Green HPTLC and stability-indicating RP-HPLC for the assay of dextromethorphan hydrobromide and menthol in their lozenges

Abstract

Two chromatographic methods were developed for the assay of the FDA approved lozenges containing dextromethorphan hydrobromide (DXT) and menthol (MNT). The first was a green HPTLC method which uses a mobile phase of methanol-ammonia (10:0.1, v/v). The densitometric measurements of the spots which were retained at 0.28±0.01 for DXT and 0.76±0.02 for MNT was done at 210nm. The other method was RP-HPLC method with stability indicating merits at which a mixture of 20mM phosphate buffer pH 3 and acetonitrile as mobile phase in isocratic mode was used. The cited drugs were resolved in RP-HPLC method using isocratic elution using 20mM phosphate buffer: acetonitrile (65:35 v/v) with retention times of 2.21 and 3.47min for MNT and DXT, respectively and quantified using 215nm. Both methods were entirely validated and both methods were successfully able to analyze both drugs in presence of lozenges inactive ingredients. HPLC method had the advantage of being stability indicating at which resolution of the drugs from their forced degradation products was successfully attained. For HPTLC method, both drugs showed reasonable RF values when compared to rapidly eluted MNT in RP-HPLC; also it was more environmentally friendly than RP-HPLC as it used solvents which are less toxic and greener.