Octopamine and synephrine are endogenous biogenic, and hydrophilic, amines. Both compounds are used as an alternative to ephedrine. Synephrine is also used as a fat loss drug. Both compounds are very similar in nature. Analytical HPLC method based on a mixed-mode HPLC approach, using a Primesep 200 column was developed to separate octopamine and synephrine with LC/MS compatible conditions. Octopamine and synephrine are retained by combination of reversed-phase and cation-exchange mechanisms. Method can be used for analysis of both substances in biological fluids (blood, serum, urine). Monitoring can be done by UV, LC/MS, ELSD, CAD, etc.