Determination of 5-hydroxytryptamine (serotonin) and related indoles by flow injection analysis with acidic potassium permanganate chemiluminescence detection

A simple, rapid and sensitive method for the determination of 5-hydroxytryptamine (serotonin), 5-hydroxytryptophan or 5-hydroxyindole-3-acetic acid, using flow injection analysis with acidic potassium permanganate chemiluminescence detection, is described. The log–log plots for 5-hydroxytryptamine, 5-hydroxytryptophan and 5-hydroxyindole-3-acetic acid gave equations of best fit, of y=−0.03x2+0.51x+6.15 (r2=0.9990), y=−0.05x2+0.35x+5.70 (r2=0.9995) and y=−0.04x2+0.49x+5.60 (r2=0.9999) respectively, where y is log (chemiluminescence emission response (mV)) and x is log (concentration (M)). The log–log calibration functions for the three analytes approximated linearity in the concentration range from 1×10−8 to 1×10−6 M, where the slopes of the log–log plots were within the range from 1.01 to 1.04. The precision (measured as relative standard deviation) for 5-hydroxytryptamine was 2.3% (n=6 at 1×10−7 M). The detection limits (signal-to-noise ratio=3) were 2×10−9 M, 3×10−9 M and 1.5×10−8 M for 5-hydroxytryptamine, 5-hydroxytryptophan and 5-hydroxyindole-3-acetic acid, respectively. Preliminary experiments using an extended range photomultiplier tube realised enhanced detection limits due to the wavelength of maximum emission being centered around 670 nm rather than 610 nm as previously thought.