A rapid, sensitive, and solvent-free normal-stacking micellar electrokinetic chromatog. method for measuring morphine sulfate and morphine-6-glucuronide in human serum using codeine phosphate as an internal standard has been developed.The integration of in-capillary derivatization and fluorescence detection for minimizing operator and environmental concerns was employed.For peak intensification and sharpness, the normal-stacking mode was utilized, wherein the capillary was pre-filled with a water plug for four seconds prior to sample loading.Upon injection of serum samples into capillary via hydrodynamic mode for 20 s and application of a separation voltage of 10 kV (21 ± 1°C), the low ionic strength within the water plug area facilitates the movement of analyte ions being tested, allowing them to reach the background electrolyte containing 75 mM disodium tetraborate decahydrate (pH 10.5), 0.35 mM potassium ferricyanide, and 80 mM sodium dodecyl sulfate.At the boundary between the water plug zone and background electrolyte, sharply intensified zones were achieved.Morphine sulfate, morphine-6-glucuronide and codeine phosphate were then oxidized into highly fluorescent pseudo-derivatives while traveling through the capillary.The mean recoveries of morphine sulfate and morphine-6-glucuronide ranged from 88.21 to 97.54 and 87.62 to 97.12%, resp.After a single oral dose of a controlled-released morphine sulfate tablet, the proposed method effectively measured the tested analyte and its metabolite, morphine-6-glucuronide in clin. human specimens.The environmental sustainability of the method is evaluated through the Green Anal. Procedure Index and the anal. greenness metric for sample preparation, while the Blue Applicability Grade Index is utilized to assess its practicality.