Reaction rate, activation energy, and detection limit for the reaction of 5-furoylquinoline-3-carboxaldehyde with neurotransmitters in artificial cerebrospinal fluid

The fluorogenic reagent 5-furoylquinoline-3-carboxaldehyde (FQ) has proven valuable in the analysis of proteins and small neurotransmitters. We monitored the reaction rate between this reagent and five neurotransmitters at 40° and 65°C in artificial cerebrospinal fluid. The reactions followed pseudo-first order kinetics. The activation energy for the reaction of FQ was 10.6, 10.7, 22.0, 31.4, and 34.4 kJ mol−1 for alanine, taurine, γ-aminobutyric acid (GABA), glutamine, and glutamic acid, respectively. At 65°C, the reaction rate was quite similar for alanine, taurine, glutamine, and glutamic acid (1.8×10−3 s−1) but was twice as fast for GABA. A reaction time of nearly 1 h was required to quantitatively convert these neurotransmitters to their fluorescent products at 65°C. Detection limits for the labeled neurotransmitters were 10−9–10−8 M, which corresponded to 0.3–7 amol injected onto the capillary.