Micellar electrokinetic capillary chromatographic method for the separation and quantitation of multiple amino acids as naphthoxy derivatives in pharmaceutical formulations.

The MEKC method is described for the quantitative analysis of 17 amino acids (AA) in pharmaceutical products. The method is based on simply derivatizing the AA with (2-naphthoxy)acetyl chloride under mild conditions. The resulting derivatives were separated by MEKC with borate buffer (35 mM; pH 9.50) including 150 mM SDS at the applied voltage of 25 kV in an uncoated capillary (effective length, 40 cm) and monitored by UV at 230 nm. The detection limits of the amino acid derivatives were in the range of 3.0-8.0 microM (S/N = 3, injection 5.0 s, 6 895 Pa). The precision (RSD) and accuracy (relative error) of the method for intra- and interday analyses of the analytes are all below 5.2%. The amino acid derivatives are stable at room temperature for 33 h studied and the molar absorptivity of the alanine derivative (used as a model) is stable over a wide pH range of 3.00-12.00. This is favorable for monitoring the derivatives in various pH by CE or LC. Application of the method to the analysis of multiple AA in a liquid injection formulation proved satisfactory.