Comparison of the performance of butanol and pentanol as modifiers in the micellar chromatographic determination of some phenethylamines

A procedure was developed for the determination of several phenethylamines (amphetamine, arterenol, ephedrine, phenylephrine, phenylpropanolamine, mep hentermine, methoxyphenamine, pseudoephedrine and tyramine), using micellar mobile phases of sodium dodecyl sulfate (SDS), a C-18 column and UV detect ion. The drugs were eluted at short retention times with conventional aceto nitrile-water or methanol-water mobile phases. In contrast, in the micellar system, they were strongly retained due to association with the surfactant adsorbed on the stationary phase, and needed the addition of butanol or pe ntanol to be eluted from the column. These modifiers allowed a simple way o f controlling the retention. The chromatographic efficiencies obtained with the hybrid mobile phases of SDS-butanol and SDS-pentanol were also very hi gh, mostly in the N=3000-7000 range, significantly greater than those achie ved with a conventional acetonitrile-methanol-water mobile phase. Butanol a nd pentanol yielded similar selectivities, but the latter modifier permitte d significantly shorter retention times than butanol, and was preferred to expedite the analysis of the pharmaceuticals. Most binary combinations of t he nine phenethylamines can be resolved with these mobile phases. A mobile phase of 0.15 M SDS-5% pentanol was used to assay five of the phenethylamin es (amphetamine, ephedrine, phenylephrine, phenylpropanolamine and pseudoep hedrine) in 22 pharmaceutical preparations, which contained diverse accompa nying compounds. The results agreed with the declared compositions and with those obtained with a mobile phase of methanol-acetonitrile-0.05 M phospha te buffer (pH 3) 10:5:85, with no interferences and relative errors usually below 2%. However, with the aqueous-organic mobile phase, the retention ti me for phenylephrine was too low and could not be usually evaluated. (C) 20 00 Elsevier Science B.V. All rights reserved.