Development and Validation of an HPLC Method for the assay of Formoterol Using Electrochemical Detection System

A novel High performance liquid chromatography (HPLC) method for analysis of formoterol in dry powder inhaler has been developed and validated. A formulation containing formoterol and a carrier lactose with a target concentration of formoterol blend 0.266 % w/w was prepared and filled in an Airmax NB7/2 inhaler followed by pharmaceutical performance testing and analysed by HPLC with electrochemical detection. The validationand pharmaceutical performance testing was performed by FDA and ICH regulations for the validation of pharmaceutical samples. The samples were injected onto a reverse phase waters symmetry column maintained at 30 ⁰ C. The mobile phase consisted of potassium di-hydrogen orthophosphate buffer: acetonitrile (79:21, V/V) and the formoterol peak was detected at the following detector settings on the Decade digital electrochemical detector (ECD). Detector settings: working electrode potential (Eox): 0.65 V, Guard cell potential ( E twin ) : 0.70 V. Range select: nano amps, Range: 50 nano amps, Offset: 20%, Filter: 0.1 seconds. The mean blend strength was 0.269 % w/w. Recovery 101.1% and the blend homogeneity (RSD) / % was 0.9. The uniformity of the delivered dose for 6 µg product was DPA/µg: 5.6 ±0.5 and for 12 µg product was DPA/µg : 11.3 ± 08. The fine particle dose for 6 µg product was FPD/µg: 2.4 ± 0.1 and for 12 µg product was FPD/µg: 4.7 ± 0.2. The calibration curve was linear ( r2= 0.9968) over formoterol concentrations ranging from 0.1 to 0.7 µg/ml (n=7). Intra and inter day relative standard deviation (RSD) of variation between 0.3 and 4.1 and accuracy percentage recovery was between 92-108 %. Formoterol was stable over 3 day’s precision. Limit of quantification was 0.1 µg/ml and the limit of detection was 0.0625 µg/ml. The method is selective, reproducible and even though the linearity range is 0.1 µg/ml to 0.7 µg/ml the method has the capacity to be used for determination of formoterol in dry powder inhaler.