Injection solvent expansion volumes

Pulsed splitless Reduction of the residence time in the liner resulting in the decreased analyte degradation/adsorption and reduced matrix-induced response enhancement Larger injection volumes (limited by the liner size and solvent expansion volume) Potential transfer of nonvolatile matrix cx)mponents further into the column... 

For flash vaporization injection, the effect of injection speed, choice of solvent, and injector temperature greatly affect the solvent peak width. Injection of a low-boiling solvent at high injector temperatures can cause the entire expansion volume of the liner to be exceeded by the expanded solvent. It must be remembered that 1 pi of liquid solvent injected at 250°C at 10 psig head pressure is converted to some 200-1000 pi of gas. Thus, as the injection volume increases, the injection rate should be adjusted so as not to exceed the expansion volume available in the port liner. Generally, nonpolar solvents perform best in the direct flash mode. The injection rate should follow the following formula [26] ... 

Sample solvent effects on gas chromatographic analyses involve a very different set of considerations. For capillary GC, the effect of the injection solvent has been shown to affect injection precision caused by the expansion volume of the vaporized injection solvent. If the solvent evaporates too fast to a volume larger than the injector volume, then the rapid pressure increase in the injector can cause the sample to leak out through the septum, leading to poor injection precision (11,12). Different solvents have different expansion volumes and expansion rates, therefore proper solvent selection can overcome this problem. Other solutions are smaller injection volume, slower injection speed, or lower injector temperature (11). 

The injection port liner is used to minimize dead volume when a sample is injected. Several are shown in Figure 20-27. Those shown are 0.8 mm i.d. with an internal volume of 12 pL. The solvent expansion type prevents flashback when injecting large volumes of dilute samples. 

Use the correct liner for an injection mode select the inner diameter of a liner to be commensurate with solvent boiling point, solvent expansion, and injection volume when employing a vaporizing inlet. 

Understanding the relationships between inlet liner geometry, carrier gas flow, injection volume and solvent vapour volume is essential for optimizing splitless injections. Especially the expansion volume of the solvent used must be taken into account. The maximum liquid injection volume needs to be adjusted in the hot... 

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