Chromatograms produced from the

Figure 4, Chromatograms produced from the oxygen absorption of...

The data of Table III represent calculated bandwidths and efficiencies. Actual realized efficiencies were measured for the four chromatograms of Figure 4. For the 10-ym gel column, the conventional system produced an effective efficiency of 11,000 plates, compared with an effective efficiency of 16,000 plates for the optimized systems. These values are in excellent agreement with the calculated values shown on the top line of Table III. Similar measurements on chromatograms obtained from the 5-vim gel columns yielded values of 16,000 and 20,000 plates, respectively, for the conventional and optimized systems. This also represents good agreement with calculated effective efficiencies at total exclusion for a 24,000 plate column. 

The structures of some corticosteroids listed in order of their elution from an ODS column eluted with a methanol/water (75 25) mobile phase and below the chromatogram produced by the mixture. 

Figure Gl.7.lisa comparison of chromatograms from a solid-phase microextraction (SPME) from a beverage in a sealed container and from the same beverage in a mouth simulator. This comparison demonstrates that a very different volatile ratio is produced from the same food under different sampling conditions. Due to these differences, it is important to use a sampling method that simulates mouth conditions when studying flavor compositions that produce a human perception. Most methods intended to increase headspace volatile concentration, such as adding salt for salting out, do not uniformly affect volatility. For some compounds,...

In addition, the mixing of two or more accelerants may produce a sample that is virtually impossible to identify. The chromatogram produced from such a sample is difficult to associate with a single original accelerant or with a known mixture of accelerants prepared by the forensic chemist since he is estimating the ratios of accelerant mixtures he suspects to be present in the questioned sample. 

Pyrolysis of polystyrene produces an oil very high in concentration of the monomer, styrene and also other aromatic compounds. Eigure 11.15 shows a typical gas chromatogram for the pyrolysis oil produced from the pyrolysis of polystyrene, showing... 

Fig. 2.3 shows the use of an additional parameter that helps the generation of fast shallow gradients that of elevated temperatures. It shows the chromatogram produced from a run made with a 50 x 2.1 mm column of 3 pm SymmetryShield RP-18 operated at 60°C with a flow of 1.5 ml/min and a gradient time of 5 min. The resultant re.solution value was 62. The increased temperature used in this run causes a sharp reduction of the viscosities of the solvents used in the mobile phase, without significant loss in column efficiency [8], although changes in selectivity can be anticipated and exploited 19-121-... 

Jet fuel is kerosene-based aviation fuel. It is medium distillate used for aviation turbine power units and usually has the same distillation characteristics and flash point as kerosene. Jet fuels are manufactured predominately from straight-run kerosene or kerosene-naphtha blends in the case of wide cut fuels that are produced from the atmospheric distillation of crude oil. Jet fuels are similar in gross composition, with many of the differences in them attributable to additives designed to control some fuel parameters such as freeze and pour point characteristics. For example, the chromatogram (Figure 27.4) of a commercial jet fuel (Jet A) is dominated by GC-resolved n-alkanes in a narrow range of n-C-j to n-Cig with maximum being around n-Ci. The UCM is well dehned. 

Figure 3 shows the pump cycle for a chromatogram different from the one considered in the previous section. The fundamental of the pump cycle in this case is 1128/6720. The shape of the pump cycle is shown every 50 periods, which is approximately every 300 seconds. In the figure, successive traces are offset by 1 nS/cm. The shapes shown are typical of those produced by the two piston pump that we used. This chromatogram shows considerable instability. The pump cycle in the chromatogram considered in the previous section is much more stable as is the pump cycle in another chromatogram that we consider in detail below. If the pump cycle is unstable, then an estimate such as p(t) may be more appropriate for the removal of the pump cycle than the estimate used in the previous section. 

On completing the analysis, the output from any diode can be selected and a chromatogram produced displaying the adsorption of the light... 

Fig. 102. Gas chromatogram of the methane produced from the alkali fusion of GE Viscasil 60,000 polydimethylsiloxane.

Figure 3.14 Alkali fusion reaction gas chromatogram produced from (a) polyamide-imide (PAI-2). The column temperature was programmed from 100 to 250 °C at 12 C/min (b) polyamide terpolymer (PT3). The column temperature was programmed from 100 to 250 °C at 12 °C/min. Reprinted with permission from S.P. Frankoski and S. Siggia, Analytical Chemistry, 1972, 44, 3, 507. 1972, ACS) [160]...

Detection and result The chromatogram was freed from mobile phase (heated to 110°C for 30 min) and then exposed to bromine vapor for 1 h in a chamber, after blowing off excess bromine from the layer it was immersed for 1 s in the reagent solution. On drying in air dibutyltin dilaurate hRf 25 — 30), dibutyltin dichloride (kR( 25 — 30), dioctyltin oxide (hR( 40), tributyltin oxide (hRf 80), tributyltin chloride (hRf 80) and tetrabutyltin (hRf 85-90) produced persistent blue zones on a yellow ochre background (Fig. 1). 

The detector. The function of the detector, which is situated at the exit of the separation column, is to sense and measure the small amounts of the separated components present in the carrier gas stream leaving the column. The output from the detector is fed to a recorder which produces a pen-trace called a chromatogram (Fig. 9.1fr). The choice of detector will depend on factors such as the concentration level to be measured and the nature of the separated components. The detectors most widely used in gas chromatography are the thermal conductivity, flame-ionisation and electron-capture detectors, and a brief description of these will be given. For more detailed descriptions of these and other detectors more specialised texts should be consulted.67 69... 

Some detectors can give additional information about the elutes (the eluted solutes). One example is the gas chromatograph—mass spectrometer (GC-MS), which produces a mass spectrum of each compound as well as its mass and location in the chromatogram. This powerful means of detection can be used when standard samples are not available to help determine the identities of the solutes. A beam of ions bombards each compound as it emerges from the chromatograph. The compound breaks up into ions of different masses, providing a spread of narrow peaks instead of one peak for each compound. The relative amount of each fragment is determined and used to help identify the compound. 

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