Open-tubular trapping

Figure 2.21 shows the on-line extraction gas chromatogram of 2.25 ml of water spiked at 5 ppb levels with 14 different organic pollutants (40). In this case, the authors concluded that wall-coated open tubular traps (thick-film polysiloxane phases) can be used for the on-line extraction of organic compounds from water. However, when using swelling agents such as pentane, non-polar analytes can be trapped quantitatively, while for more polar compounds chloroform is the most suitable solvent. 

H. G. J. Mol, H.-G. Janssen and C. A. Cramers, Use of open-tubular trapping columns for on-line extr action-capillar y gas cliromatography of aqueous samples , 7. High Resolut. Chromatogr. 16 413-418 (1993). 

OTT Open-tubular trapping PI-ToF Photoionisation time-of-flight... 

Figure 2.21 A gas chromatogram of a sample of river water (2.25 ml) spiked at 5 ppb levels with 1, toluene 2, ethylbenzene 3, methoxybenzene 4, p-dichlorobenzene 5, dimethylphe-nol 6, dimethylaniline 7, chloroaniline 8, indole 9, dichlorobenzonitrile 10, trichlorophe-nol 11, dinitrobenzene 12, trifluranil 13, atrazine 14, phenanthrene. Reprinted from Journal of High Resolution Chromatography, 16, H. G. J. Mol et al., Use of open-tubular trapping columns for on-line extraction-capillary gas chromatography of aqueous samples , pp. 413-418,1993, with permission from Wiley-VCH.

OTT Open tubular trap As in-tube (micro)extraction Uses not restricted to liquid-phase separation the name suggests preferential use in conjunction with GC for volatile compounds... 

In SFE-LC, the most common interfrce is based on solid-phase trapping 2.15,44,58-63,66-68,70-80), although a few other types of interfrices such as impactor interfrce 69) open-tubular trapping 64) and the sample loop interface (65) have been developed as well. Direct trapping into a conventional packed LC column is not possible because of the high back pressure that analytical columns create. Because of the back pressure, the fluid cannot be efficiently decompressed and thus it will retain (partially) its solvation properties and efficient trapping will not be achieved, especially if modifiers are used in the... 

Fig. 23-2. Two examples of traps. A shows a trap packed with Porapak N cooled to -15 °C with air from a Vortex tube and heated during desorption by an electrical current through the trap. B shows an open tubular trap cooled in the vapours of liquid nitrogen. The trap is heated for desorption of the halocar-bons either by immersing it into boiling hot water or by an electrical current through the tube. See text for details.

Figure 23-2 shows two examples of cold traps, one packed and one an open tubular trap. In both cases the gas flows through the trap in one direction during the purge phase and in the opposite direction when the trap is heated and the halocarbons desorbed, i.e., the halocarbons are back-flushed out of the trap. The back-flushing ensures that band sharpening is maintained, and that no accumulation of heavier compounds in the trap will cause its deterioration. 

Fig. 23-3. A chromatogram of the entire range of halocarbons from an analysis of southern ocean surface seawater according to the Halocarbon mode described in detail in the text. The upper part of the figure illustrates the timing of events (time axis not to scale). An open tubular trap as shown in Fig. 23-2 heated in boiling water was used.

Fig. 23-4. A chromatogram from a surface seawater sample analysed according to the Tracer mode utilising the pre-column to get a heart-cut chromatogram (see text for details). The time axis (not to scale) is illustrated in the upper part of the figure. An open tubular trap as in Fig. 23-2 B heated in boiling...

Solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE) are most implemented in water quality-control laboratories. Other sorptive extraction techniques (such as open-tubular trapping, gum-phase trapping extraction, and equilibrium gum-phase extraction) are reviewed in Ref. [160]. 

The contents of the lower half of Table 1 show that there is one approach based on solvent extraction (that is briefly discussed below) and there are four alternatives based on liquid-solid sorption. Three of these are closely related, i.e., SPE, SPE thermal description (SPETD), and open tubular trapping (OTT), and are discussed in this chapter. The fourth, solid-phase microextraction (SPME), will be discussed separately in Chapter 8. 

Another possibility to extract anal34es from an aqueous phase is by retaining them in the stationary phase of an open tubular trapping (OTT) column, which essentially is a piece of GG column. After enrichment from 0.2 to 10 ml of water, clean up with 0.15 to 0.5 ml distilled water and removal of the water by a slow... 

---