A Simple and Affordable CZE–UV Method for Quality Control of Insulin in Active Pharmaceutical Ingredient and Formulations Using Quadruple Polymer‐Coated Capillary

Substandard and falsified medicines pose a significant public health threat, particularly in low-income countries. Ensuring pharmaceutical quality is crucial to mitigate risks associated with ineffective and harmful medications. Among others, developing and implementing robust and cost-effective analytical methods is an important and quick strategy for ensuring the quality of medicines. This study aimed to develop a robust and cost-effective capillary zone electrophoresis method with UV detection for insulin analysis in active pharmaceutical ingredient and formulations. A multilayer capillary coated with polybrene and poly(sodium 4-styrenesulfonate) improved repeatability. The method was optimized by systematically evaluating running buffer composition, pH, ionic strength, and voltage, achieving optimal separation with a 60 mM phosphate buffer at pH 8.0. It demonstrated excellent precision, accuracy, linearity, and robustness. Application of the method to insulin commercial samples verified compliance with pharmacopoeial standards. The method could be a reliable and accessible alternative for quality control of insulin in resource-limited settings, supporting efforts to combat substandard pharmaceuticals and protect public health. Moreover, the method aligns with green chemistry principles, as it eliminates the need for organic solvents, either as solvent or as a component of the running buffer.