Effect of alkali metal hydroxides on the enantioseparation of amines using di-O-isopropylidene-keto-L-gulonic acid as the selector in NACE.
The present work demonstrates the importance of the ionic composition in the BGE for enantioseparation. (-)-2,3:4,6-di-O-Isopropylidene-2-keto-L-gulonic acid ((-)-DIKGA) has been used as the chiral selector in methanolic and ethanolic BGEs. The influence of added alkali metal hydroxides on the EOF and the chiral separation of amines (atenolol, isoprenaline, pindolol and propranolol) have been studied. The ion-pair formation constants in ethanol were determined by precision conductometry for the enantiomers of pindolol with (-)-DIKGA, for Li(+), Na(+) and Cs(+) with (-)-DIKGA, and also for the corresponding alkali metal hydroxides. The effective mobilities and the enantiomeric mobility differences were affected by the type of alkali metal hydroxide (LiOH, NaOH, KOH, RbOH or CsOH) added to the BGE. The effective mobility and mobility difference were increased with decrease in solvated radius of the alkali metal cation. These differences could partly be correlated to the ion-pair formation constants of the alkali metal cations with the chiral selector, affecting the equilibrium concentration of the free selector. The electroosmosis was also affected by the alkali metal hydroxide added to the BGE. The cathodic electroosmosis decreased with decreasing solvated radius of the alkali metal cation added to the BGE. Interestingly, the cathodic EOF was even reversed, i.e. became anodic in the ethanolic BGEs containing KOH, RbOH or CsOH and the methanolic ones with RbOH and CsOH.
Hedeland
Ylva
Y
Department of Analytical Chemistry, Division of Analytical Chemistry, Uppsala University, Uppsala, Sweden. Ylva.Hedeland@farmkemi.uu.se
Haglöf
Jakob
J
Beronius
Per
P
Pettersson
Curt
C
D000588:Amines / Q000737:chemistry / Q000302:isolation & purification*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry*; D053841:Electroosmosis; D019075:Electrophoresis, Capillary / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000737:chemistry*; D007287:Inorganic Chemicals / Q000737:chemistry; D008672:Metals, Alkali / Q000737:chemistry*; D013237:Stereoisomerism; D013400:Sugar Acids / Q000737:chemistry*
C441632:2,3-4,6-di-O-isopropylidene-2-ketogulonic acid; D000588:Amines; D019086:Bridged Bicyclo Compounds, Heterocyclic; D006878:Hydroxides; D007287:Inorganic Chemicals; D008672:Metals, Alkali; D013400:Sugar Acids