Split cold injection

For large volume injection the PTV injector can be operated as a cold split injector with solvent elimination, as a splitless injector with vapor discharge, or as a hot splitless injector using vapor overflow for solvent elimination. In cold split injection, the sample is introduced into the injector at a temperature below the solvent boiling point with the... 

In injection moulding, polymer granules are compressed by a ram or screw, heated until molten and squirted into a cold, split-mould under pressure (Fig. 24.3b). The moulded polymer is cooled below T, the mould opens and the product pops out. Excess polymer is injected to compensate for contraction in the mould. The molecules are oriented... 

Cold split Column independent 100-fold increase in sensitivity with respect to conventional GC injection Reproducible and accurate sampling Controlled evaporation No discrimination on basis of b.p. Rapid transfer of sample to column Low volume of CIS liners (2-3 xL)... 

Splitless injection is required for very dilute solutions. It offers high resolution but is poor for quantitative analysis because less volatile compounds can be lost during injection. It is better than split injection for compounds of moderate thermal stability because the injection temperature is lower. Splitless injection introduces sample onto the column slowly, so solvent trapping or cold trapping is required. Therefore, splitless injection cannot be used for isothermal chromatography. Samples containing less than 100 ppm of each analyte can be analyzed with a column fdm thickness < 1 p.m with splitless injection. Samples containing 100-1 000 ppm of each analyte require a column film thickness 1 p.m. 

Splitless, direct, and cold-on-column techniques all utilize the solvent effect to maximize sample loading and minimize sample band widths. There is a wealth of information on how to best utilize the solvent effect to minimize the starting sample bandwidths in the splitless mode of injection. Several articles review the proper use of the solvent effect [31-36]. Splitless injection is ideal for dilute clean samples it, however, is not suited for heat-sensitive samples. Classical split injection is discussed in a comprehensive review recently published [37]. The solvent effect in split injection has been discussed in two articles [38,39]. 

Schomburg, G., Husmann, H., Behlau, H., and Schultz, F. (1983). Cold sample injection with either split or splitless mode of temperature programmed sample transfer. Proc. Int. Symp. Capillary Chromatogr. 5th pp. 280-284. 

Another method of reconcentrating the components at the head of the column is to keep the column temperature low enough to condense the solutes (cold trapping).A general guideline for the use of this precolumn concentration technique is that compounds with boiling points 100°C higher than the column temperature will be cold trapped. Therefore, splitless injection should be used when component concentrations are too low for detection by split injection (<0.1% sample) or when only a very limited amormt of sample is available. 

Figure 3.7. Large volume injection of 100 (il of a mixture of n-alkanes of wide volatility using the PTV injector in the cold split solvent elimination mode. The vaporizing chamber was thermostated at 0°C, split flow 250 ml/min with the split vent closed after 2.5 min. For splitless transfer the vaporizing chamber was heated at 4°C/s to 325°C with the puige flow started after 1.5 min. (From ref. [68] Wiley-VCH).

In injection moulding, plastic granules are heated until they have a sufficiently low viscosity to be injected under pressure into a cold, split mould. The shaped plastic is cooled and released. 

For cold splitless injection, the sample is introduced into the vaporizing chamber at a temperature close to the solvent boiling point with the split vent closed. Shortly after sample introduction, the injector is rapidly heated to the temperature required to transfer the sample into the column, and the vaporization chamber purged of solvent residues by opening the split vent. Similar to hot splitless injection, cold trapping and solvent effects are employed as refocusing mechanisms. 

There are many advantages of cold split and splitless sample injection ... 

All other PTV adjustments of time and temperature are completely unchanged compared with total sample transfer Of particular importance for the split injection using the PTV cold injection system is the fact that the sample is injected into the cold injector (see also Section 2.2.7.5). The choice of start temperature of the G C oven is now no longer coupled to the boiling point of the solvent because of the solvent effect and is chosen according to the retention conditions (Tipler and Johnson, 1989). 

Certainly, the precision and accuracy of the PTV techniques are generally superior to those of the classical hot split and splitless techniques and approach those obtained by cold on-column Injection [ 34,36,37, -54-57,62,64]. However, less is known concerning optimization of PTV injection and probably more parameters have to be considered than for cold on-column injection. The latter is, consequently, the preferred injection technique for most samples, except those contaminated by larg< amounts of involatile Impurities and for headspace vapors. 

Figure 3.3 Discriaination of n-alkanes depending on injection technique. A, filled needle B, hot needle C, cold on-coluan. A and B were obtained using a 1 40 split. Saaple n-alkanes 1 10,000 in hexane. (Reproduced with peraission froa ref. 24. Copyright Dr. Alfred Huethig Publishers). ...

Solvent venting, without splitting Liquid sample from syringe into cold inlet. Solvent is vented at low temperature, condensing nonvolatiles. Heat programming subsequently vaporises the residues, which enter column as in splitless injection Dilute samples thermally labile Broad, some focusing required 1-1000 80-95... 

The advent of high-resolution capillary gas chromatography (HR-CGC) with on-column injection has resulted in improved GC analysis of polymer additives [92-94]. The solution of the additive mixture is injected directly into the cold end of the capillary column by means of a cold injector. Thus, sample discrimination, the instantaneous evaporation of the sample solvent, is avoided. The nonvaporising, on-column injection combined with very high resolution of the capillary columns allows accurate separation, identification and quantification of additives of complex mixtures. With the solvent venting technique, the sample is introduced into the column without splitting and sample concentrations... 

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