title: Analysis of the enzymatic racemization of D-aspartic acid to L-aspartic acid by the on-line coupling of a solid-phase extraction column and a ligand-exchange high-performance liquid chromatography column.
abstract: D-Aspartic acid can be enzymatically biotransformed with D-amino acid oxidase and aminotransferase to L-aspartic acid. The reaction was surveyed at three temperatures and a period of 3 days, however, L-aspartic acid can be produced only at the reaction temperature 90 degrees C. However, the separation of D-aspartic acid and L-aspartic acid by ligand-exchange chromatography showed matrix interference. Therefore, the column-switching technique by coupling a solid-phase extraction (SPE) column to the analytical ligand-exchange HPLC column was used to eliminate the matrix effect. The pretreatment of reaction samples with the SPE column was considered as a combination of size-exclusion chromatography and ion-pair chromatography. The ion-pair reagent was 0.005 M sodium 1-octanesulfonate aqueous solution adjusted to pH 2.2. Part of the first eluted peak from the SPE column was then switched through the ligand-exchange column and analyzed with a 0.25 mM Cu2+ aqueous mobile phase of pH 3.6. The quantitative analysis of D- and L-aspartic acids was performed by the standard addition method. Overall, the separation and analysis of D- and L-aspartic acids in the enzymic solution was convenient, fast, and successful with the developed on-line LC-LC column-coupling and column-switching system.
authors.affiliation: Department of Chemistry, Chung Yuan Christian University, Chungli, Taiwan. chengce@cycu.edu.tw
authors.forename: C
authors.initials: C
authors.lastname: Cheng
authors.forename: S C
authors.initials: SC
authors.lastname: Wu
mesh_terms: D001224:Aspartic Acid / Q000737:chemistry*; D002850:Chromatography, Gel / Q000295:instrumentation* / Q000379:methods; D002851:Chromatography, High Pressure Liquid / Q000295:instrumentation* / Q000379:methods; D004798:Enzymes / Q000737:chemistry; D008024:Ligands; D013237:Stereoisomerism
chemical_list: D004798:Enzymes; D008024:Ligands; D001224:Aspartic Acid