Spectrophotometric determination of total serotonin derivatives in the safflower seeds with Ehrlich’s reagent and the underlying color reaction mechanism

A new spectrophotometric method for the determination of total serotonin derivatives in the safflower (Carthamus tinctorius L.) seeds is described. The determination is based upon a color reaction between serotonin derivatives and p-dimethylaminobenzaldehyde (Ehrlich’s reagent), which follows the electrophilic substitution reaction mechanism at the indole ring. The main factors affecting correct measurement of total serotonin derivatives concentration were studied. The maximum absorption wavelength of the complex was determined at 625 nm. Lambert-Beer’s law is obeyed in the concentration range of 0.025–0.5 mmol/l, with a correlation coefficient (R2) of 0.9996, a recovery of 99.7%, and a relative standard derivation (RSD) of 1.5%, respectively. The proposed method presented satisfactory results in the determination of total serotonin derivatives in the extract from a strain of safflower seeds, and thus is recommended as a routine method for total serotonin derivatives quantitation.