Biomedical applications of amino acid detection by capillary electrophoresis

CE-MS for the Analysis of Amino Acids

Amino acids play an important role in clinical analysis. Capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) has proven to possess several characteristics that make it a powerful and useful tool for the analysis of amino acids in clinical studies. Here we present a method for the separation and quantitative analysis of 27 amino acids in urine based on CE-ESI-MS. The method presents an improved resolution between the isomers Leu, Ile, and aIle, in comparison to other CE-ESI-MS methods in the literature. This method is fast, selective, and simple and has improved sensitivity by applying a pH-mediated stacking strategy, showing that it can be successfully used for amino acid analysis and probably for other small cationic metabolites.

Development and validation of a CE-MS method for the targeted assessment of amino acids in urine

A CE-ESI-MS method was developed and validated for the separation and quantitative analysis of amino acids (AA) in urine. Experimental parameters related to the CE-MS interface, BGE, and mass spectrometer (MS) settings were optimized providing a good separation of 27 AA, including the isomers L-leucine, L-isoleucine, and L-alloisoleucine, in less than 30 min. The sheath liquid was composed by 0.50% formic acid in 60% (v,v) methanol-water delivered at a flow rate of 5 μL/min. The BGE consisted of 0.80 mol/L formic acid at pH 1.96 and 15% methanol. A pH stacking procedure was implemented to enhance sensitivity (a 12.5% NH4 OH solution was injected at 0.5 psi/9 s prior to samples injected at 0.6 psi/20 s). The proposed method was validated according to FDA and ICH protocols exhibiting acceptable parameters. Analytical curves presented coefficients of determination from 0.996 to 0.9997 (with large F statistics and low p-values). LODs and quantification ranged from 0.63 to 29 μmol/L and from 1.9 to 86 μmol/L, respectively. Practical repeatability was obtained for all AA with coefficients of variation better than 0.55% CV (migration time) and 1.7% CV (peak area ratios; methionine sulfone as internal standard). Recoveries of AA in spiked urine ranged from 92.0 to 123% with few exceptions. Moreover, a successful quantification of AA in pooled control and test urine samples, which compose a vesicoureteral reflux cohort, was achieved showing the potential applicability of the proposed method for targeted metabolomics studies using CE-ESI-MS with an Ion Trap as mass analyzer.