Pioglitazone hydrochloride (PGH) can effectively reduce resistance of cells to insulin, and is a widely used treatment for type 2 diabetes. In this study, we discovered that PGH in acidic media could rapidly induce aggregation of gold nanoparticles (AuNPs) to bring about red-to-purple color change caused by electrostatic adsorption and intermolecular hydrogen bonding. Thus, based on this principle, an automatic method with asynchronous-alternating merging-zone was established to determine the PGH content in medicines. Our method involved the calculation of the absorbance ratio and spectrum scanning for two wavelengths. In particular, the proposed method could solve problems of unmanageable aggregation degree, large manual error, and high testing cost in common AuNPs colorimetry. The approach was rapid in sample throughput (a sample/min) under the premise of consumption of 30 μL reagents (8 nmol L−1 AuNPs) per time, high repeatability (RSD ≤ 1.1%, n = 11) and good addition recovery (99–104%) in 0.5–15 mg L−1 range, which is suitable for analyzing PGH content in diabetic medicines.
