Quantification of bambuterol hydrochloride in a formulated product using solid-state NMR

Carbon-13 NMR spectra of the stable polymorphs of solid bambuterol hydrochloride (BHC) and terbutaline sulfate (TBS) are reported and the resonances assigned with the aid of solution-state spectra. A protocol is presented for quantification of BHC in a formulation in lactose, together with TBS, relative to a reference peak from magnesium stearate. This protocol compares the intensity of an aromatic signal of BHC with that of the main-chain methylene carbons of the stearate. It is shown that the limit of detection (LOD) of BHC in this system under the conditions described is 0.5% with an effective limit of quantification (LOQ) of 1.0%. A calibration plot for the quantification is presented and the various factors affecting the accuracy of the measurements are described. No discernible differences are found in the spectra of physical mixtures of the components, whole tablets, and crushed or ground tablets.