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This PTV injector is considered to be the most universal. It can be used successively as a cold on‐column injector and then as a split/splitless injector. The temperature of the injection chamber can be programmed to create a gradient, e.g. from 20 up to 300°C, in a few tens of seconds (Figure 2.6). So, the advantages of split/splitless injection are combined with those of cold injection onto the column. The advantages are:

 Absence of discrimination due to the needle.

 Use of classic syringes.Figure 2.6 PTV injector, with programmable temperature and cold on‐column injector. To make fast temperature gradients, the injection chamber is surrounded by a heating element or cooled by the circulation of a cold gas.

 Elimination of the solvent or low‐boiling point compounds.

 Larger injection volume.

The three principal modes of operation are named split cold injection, splitless cold injection and injection with elimination of solvent.

Split cold injection: the sample is introduced into the cold vaporization chamber. The vent valve is then immediately opened and the injector is heated. As the sample is not instantaneously vaporized, the solvent and the different compounds penetrate the column in the order of their boiling points. In this way, the column is never overloaded.

Splitless cold injection: this mode is employed for trace analysis. The vent valve is closed during injection. The injection chamber is then heated in order to transfer the sample into the column, which is maintained cold.

Injection with elimination of solvent: the sample is introduced into the cold injector, after which the vent valve is opened. The vent flow rate is very high and can reach 1,000 ml/min in order to eliminate all of the solvent. The injector is then heated to permit transfer of the less volatile compounds onto the column, with the vent valve now being closed (splitless mode). In this way, it is possible to inject up to 50 μl in a single injection or up to 500 μl of sample solution in a volatile solvent, over several injections. This method eliminates the preliminary concentration step of the sample prior to injection.

Injection after pyrolysis. Solid samples that are not soluble in solvents may nevertheless be the subject of a GC analysis by placing a device upstream from the injector. This device brings the sample to 600°C to decompose it into smaller molecules. The composition of these molecules will be used to identify the starting sample. The related injector is generally of the PTV type. This method is used for polymers, paints, rubber, additives or textiles.