Contribution of the lipophilic buffer to chiral recognition under reversed-phase conditions

Abstract

SummaryA lipophilic buffered aqueous mobile phase, without organic modifier, was used for the high performance liquid chromatographic enantioseparation of D,L-lactic acid on a Merck ChiraSpher (250 mm x 4 mm i.d.) column in which the chiral selector is poly(N-acryloyl-S-phenylalanine ethyl ester) bonded to a spherical silica particle. The lipophilicity of the buffer was achieved by addition of triethylammonium phosphate, the 'ethyl' apolar chains of which dynamically modified the ChiraSpher stationary phase and increased its hydrophobic character. The ion-paired (cethyltrimethylammonium bromide) analyte enantioseparation was realized by hydrogen-bonding and dipole-dipole complexation on the ChiraSpher stationary phase, superimposed on simultaneous reversed-phase partitioning.

Mechanism of enantioseparation on zeolite-supported chiral stationary phases in the presence of lipophilic buffer

“…The role of the enantiospecific interaction of the SO in retention is thus reduced or lost and hence the overall retention (capacity factors) of both enantiomers decrease, with a simultaneous decrease of tx and R s also. As stated elsewhere [11], increasing the concentration of ion-pairing reagent initially caused k' to increase regularly and then, above a certain concentration of CTAB, to decrease ( Figure 4). The decrease possibly occurs because the CTAB modifies the zeolite residual silanol groups and alters the charge of the SO of the chiral stationary phase in a manner similar to that by the TEAP buffer, as described above.…”

“…The silanol group, with its unselective hydrogen-bonding properties, has generally been considered disadvantageous (hence the interest in endcapping or non-capping) but nowadays it is postulated that the additional interaction sites afforded by hydrogen bonding might contribute to the enantioseparation [4,10]. The difference between the success or failure of an enantioseparation might also arise from the nature of the buffer and the lipophilic or hydrophilic [11] character of the ions. This paper reports a study of the role of residual silanol groups on a chirally modified zeolite surface.…”

Determination of D-Malate Using Immobilized D-Malate Dehydrogenase in a Flow System and its Application to Analyze the D-Malate Content of Beverages

“…1) The race-mate of malic acid can be produced chemically, so if malic acid is used as an acidulant, the beverage may contain D-malic acid as well as L-malic acid. The separation of D-and L-malic acid has been carried out by high performance liquid chromatography (HPLC) [2][3][4][5][6] and was applied to determine enantiomers in fruits juices. 4) We have utilized the flow systems containing immobilized enzyme for the determination of components of foods.…”