Capillary Electrophoretic Separation and Quantification of Tryptophan and Tyrosine Enantiomers in Nutritional Supplements Using Sulfated‐β‐Cyclodextrin

Enantioselective analysis of two aromatic amino acids, namely, tryptophan (TRP) and tyrosine (TYR), was investigated by incorporating sulfated‐β‐cyclodextrin as the enantioselective agent. Performance of chiral separation was studied using background electrolyte (BGE) pH, applied voltage, capillary temperature, and the time of sample injection, which were all thoroughly optimized. Optimum separation conditions were established using a 25 mM BGE at pH 2.25 with 1.125 mM S‐β‐CD. Capillary operating temperature was 25°C, operating voltage was 22 kV, and samples’ introduction time was 7 s with UV detection at λ = 214 nm. The analytical properties of the chiral method were determined. Linearity, LOD and LOQ, precision, and accuracy were assessed for the identification of TRP and TYR chiral isomers present in commercial dietary supplements. The LODs were estimated to be 11.05 and 12.02 μ g/mL for L‐TRP and D‐TRP optical isomers and 23.12 and 23.93 μ g/mL for L‐TYR and D‐TYR optical active isomers. The LOQs were determined to be 24.07 and 24.79 μ g/mL for L‐TRP and D‐TRP optical active isomers and 47.81 and 48.02 μ g/mL for L‐TYR and D‐TYR optical active isomers. Ultimately, the technique was utilized for the analysis of L‐TRP and L‐TYR in dietary supplements, and the quality of these supplements was validated by identifying the absence of the enantiomeric impurities in both samples.