Amino-phase packing

The data of Fig. 11 thus indicate that restricted-access delocalization does not exist for amino-phase packings. Furthermore, the importance of the variation of eo with 6n, shown in Fig. 11, is insignificant, so far as calculations of e" are concerned. We will therefore assume that cb is constant for a given solvent B and amino-phase packings, in the calculation of ° for multicomponent mobile phases (Appendix). 

Terminal amino groups are believed to comprise adsorption sites on the surface of amino-phase packings (77). These (1) Eire exposed for direct interaction with adsorbate molecules, (2) are not rigidly positioned on the surface, and (3) have a much lower surface concentration (2-3 /xmol/m ). These characteristics of the various LSC packings so far discussed are summarized in the surface representations shown in Fig. 14 for each adsorbent. The m or adsorption sites in each case are indicated by enclosure within a circle (except the vacancy site for alumina, shown as an asterisk in Fig. 14). 

A mixture of acetonitrile and water is capable of separating sugars on amino phase. Problems with the determination of reducing sugars can occur, since the reaction of the keto group with the amino moiety is well known. In a similar way, an amino phase in normal-phase mode should not be used with acetone. NH2 packing can be used as a weak anion exchanger. The diol... 

Of the polar bonded-phase packings that have been investigated, the interactions between carotenes and nitrile stationary phases are very weak thus the limitations described for silica apply (164). Amino-bonded phases eluted with iso-octane containing 0.5% stabilized tetrahydrofu-ran separate a- and /3-carotene (unresolved) from y-carotcnc canthaxanthin and /3-cryptoxanthin are not eluted (161). The cis isomers of /3-carotene are separated from the all-trans isomer thus amino columns offer an alternative option to alumina columns for determining all-trans-/3-carotene without its cis isomers interfering. 

Reversed-phase separation [6] of polar and non-polar PTH-amino acids may be accomplished using Corasil-Cig bonded phase packing (particle diameter, 37-50 jum) and eluting with water-acetonitrile-isopropanol (100 1.5 1). An example of the reversed-phase separation of sixteen PTH-amino acids is given in Fig.4.4. The limit of detection of... 

Shinbo, T., Yamaguchi, T., Nishimura, K., and Sugiura, M. (1987) Chromatographic Separation of Racemic Amino Acids by Use of Chiral Crown Ether-coated Reversed-phase Packings, J. Chromatogr. 405, 145-53. 

Site-competition delocalization of solutes X has been observed for adsorption of localizing solutes X onto silica and amino-bonded-phase packings, but not for alumina (/, 17). We will comment on this later. 

T. Shimbo, T. Yamaguchi, K. Nishimura, and M. Sugiura, Chromatographic separation of racemic amino acids by use of chiral crown ether-coated reversed-phase packings,/. Chromatogr 405 (1987), 145. 

Toda procedure for obtaining enantiomeri-cally pure compounds will find broad application very soon. This development could make preparative HPLC with chiral columns obsolete and be applied to distillable amino acid derivatives as well. After all, analytical resolution of amino acids was quite successful by host/guest complexation chromatography with reversed-phase packings loaded with Cram s chiral 1,1 -binaphthyl crown ethers (similar to 1). [20]... 

In a recent publication, Lindroth and Mopper (1979) have presented a method for precolumn derivatisation followed by separation on reversed phase packing materials with subsequent fluorimetric detection of the amino acid-derivatives. The method has been applied for the analysis of small volumes (100 jul or less) of seawater with separation of up to 25 amino acids within 25 min at sensitivities in the femtomolar (lO M) range. The speed of analysis together with the sensitivities attainable on a routine basis and the simplicity of the analytical instrumentation and procedure, makes the technique eminently suitable for real-time analysis in the field (Garrasi et al., 1979). It is certain that this approach is an exciting development in marine analytical organic chemistry and sets the standard for discovery of equivalent techniques to detect and quantify other biochemical compounds. 

Figure 6 Chiral HPLC separation of amino acid derivatives on imprinted stationary phases packed with Z-L-Glu-OH (a), Boc-L-phe-Gly-OEt (b), Z-L-Ala-L-Ala-Ome (c) Z-L-Ala-Gly-L-Phe-OMe (d). Mobile phase chloroform - acetic acid. Column 250 x 4.6 mm. Flow rate, 1 mL/min. Detection, UV 260 nm. Reproduced from Ref. 22, with permission.

Diamide Chiral Separations. The first chiral stationary phase for gas chromatography was reported by GH-Av and co-workers in 1966 (113) and was based on A/-trifluoroacetyl (A/-TFA) L-isoleucine lauryl ester coated on an inert packing material. It was used to resolve the tritiuoroacetylated derivatives of amino acids. Related chiral selectors used by other workers included -dodecanoyl-L-valine-/-butylamide and... 

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