Chromatographic analysis of phenethylamine-antihistamine combinations using C-8, C-18 or cyano columns and micellar sodium dodecyl sulfate-pentanol mixtures

The chromatographic behaviour of binary and ternary mixtures of several phe nethylamines (phenylephrine, phenylpropanolamine, ephedrine, pseudoephedrin e and methoxyphenamine) and antihistamines (pheniramine, carbinoxamine, dox ylamine, chlorpheniramine, dexchlorpheniramine, dexbrompheniramine, diphenh ydramine, tripolidine, azatadine and phenyltoloxamine), found in cough-cold pharmaceutical preparations, was studied using C-8, C-18 and cyano columns , micellar mobile phases of sodium dodecyl sulfate (SDS) and pentanol and U V detection. Using a C-8 column and mobile phases of 0.05 mol 1(-1) SDS-6% v/v pentanol or 0.15 mol 1(-1) SDS-2% v/v pentanol at pH 7, more than 30 di fferent phenethylamine-antihistamine combinations can be resolved in <15 mi n. Intra- and inter-day repeatabilities and reproducibilities evaluated at three different drug concentrations (0.5, 5 and 25 <mu>g ml(-1), n = 10) we re below 1.6, 2.5 and 2.4%, respectively. The drug amounts found in 18 form ulations agreed with those declared by the manufacturers within the toleran ce limits, and with those obtained using a mobile phase of 55% v/v methanol at pH 7. No interference was observed from other accompanying drugs such a s acetylsalicylic acid, ascorbic acid, betamethasone, bromhexine, caffeine, codeine, dextromethorphan, paracetamol, prednisolone, salicylamide and tar trazine. The proposed procedure has the advantage over the conventional aqu eous-organic procedure of using a small amount of organic solvent, which is highly retained in the SDS solution. The efficiencies an also greater. On the other hand, in the micellar system, the retentions of phenethylamines a nd antihistamines are similar, although the compounds can be easily resolve d. In contrast, using the methanol-water mobile phase, the phenethylamines are weakly retained, whereas the antihistamines usually show a high retenti on.