In this study, we demonstrated nano-flow injection analysis (nano-FIA) with quadrupole time-of-flight mass spectrometry (Q-TOFMS) for 17 highly polar intermediates produced during glycolysis, the tricarboxylic acid (TCA) cycle, and the pentose phosphate pathway (PPP). We optimized the analytical conditions for nano-flow injection/Q-TOFMS, and set the flow rate and ion source temperature to 1000 nL/min and 150 °C, respectively. Under optimal conditions, a single run was finished within 3 min, and the RSD value of 50 sequential injections was 4.2%. The method also showed quantitativity of four stable-isotope-labeled compounds (r2 > 0.99), demonstrating its robustness, high repeatability, and specificity. In addition, we compared three sample-preparation methods for rodent blood samples and found that protein precipitation with threefold methanol was the most effective. Finally, we applied the method to plasma samples from the serotonin syndrome (SS) model and control rats, the results of which were evaluated by principal component analysis (PCA). The two groups showed clearly separated PCA score plots, suggesting that the method could successfully catch the differences in metabolic profiles between SS and control rats. The results obtained from our new method were further validated by using the established gas chromatography/tandem mass spectrometry method, which demonstrated that there were good correlations between the two methods (R = 0.902 and 0.958 for lactic acid and malic acid, respectively, each at p < 0.001), thus proving the validity of our method. The method described here enables high-throughput analysis of metabolites and will be of use for the rapid analysis of metabolic profiles. Graphical abstract.
Keywords: High-throughput metabolite analysis; Nano-flow injection analysis; Quadrupole time-of-flight mass spectrometry; Serotonin syndrome model.