Chiral ligand-exchange capillary electrochromatography with thermo-responsive poly(N,N-dimethylacrylamide) as coating for efficient separation of D,L-amino acids.

Herein, for addressing the issue in enantioseparation and being inspired by regulating hydrophobic/hydrophilic interactions in smart polymer through varying external environmental conditions, we demonstrated a chiral ligand exchange-capillary electrochromatography-UV (CLE-CEC-UV) system by introducing a thermo-responsive poly(styrene-maleic anhydride-N,N-dimethylacrylamide) (PSMDMA) to the coating for enantioseparation of dansylated D,L-amino acids (Dns-D,L-AAs). As metal ions-chiral ligands complexes in running buffer played the role of chiral selectors, the proposed CLE-CEC-UV system exhibited significantly enhanced enantioseparation efficiency for the first time, especially, 15-pairs were baseline separated at 40 °C, compared to 4-pairs baseline separated at 20 °C among 16-pairs of Dns-D,L-AAs. It was attributed to the high hydrophobic interactions between Dns-D,L-AAs and PSMDMA coating at high temperature. Additionally, the formation of strong coordinated complexes between metal ions, Dns-D,L-AAs and chiral ligands was also a key to achieve high CLE-CEC-UV performance. The proposed method showed an excellent linear dependence relation between concentration of L-alanine and UV absorbance intensity, ranging from 0.1 to 3.0 mmol L-1, with limit of detection (LOD) of 10.0 μmol L-1. Further evaluation of alanine aminotransferase activity in various mice organs with L-alanine as the substrate confirmed the potential application of the CLE-CEC-UV technique. Moreover, the coated capillary exhibited good repeatability with relative standard deviations less than 1.86 % for migration time and less than 3.94 % for resolution. This work highlights and integrates the advantages of smart polymer coatings and metal ion-chiral ligand complexes, encouraging development of more unique CLE-CEC systems for efficient enantioseparation and practical application in living bio-systems.