Separation capillary columns

Figure 3.8 Second-dimension chiral cyclodextrin capillary column separation of a non-racemic pair of nonachlorobomane compounds extracted from dolphin blubber, shown with expanded attenuation in the inset. The primary separation (not shown) was performed on an apolar primary capillary column. Reproduced from H.-J. de Geus et al. J. High Resol. Chromatogr. 1998, 21, 39 (59).

Capillary column separation of some constituents of human urine. 

To meet the high demands of organic trace analysis,21 GC columns have been subject to continuous refinement. This refers not only to the reduction in diameter of the nowadays almost exclusively used capillary columns (separation efficiency increases with decreasing capillary diameter), but also reflects the development in stationary phase technology In order to reduce column bleed (which is essential for mass spectrometric detection), highly cross-linked stationary phases are used to... 

Gas-solid chromatography (GSC) and gas-liquid partition chromatography (GLC) are variations of GC. In GSC separations occur primarily by differences in absorption at the solid phase surface. In GLC a nonvolatile liquid is coated or chemically bonded onto particles of column packing or directly onto the wall of a capillary column. Separation occurs primarily by differences in solute partitioning between the gaseous mobile phase and the hquid stationary phase. 

A good comparison of packed and glass capillary column separations was demonstrated by Grob (8). The two chromatograms shown in Figure 6 are of the same lake water extract, run on the same stationary phase (OV-1). Packed and wall coated open tubular (WCOT) columns and methods are compared in Table I. 

Figure 6. Comparison of packed and capillary column separations of a river water extract. Dotted lines indicate corresponding sample com-...

Figure 8. High capacity capillary column separation of a black pepper oil extract. Column was 70 m X 0.9 mm i.d. with Carbowax 20M, and was temperature programmed from 50° to 170° C. (9)...

The figure shows major components were separated in less than three minutes. A pressure ramp of 100 bar/min starting at 75 bar was utilized, demonstrating the high speed capability of capillary column separations. Figure 17 shows the mass spectrum of palmitoyl-disteraroylglycerol (MW = 862) obtained during the capillary SFC... 

Separators. As long as packed columns with high gas-flow rates were used, it was necessary to separate the carrier gas from the analytes. This was accomplished by a variety of devices called separators examples include the Biemann-Wat-son separator and the jet separator. The latter was subsequently used in LC/MS interfaces. Due to the replacement of packed GC columns by capillary columns, separators are no longer used they are described in detail in [16]. 

Figure 3.67 Separation of common inorganic anions and poiarizabie anions on an lonPac AS20 capillary column. Separator column lonPac AS20 column dimensions 250 mm x 0.4 mm i.d. column temperature 40 °C eluent ...

The ramp rate governs the tradeoff between analysis time and resolution. The compromise between resolution and time of analysis is contrasted in Figure 3.64 for parallel capillary column separations of lemon oil generated at three different programming rates. Relying on experience and intuition in establishing optimum column temperature conditions can be time-consuming and inefficient. An alternative route is the use of computer simulation for method development this approach is discussed in much further detail in the next chapter (98-102). 

This simple illustration shows how the basic choice of capillary versus packed columns determines the nature of the resulting separation and how optimization of flow and temperamre can produce further improvements. Now we will leave packed columns behind and consider in more detail the various avenues available for optimization of capillary-column separations. 

Fig. 4. Examples of gas chromatographic separations on capillary and packed columns, (a) Packed column separation of mixed hydrocarbons (b) capillary column separation of some flavor compounds. Reproduced from D.W. Grant, Capillary Qas Chromatography, 1996. John Wiley Sons Ltd. Reproduced with permission.

Figure 2.123 Simulation of a packed column separation performed on a 30 m capillary column. Carrier gas has been changed from nitrogen to helium and compared with a 3% OV17 packed column, the 5% phenyl-methylpolysiloxane capillary column separates four previously unresolved peak pairs in a similar run time. Column 30 m TRACE...

This test method provides sample clean up and instrumental conditions necessary for the determination of Aroclors. Gas chromatography (GC) using capillary column separation technique and electron capture detector (BCD) are described. Other detectors, such as atomic emission detector (AED) and mass spectrometry (MS), may be used if sufficient performance (for example, sensitivity) is demonstrated. 

Berg et al. [67] separated PCBs from chlorinated insecticides on an activated carbon column prior to derivatisation and gas chromatographic separation on a capillary column. Separation is based on the observation that PCBs adsorbed on activated charcoal cannot be removed quantitatively with hot chloroform but can be with cold benzene. Insecticides of the DDT group and a variety of others (eg g-BHC, Aldrin, Dieldrin, Endrin and Heptachlor and its epoxide) can be eluted from the charcoal with acetone-ethylether (1 3). Typical recoveries from a mixture... 

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