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An online dynamic p H junction preconcentration method was developed for quantification of 5-aminolevulinic acid (ALA) by CE with the separation time less than 6 min. The optimal dynamic p H junction of ALA was carried out between p H 9.3 borate buffer (BGE, 40 mM) and p H 2.5 phosphate buffer (sample matrix, 40 mM) when 4.1 cm of sample plug was hydrodynamically injected into an uncoated fused-silica capillary (48.5 cm in length, id of 50 μm). If a 24 kV separation voltage was applied, the calibration curve of ALA peak area (200 nm) showed good linearity ( R2 = 0.9991) ranging from 0.01 to 6.5 mg/mL. The reproducibility of this system was excellent with RSDs ( n = 10) of 2.5% for peak area response and 0.6% for migration time at ALA concentration of 0.5 mg/mL. The LOD was evaluated as 1.0 μg/mL ( S/ N > 3). Compared to conventional CE procedure, the sensitivity was successfully improved over 50-fold. The analytical results of pharmaceutical formulations show a good agreement with those by HPLC ( r = 0.94). [ABSTRACT FROM AUTHOR]