Simultaneous determination of 11 nootropic substances potentially adulterated in dietary supplements for improving...

Recently, the demand for improved brain function and concentration has increased in the dietary supplement market. However, to artificially enhance their pharmacological efficacy, dietary supplements may be illegally adulterated with unauthorised substances. Therefore, we developed a rapid and accurate method to simultaneously determine 11 nootropic substances using an ultra-high-performance liquid chromatography (UPLC) system equipped with a photodiode array (PDA) detector. In addition, sample preparation procedures were semi-optimised for various types of matrices, including solid (hard capsule, tablet, powder, and pill) and liquid (oil and extract) samples. The method was validated to determine the limit of detection (LOD), limit of quantification (LOQ), method detection limit (MDL), method quantitation limit (MQL), specificity, linearity, precision, accuracy, recovery, stability, and matrix effects. The validation results satisfied international validation guideline requirements. To test the applicability of the method, 55 real samples advertised as effective brain health, memory, and cognition supplements were analysed. Among the real samples, vinpocetine (2.483 and 7.296 µg/g), and kavain (69-44.056 µg/g) were detected. In addition, the detected compounds were confirmed by comparing their fragmentation patterns with those of the reference standards using liquid chromatography-quadrupole-time-of-flight mass spectrometry (LC-QTOF/MS). In conclusion, the UPLC-PDA method not only rapidly and accurately quantifies illegal nootropics but also enables the pre-emptive investigation and identification of 11 nootropic substances in illegal dietary supplements to protect public health.