Vaporizer injectors

Adsorption or catalytic decomposition of labile substances by the syringe needle can be a problem for some compounds using hot vaporizing injectors [25]. For open tubular columns deactivated fused silica syringe needles and cold on-column Injection techniques are used to minimize this problem. Alternatively, syringes fitted with a needle shroud for cold-needle injection can be used [26]. 

In addition, solute focusing is possible by maintaining a low initial temperature (e.g. 40 °C) for a long period of time (8-12 min ) to allow the mixture of decompressed carbon dioxide, helium gas and the solutes to focus on the GC column. The optimization of the GC inlet temperature can also lead to increased solute focusing. After supercritical fluid analysis, the SF fluid effluent is decompressed through a heated capillary restrictor from a packed column (4.6 mm i.d.) directly into a hot GC split vaporization injector. 

Figure 2.4 Direct vaporization injector used for packed columns. Typical schematic of a model employing a septum. Depending upon the function required a wide range of inserts exist. Right, a variety of self-sealing septum (the Microseal Merlin), which can he used thousands of times (reproduced courtesy of Agilent Technologies).

Another alternative to splitless injectors is the programmed-temperature vaporization injector (PTV). The design of this injector resembles that of a split/splitless injector, except that PTV has a lower internal volume and lower thermal mass, and as a result can be heated very rapidly. One of the... 

Submicroliter samples are needed for the capillary on-column injection technique. To counter a general scepticism following the development of this injection technique, excellent quantitative results have been reported [42). The major advantages of this injection procedure seem to be in minimizing thermal decomposition of labile compounds as well as the lack of sample discrimination toward the later eluting components. This latter problem, observed frequently with the vaporizing injector... 

The absolute injection volume can be difficult to determine when microsyringes are used with hot vaporizing injectors. At the time of injection the sample volume delivered... 

A recent analytical procedure by Flores et al. targeted the optimization of the interface performance in the online coupling of reversed phase liquid chromatography and gas chromatography (RPLC-GC) coupling by means of a horizontally positioned PTV (Programmed Temperature Vaporizer) injector. It improved the sensitivity achievable in the direct analysis of olive oil-mixtures with 5% or 12% of some virgin and refined hazelnut oils, respectively, based on the analysis of fil-bertone enantiomers within 30 min and without any kind of pretreatment. 

Characterization of olive oil volatiles by multi-step direct thermal desorption-comprehensive gas chromatography-time-of-flight mass spectrometry using a programmed temperature vaporizing injector. Journal of Chromatography A, Vol.1186, pp. 228-235, ISSN 0021-9673... 

Rgure 5 Programmed temperature vaporizer injector. (From Hinshaw JV and Seferovic W (1986) Programmed-temperature split-splitless injection of triglycerides comparison to cold on-column injection. Journal of High Resolution Chromatography 9 69-77.)... 

For normal split injection, the sample is introduced at a temperature below the solvent boiling point with the split exit open. Shortly after withdrawal of the syringe needle the injector is rapidly heated to a temperature high enough to ensure rapid evaporation of the least volatile sample components. Discrimination effects, which are common for hot vaporizing injectors, are virtually eliminated and the sample split ratio and split flow ratio are similar. 

Since liquids expand considerably when they vaporize, only small sample sizes are desirable, typically microliters. Syringes are almost the universal method for injection of liquids. The most commonly used sizes for liquids are 1, 5, and 10 microliters. In those situations where the liquid samples are heated (as in all types of vaporizing injectors) to allow rapid vaporization before passage into the column, care must be taken to avoid overheating that could result in thermal decomposition. 

Bosboom, J.C. Janssen, H.G. Mol, H.G.J. Cramers, C.A. Large-volume injection in capillary gas chromatography 9. using a programmed-temperature vaporizing injector in the on-column or solvent-vent injection mode. J. Chromatogr. A,... 

A programmed temperature vaporizer injector (PTV) basically is a spUt-splitless injector with temperature control, i.e.. the vaporizer chamber can be heated or cooled rapidly. Three types of large volume introduction techniques can be distinguished ... 

---