Cold splitless injection

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. 

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... 

Cold splitless WCOT thick film Idem Reproducible and accurate sampling Controlled evaporation No discrimination on basis of b.p. Large volume injection Low detection limits Minimisation of solvent entering column Allows polar solvents Automation Small sample size introduction (<2 xL) Thermal degradation possible (long residence times of components in liner)... 

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]. 

Splitless injection reconcentration of the bands broadened in time requires either lowering of the column temperature at least 60-90°C below the elution temperature of the solutes of interest (cold trapping) or keeping of the column at least 20-25 °C below the solvent boiling point to create solvent effects. 

R. Snell, J. Danielson, et al., Parameters affecting the quantitation performance of cold on-column and splitless injection systems used in capillary gas chromatography, J. Chromatogr. Sci., 25 225-230 (1987). 

H. Stan and H. Muller, Evaluation of automated and manual hot splitless, cold-splitless (PTV) and on-column injection technique us-... 

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. 

When the extracted analytes are to be retained directly on the chromatographic column or at the retention interface, their insertion can be accomplished in various ways, namely (a) by injection into the column, whether directly (SFC, GC) or with the aid of a cooling system (GC, HPLC) (b) by split-splitless injection (SFC, GC) (c) by using a programmed temperature vaporizer (GC) or (d) by injection into a cold trap and subsequent thermal desorption (GC) or elution (HPLC). 

This injector, named PTV programmed temperature vaporizer), is conceptually similar to the split/splitless model. The temperature of the injection chamber can be programmed to effect a gradient, e.g. from 20 up to 300 °C, in a few tens of seconds (Figure 2.6). So, the advantages of the split/splitless injection are combined with those of the cold injection onto the column. 

When properly installed, the analytical system involving thermodesorption cold trap injection and two-dimensional chromatography can be used routinely for analysis of the stereoisomers of soman and sarin in blood and tissue samples at minimum detectable concentrations of 1 -5 pg of stereoisomer per ml blood or gram tissue. In recent toxicokinetic experiments in pigs, the analytical system comprised chiral gas chromatography on a Chirasil-L-Val column with splitless injection and detection... 

Splitless injection is used for dilute samples and means introducing most of the sample into the column. Injector temperature is lower and the residence time of the sample in the injection port is longer (approximately one minute), so solvent trapping or cold trapping may be required. It is used when sensitivity is most important. 

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... 

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