaporiser, which in essence is a split/splitless injector that is maintained at a temperature close to the boiling point of the injection solvent, so that the sample is transferred to the column In a liquid when the soivent has evaporated, the injector is heated at a rate of 14 C/sec to the minimum coiumn temperature required [383,384], The manufacturers (Perkin Eimer) ciaim that this injector is the ciosest to a universai system yet to be deveioped. 

Split injection is used for volatile to semi-volatile compounds, and is one of the easiest injection techniques. With this technique, the flow of carrier gas is split between the capillary column and the atmosphere. This split does not occur in case of splitless injection. Splitless injection is used in case residual solvents remain in the sample at low eon-centrations, due to increased sensitivity compared to split injection. Other possibilities of direct injection are on-column injection and Programmed Temperature Vaporisation (PTV) injection. Both techniques allow detection limits to achieve put levels but are large volxune injection techniques. In on-column injection systems, the sample is injected on a pre-colmnn and then the solvent is vented, leaving only the analytes to be injected on the coltunn. In PTV, after the sample injection, the solvent is evaporated at a low temperature in a packed chamber and then removed. This leaves the solutes on the packing. When the injection port is heated the analytes are transferred to the analytical column. ... 

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