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The separation of the DBD–Met and DBD–Ate isomers are shown in figure 49 (chromatogram A, DBD–Met and chromatogram B, DBD–Ate). Each enantiomeric pair represents 50 pmol of the original drug. The separation was carried out on the CHIRACEL OJ-R column (15 cm long, 4.6 mm I.D., packed with particles 5 mm in diameter coated with the cellulose ester. The mobile phase used for the separation of DBD–Met was methanol/acetonitrile : 90/10 v/v, at a flow rate of 0.5 ml/min., the separation ratio was 1.33. The mobile phase used for the separation of DBD–Ate was methanol, also at a flow rate of 0.5 ml/min., the separation ratio being 1.53. The excitation wavelength was 450 nm and the emission wavelength was 560 nm. The fluorescent derivatives were found to be stable at 4˚C for over 1 week. Courtesy of the Royal society of Chemistry, Ref. [12]   Figure 49 The Separation of Derivatized Metoprolol and Atenolol at High

.   The Analysis of Gasoline   Gasoline is a multi-component hydrocarbon mixture of which many of the components have very similar molecular weights and all have interactive properties that are almost exclusively dispersive (with the exception of the aromatic hydrocarbons that can interact by induced dipoles if the stationary phase is strongly polar). The structure of many of the hydrocarbons components are also very similar and the mixture contains many isomers. It follows that the separation factors between individual components are likely to be very small and, consequently, to achieve a separation, columns of very high efficiency will be essential.   Open tubular columns are ideal for this type of separation and, in fact, it is impossible to separate gasoline efficiently with a packed column, (and that will be true even if the column is 50 ft long and the inherent long analysis times could be tolerated). As the separation demands a large number of theoretical

to ensure a separation of (6s) for the two enantiomers can be calculated over a range of temperatures and solvent compositions. Figure 22. Graphs of Required Efficiency against Temperature for Each Solvent Composition Curves relating required efficiency against temperature for each solvent composition, calculated in this manner, are shown in figure 22. As would be expected, the minimum efficiency is required at the lowest temperature and lowest ethanol concentration. As either the separation ratio and/or the capacity ratios decrease, the necessary efficiency to achieve a separation increases (as predicted by equation (39)). At one extreme, where the capacity ratio is very small (i.e. at 50% v/v ethanol and 50˚C), 15000 theoretical plates is necessary for separation. However, if the volume fraction of ethanol is set at 0.05, then even at 50˚C, separation is achieved with less than 3000 theoretical plates.      

The first fraction of the second separation is bulked with the original mixture and recycled. An analytical separation of fraction 2 of the second separation is shown in figure 40. The separation was carried out under the same conditions as those shown in the separation in figure 38. It is seen that the second enantiomer is also obtained in a state of high purity and furthermore because the third fraction is recycled there is little loss of material   Courtesy of ASTEC Inc.   Figure 40. The Second Preparative Separation of the Isomers of Nicardipine

nbsp; Courtesy of Supelco Inc.   Figure 46 The Separation of Some Aromatic Hydrocarbons The separation of some aromatics contained in a mixture of hydrocarbons is shown in figure 46. A column 30 m long, 0.25 mm I.D., carrying a film of permethylated b-cyclodextrin 0.25 mm thick, was used by Supelco for the separation. The column was operated isothermally at 50˚C and helium was use as the carrier gas at a flow velocity of 20 cm/s. It is seen that baseline separation is achieved for the m- and p-xylenes and that the separation ratio for the two isomers was about 1.03

isomers is an excellent example of the type of separation for which the recycling technique is particularly useful. The chromatogram shows the results obtained from three complete elution cycles. In the first cycle, although separation has begun, there is little or no visible resolution. It should also be noted that the peak is distinctly asymmetrical. On the second cycle, the two enantiomers are beginning to separate and the asymmetry is at least as bad if not worse. In the third cycle, the separation is improved still further, and is sufficient to allow the collection of significant quantities of the individual isomers at a high purity despite the asymmetry. It is also seen that the process is fairly rapid as three cycles are completed in less than 12 minutes. An additional example of the technique of recycling, which includes another collection procedure called peak shaving, is shown in figure 21 which depicts the preparative separation of the enantiomers of 5-methyl-5-