The chromatographic behaviour of some active ingredients in
cough-cold pharmaceutical preparations, the
antihistamine chlorpheniramine (or the dextro enantiomer
dexchlorpheniramine), and the
phenethylamines phenylephrine,
phenylpropanolamine and
pseudoephedrine, has been studied using a C(18) column, micellar mobile phases of
sodium dodecyl sulphate (SDS) and pentanol, and with UV detection. All possible combinations of
chlorpheniramine/
phenethylamine were resolved and determined using a mobile phase of 0.15 M SDS-6% (v/v) pentanol at pH 7, with analysis time below 7 min. Repeatabilities and within laboratory precisions were evaluated at four different
drug concentrations in the range 0.5-25 mug ml(-1) (n=5), resulting RSDs below 1.6%. The
drug amounts found in the analysis of 14 commercialised preparations agreed with those declared by the manufacturers within the tolerance limits, and with those obtained using an aqueous 60% (v/v)
methanol reference mobile phase. No interference was observed from other accompanying drugs such as
acetylsalicylic acid,
ascorbic acid,
betamethasone,
caffeine,
codeine phosphate,
diphenhydramine,
lactose,
paracetamol, and
prednisolone. The studied combinations required a rather high amount of
methanol in conventional RPLC to be eluted from the column. In contrast, the proposed procedure used a much lower amount of organic
solvent (pentanol), which is highly retained in the SDS
solution, being also less toxic than
methanol.