A Self‐Assembly Pipette Tip Restricted Access Mesoporous Polypyrrole Solid‐Phase Extraction Coupled With Capillary Electrophoresis With Diode Array Detection for the Determination of Enalapril in Urine Samples

A miniaturized self-assembly pipette tip with restricted access mesoporous polypyrrole solid-phase extraction, combined with capillary electrophoresis with diode array detection (CE-DAD), was developed to rapidly extract and determine enalapril from urine samples. The CE-DAD technique used 50 mmol L^-1 phosphate (pH 7) as the background electrolyte, a voltage of 13 kV, a 30 mbar hydrodynamic injection for 4 s, a capillary temperature of 25°C, and a wavelength of 195 nm to achieve a migration time of 6.3 min with satisfactory peak asymmetry and no interfering and/or baseline noise. The factors that influenced the extraction efficiency were evaluated and optimized: 750 µL sample at pH 7.5, 40 mg adsorbent, 250 µL hexane as a washing solvent, and 750 µL acetonitrile as eluent, resulting in recoveries around 74%. Linearity was acceptable in the 100-3000 ng mL^-1 range, and the selectivity and accuracy were also suitable. The limits of detection and quantitation were 30 and 50 ng mL^-1, respectively. The adsorbent effectively removed 87% of the proteins and may be reused three times. The analytical approach was successfully verified and used to analyze enalapril in urine samples collected from volunteers. Finally, the greenness of the researched technique was assessed using five measures that showed good eco-friendliness.