Chiral capillary electrophoretic separation of amino acids derivatized with 9‐fluorenylmethylchloroformate using mixed chiral selectors of β‐cyclodextrin and sodium taurodeoxycholate

Abstract

Chiral separation of 19 pairs of amino acid (AA) enantiomers derivatized with 9-fluorenylmethylchloroformate (FMOC) was successfully conducted by capillary electrophoresis using the mixture of beta-CD and sodium taurodeoxycholate (STDC) as selectors. Resolution was considerably superior to that obtained by using either beta-CD or STDC alone. After a systematic inspection, a buffer composed of 150 mM borate and 18% v/v isopropanol at pH 8.0, dissolved with 30 mM beta-CD and 30 mM STDC, was adopted and able to generate baseline resolution (>1.50) for 17 pairs of FMOC-AA enantiomers and somewhat lower resolution for arginine (1.36) and alanine (1.18), respectively. Experimental data revealed that the addition of the second selector did not increase the mobility difference between a pair of enantiomers (Delta mu = mu(D) - mu(L) and the number of theoretical plates (N), but decreased the summed apparent mobility of a pair of enantiomers (Sigma mu = mu(D) - mu(L)), which was mainly due to the decrease of the electroosmotic flow. The variation of Sigma mu was thus the major reason responsible for the improvement of chiral resolution in this study. The result demonstrated that not only the intrinsic selectivity of the selectors was the basis of the chiral separation, but also the non-chiral effect of the selectors, the change of the electroosmotic flow, was an important factor in enhancing the enantioseparation resolution. This study could probably help to explain the reasons for resolution improvement in some dual selectors systems, which are not very clear at present.

Amino acids: Aspects of impurity profiling by means of CE

“…However, in many cases derivatization is employed in order to increase the sensitivity of the method. Among others, dansyl chloride [43], FMOC [44,45], and 2-(9-anthryl)ethyl chloroformate [46] have been proven to be suitable labeling reagents.…”

Recent advances in amino acid analysis by CE

“…A mixture of b-CD and sodium taurodeoxycholate (STDC) was also used to obtain better resolution than using either b-CD or STDC alone to separate 19 FMOC-labeled AAs (Table 1) [54]. Seventeen pairs of FMOC-AA enantiomers were resolved with resolution of 1.5 (only Arg (1.36) and Ala (1.18) have lower resolution).…”

Cyclodextrins in capillary electrophoresis enantioseparations – Recent developments and applications

“…Further studies in the last few years reported the evaluation of derivatized amino acids in CD-mediated MEKC. b-CD or c-CD was used in combination with taurocholic acid [183] or a dual surfactant system consisting of SDS and taurocholic acid [184]. The analysis of FITC-labeled amino acids in microalgae was performed by CD-MEKC-LIF using a BGE consisting of 30 mM SDS and 20 mM b-CD in a 100 mM sodium borate, pH 9.7 [185].…”