Simultaneous Determination of Pyrroloquinoline Quinone Redox Species via a Dual-Mode High-Performance Liquid...

Pyrroloquinoline quinone (PQQ) is a redox-active cofactor that exists in the oxidized and reduced forms, with the reduced species being particularly significant for biological activity. However, accurate quantification of the reduced form in complex matrices remains technically challenging due to its instability, low solubility, and high susceptibility to atmospheric oxidation. A robust and versatile high-performance liquid chromatography method featuring two complementary analytical modes was established in this study to overcome these limitations. The "Native mode" uses a strongly acidic eluent to suppress oxidation during analysis, enabling simultaneous quantification of both redox forms and determination of their native distribution. Conversely, the "Total mode" measures the total PQQ after pretreatment with ascorbic acid and γ-cyclodextrin, which converts PQQ species to a stabilized reduced form and improves solubility. Method validation demonstrated excellent linearity (R² = 0.9996), low detection limits (limit of detection: 0.20 mg/L; limit of quantification: 0.50 mg/L), and high precision (relative standard deviation <3%). The method also achieved recoveries of 99-101% in commercial beverages and enabled detection of biologically generated reduced PQQ in yeast culture. This dual-mode, redox-specific approach provides a reliable tool for industrial quality control and offers a useful platform for investigating PQQ redox dynamics in complex systems.