Pyridine-related compounds, separation

Figure 14-6. Separation of pyridine-related compounds by HILIC. Chromatographic conditions Atlantis HILIC silica 3 pm, 150 x 4.6 mm. Mobile phase A 0.1 % phosphoric acid in D.I water. Mobile phase B Acetonitrile. Gradient at 95% B to 60% B in 7 min and then hold 8 min.

Many different solvent developers have been used in the separation of sugars and related compounds. Three of these, phenol-water, collidine-water, and 1-butanol-acetic acid-water,27 also commonly employed in the resolution of amino acid mixtures, are widely used. Other commonly used solvent developers are 1-butanol-ammonia-water, 1-butanol-ethanol-water,27 1-butanol-pyridine-water,61 ethyl acetate-acetic acid-water, and ethyl acetate-pyridine-water.26... 

The IR-spectra of 41 tobacco alkaloids and related compounds have been tabulated (S5). Nornicotine, nicotine, myosmine, nicotyrine, anabasine, anatabine, and dihydronicotyrine were separated from an extract of tobacco alkaloids by countercurrent partition (86). Thin-layer chromatography has been used to separate nicotine, nornicotine, anabasine, and nicotyrine (57). The use of gas chromatography to separate tobacco alkaloids has been studied. The retention times of 11 tobacco alkaloids on polyethylene glycol columns has been reported (88) and the effect of the column packing on the retention times of pyridine bases has been described (89). Mixtures containing pyrrolidine, piperidine, pyridine, and various alkylated pyridines have been separated using programed temperature control (90). 

Using the solvent system propanol-pyridine-acetic acid-water (15 10 3 12) on cellulose powder, TLC plates gave excellent separations of the water-soluble antibiotics according to Ito et al. A ninhydrin reagent or an oxidized nitroprusside reagent was used as the identification system. Based on and color, 20 basic antibiotics were separated. For six closely related compounds, in terms of Rp, the solvent system consisting of water-saturated butanol plus 2% p-toluenesulfonic acid was successful in differentiation. 

Trimethylsilylation began to receive real attention, however, only after Sweeley et al (1963) used HMDS and TMCS in pyridine to derivatize a wide range of sugars and related compounds for gas-liquid chromatographic separation. Prior to this, TMCS had also been used for derivatization of... 

Several attempts have been made to simplify the comparisons of retention times from column to column and compound to compound. The first and simplest is by E. Kovats Helv. Chim. Acta, 41, 1915, 1958) involving the use of hydrocarbons. The next was by L.J. Rohrschneider (J. Chromatog., 22, 6, 1966), who used benzene, ethanol, methylethyl ketone, nitromethane, and pyridine to characterize liquid phases. W.O. McReynolds J. Chromatog. Sci., 8, 685, 1970) improved upon this by using 10 compounds to relate over 200 liquid phases to squalene. The results indicated that many of the liquid phases behaved nearly the same and that really just a few were needed to separate all of the compounds. Kovats introduced a retention index, I, which is defined as ... 

X-ray difiFraction studies showed that diquat and paraquat were adsorbed in the interlayer spacings of montmorillonite clay with the planes of the pyridine rings parallel to the silicate sheets see paraquat in Figure 5) (30, 53). Adsorption of one compound over another was related to the charge separation on the ions and the surface charge densities of various adsorbents 29, 30, 55, 57). 

The second band of this series falls between 1588—1560 cm" Unlike the parallel benzene band it is usually of medium intensity and its appearance is not therefore necessarily related to conjugation. The separation of this pair of bands is about 40 cm" for 4-alkyl pyridines but about 20 cm" for the 2- and 3-compounds [41 ]. 

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