Cation-exchange/hydrophilic interaction mixed-mode liquid chromatographic method for analyzing the trigonelline class of bioactives in coffee beans

The coffee phytochemical trigonelline and its roasting products nicotinic acid and N -methylpyridinium represent an important class of bioactives that mediate the health benefits of coffee consumption. However, there is a paucity of methods for their simultaneous analysis in coffee beans, especially those affordable and reliable for widespread routine use. To improve this situation, an easy-to-use HPLC−UV method was developed in this study based on a reversed-phase/cation-exchange mixed-mode column showing unique chromatographic selectivity toward the polar and ionic analytes over the matrix components of coffee. The selectivity was achieved by using a decreasing acetonitrile gradient, which tuned the column to a cation-exchange/hydrophilic interaction (CEX/HILIC) mixed separation mode whilst minimizing its hydrophobic interaction capability. The method was assessed for figures of merit, giving limits of detection in coffee beans at around the 0.1 mg/100 g wet matter level, and verified for its applicability to a heterogeneous set of coffee bean samples differing in roasting degree and origin.