Enantioseparation of N-derivatized amino acids by micro-liquid chromatography/laser induced fluorescence detection using quinidine-based monolithic columns☆

Abstract A novel carbamoylated quinidine based monolith, namely poly( O -9-[2-(methacryloyloxy)-ethylcarbamoyl]-10,11-dihydroquinidine- co -ethylene dimethacrylate (poly(MQD- co -EDMA)), was prepared for the micro-LC enantioseparation of N -derivatized amino acids. The influence of the mobile phase composition, including the organic modifier proportion, the apparent pH and the buffer concentration, on the enantioresolution of N -derivatized amino acids was systematically investigated. Satisfactory column performance in terms of permeability, efficiency and reproducibility was obtained in most cases. The majority of the enantiomers of the tested N -protected amino acids, including 3,5-DNB, 3,5-DClB, FMOC, 3,5-DMB, p -NB, m -ClB, p -ClB and B derivatives, could be baseline separated on the poly(MQD- co -EDMA) monolithic column within 25 min. A self-assembled laser induced fluorescence (LIF) detector was employed to improve sensitivity when analyzing 7-nitro-2,1,3-benzoxadiazole (NBD) derivatives of amino acids. Ten NBD-derivatized amino acids, including arginine and histidine whose enantioseparation on quinidine carbamate based CSPs has not been reported so far, were enantioresolved on the poly(MQD- co -EDMA) monolith column. It is worth noting that the d -enantiomers of NBD-derivatized amino acids eluted first, except in the case of glutamic acid. The LOD values obtained with the LIF detector were comparable to those reported using conventional LC-FL methods. The prepared poly(MQD- co -EDMA) monolithic column coupled with the LIF detector opens up interesting perspectives to the determination of trace d -amino acids in biological samples.