Stationary-phase column chromatography

Resolution of a racemic mixture is still a valuable method involving fractional crystallization [113], chiral stationary phase column chromatography [114] and kinetic resolutions. Katsuki and co-workers demonstrated the kinetic resolution of racemic allenes by way of enantiomer-differentiating catalytic oxidation (Scheme 4.73) [115]. Treatment of racemic allenes 283 with 1 equiv. of PhIO and 2 mol% of a chiral (sale-n)manganese(III) complex 284 in the presence of 4-phenylpyridine N-oxide resulted... 

FIGURE 1.4 Optical micrograph of macroporous chromatographic column materials, (a) Monosized particles of 20 tm. (b) Commercial column filling of 12-28 tm. [Reprinted from T. Ellingsen et al. (1990). Monosized stationary phases for chromatography.7. Chromawgr. 535,147-161 with kind permission from Elsevier Science-NL, Amsterdam, The Netherlands.]... 

Recently, Janjic et al. published some papers [33-36] on the influence of the stationary and mobile phase composition on the solvent strength parameter e° and SP, the system parameter (SP = log xjx, where and denote the mole fractions of the modiher in the stationary and the mobile phase, respectively) in normal phase and reversed-phase column chromatography. They established a linear dependence between SP and the Snyder s solvent strength parameters e° by performing experiments with binary solvent mixtures on silica and alumina layers. 

Kang, W. et ah. Analysis of benidipine enantiomers in human plasma by liquid chromatography—mass spectrometry using a macrocyclic antibiotic (vancomycin) chiral stationary phase column, J. Chromatogr. B, 814, 75, 2005. 

As in gas chromatography, the elution time of a compound can be described by the capacity factor, k, which depends on the chemical nature of the composition and flow rate of the mobile phase, and the composition and surface area of the stationary phase. Column length is an important determinant of resolution. Only compounds having different capacity factors can be separated by HPLC. 

Poly(octadecylsiloxane) is often used in chromatography to prepare reversed phase column material. The process which takes place during a chromatographic run is closely related to the enrichment process described here i.e., materials which are employed to provide stationary phases for chromatography may also be used for preparing enriching membranes. This material gives rise to fewer absorption bands than PDMS but more than PE. 

The stationary phase in chromatography is fixed in piace either in a column or on a planar surface. 

Chromatography is a powerful separation method because it can be carried out easily under experimental conditions such that the two phases of the system are always near equilibrium. This is because the kinetics of the mass transfers between these phases is usually fast. The separation power of a column, under a given set of experimental conditions, is directly a function of the rate of the mass transfer kinetics and of the axial dispersion coefficient. The scientists involved in the development of stationary phases for chromatography have produced excellent packing materials that permit the achievement of a very large number of equilibrium stages (i.e., theoretical plates) in a column. Thus, as we show later in Chapters 10 and 11, the thermodynamics of phase equilibria is often the main... 

The efficiencies of imprinted polymers used as stationary phases in chromatography are often greatly improved when used in capillary electro chromatography columns. These polymers are usually produced in the column, by attaching the imprinted polymer to the fused silica wall [27-30]. This is often done by derivatizing the column wall with a silylated monomer such as [3-(methacryloyloxy)propylj-trimethoxysilane, or adsorbing an initiator to the surface [31-34] as illustrated in Fig. 6. 

Silica particles with grafted PNIPAM shell were used as a stationary phase for chromatography columns. The temperature sensitivity of PNIPAM can be used to tune the hydrophilic/hydrophobic balance in the chromatography column and to increase considerably the separation of steroids, peptides, and proteins. 

Under a nitrogen atmosphere, a hexane solution of butyllithium (650 pL, 1.00 nunol) was added to bromobenzene (157 mg, 1.00 mmol) in Et20 (0.5 itiL) at 0 X. The mixture was stirred at room temperature for 1 h and then cooled to -78 °C. Trimethoxyborane (104 mg, 1.00 mmol) was added to the reaction mixture. The mixture was stirred at -78 C for 30 min and then at room temperature for 1 h. To the mixture were added H2O (18 mg, 1.00 mmol), isopropyl tra s-2-hexenoate (262) (62 mg, 0.40 mmol), and a solution of Rh(acacXC2H4)2 (3.1 mg, 12 pmol) and (S)-BINAP (9.0 mg, 14 pmol) in dioxane (2.0 mL). The whole mixture was heated at 100 C for 3 h. Addition of saturated aqueous sodium bicarbonate followed by ethyl acetate extraction and chromatography on silica gel (hexane ethyl acetate = 10 1) gave 90 mg (96% yield) of isopropyl 3-phenylhexanoate 264 as a colorless oil. HPLC analysis was performed on a Shimadzu LC-9A (Shimadzu Corp. Nakagyo-ku, Kyoto, Japan) and a JASCO PU- 980, with a JASCO UV-970 UV detector (Jasco Inc., Easton, MD, U.S.A), liquid chromatographic system with chiral stationary phase columns Chiralcel OD-H, OJ and OG, (95% ee). ... 

As noted in the discussion of TLC, the strength of the adsorption of an organic compound to the solid support depends on the polarity and nature of the adsorbent as well as on the nature of the functional groups present in the molecule. When normal-phase column chromatography is performed, a polar stationary phase such as alumina or silica gel is used in combination with organic solvents as the mobile phase or eluant. Under these conditions, the elutropic series described for TLC in Section 6.2 applies. 

In reverse-phase column chromatography, the packing material for the stationary phase consists of glass beads coated with a nonpolar hydrocarbon film. 

In reverse-phase column chromatography, which phase is the more polar the stationary phase or the mobile phase ... 

A mixture containing compounds 9-11 was separated by normal-phase column chromatography, using neutral alumina as the stationary phase and petroleum ether as the eluant. Predict the order in which 9-11 will elute from the column. 

---