title: Enantiomeric separation of amino acids using micellar electrokinetic chromatography after pre-column derivatization with the chiral reagent 1-(9-fluorenyl)-ethyl chloroformate.
abstract: Direct enantiomeric separations of some racemic amino acids derivatized with 9-fluorenylmethyl chloroformate were obtained using cyclodextrin-modified micellar electrokinetic chromatography (CD/MEKC) with a buffer made up of 5 mM sodium borate (pH 9.2), 150 mM sodium dodecyl sulfate (SDS) and 40 mM gamma-CD. Alternatively, enantiomeric separations were also achieved indirectly using MEKC after pre-column derivatization with (+)-1-(9-fluorenyl) ethyl chloroformate (FLEC). Using either a 10 mM sodium phosphate (pH 6.8) or a 5 mM sodium borate buffer (pH 9.2), each of which contained 25 mM SDS and 10-15% of acetonitrile, FLEC-derivatized serine, alanine, valine, methionine, leucine, phenylalanine, tryptophan, and their diastereomeric pairs were all separated: the L-isomers migrated faster than the corresponding D-isomers. However, when (-)-FLEC was used for derivatization, the D-isomers migrated faster than the corresponding L-isomers. Also, the diastereomers of aspartic acid, glutamic acid, and proline were resolved using a 10 mM sodium citrate buffer (pH 4.4). Using KrF (248 nm) laser-induced fluorescence, the detection limit of (+)-FLEC derivatized DL-amino acids was obtained at the nM level, which was about 100 x more sensitive than UV absorption at 200 nm. Analyte concentrations as low as 3 x 10(-8) M (DL-Val) could be derivatized with (+)-FLEC.
authors.affiliation: Program Resources, Inc/DynCorp, NCI-Frederick Cancer Research and Development Center, MD 21702, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Chan
authors.forename: G M
authors.initials: GM
authors.lastname: Muschik
authors.forename: H J
authors.initials: HJ
authors.lastname: Issaq
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D000596:Amino Acids / Q000032:analysis*; D002845:Chromatography / Q000379:methods*; D005449:Fluorenes / Q000737:chemistry*; D005453:Fluorescence; D007202:Indicators and Reagents / Q000737:chemistry*; D007834:Lasers; D015394:Molecular Structure; D013237:Stereoisomerism; D014466:Ultraviolet Rays
chemical_list: D000097:Acetonitriles; D000596:Amino Acids; D005449:Fluorenes; D007202:Indicators and Reagents; C052812:1-(9-fluorenyl)ethyl chloroformate; C054007:1-(9-fluorenyl)methyl chloroformate; C032159:acetonitrile