Validation of a reverse-phase high performance liquid chromatographic method for concurrent assay of a weak base (salmeterol xinafoate) and a pharmacologically active steroid (fluticasone propionate)

The analysis of weakly basic drugs such as salmeterol xinafoate (SX) by reverse-phase liquid chromatography remains a problem, particularly when present in combination with other drugs such as steroids and weak acids. This study describes the validation of an assay for a weakly basic drug, salmeterol (SB), its weakly acidic counter-ion, 1-hydroxy-2-naphthoic acid (XA), and the neutral glucocorticoid, fluticasone propionate (FP) using a second-generation silica stationary phase (Inertsil ODS-2). The assay utilized an Inertsil ODS-2 base-deactivated 250 mm × 4.6 mm, 5 μm HPLC column, with 75:25 methanol:0.6% aqueous ammonium acetate as the mobile phase. Under these near neutral conditions, SB demonstrated a good peak shape (tailing factor = 1.21 ± 0.02, n = 85). The method provided a short analysis time: XA, tR = 2.96 min; SB, tR = 5.23 min and FP, tR = 7.01 min. The assay displayed good sensitivity for both XA (LOD for SX = 0.22 μg mL−1) and SB (LOD for SX = 0.26 μg mL−1). The limit of detection for FP was 0.19 μg mL−1. Neither of the drugs was found to interfere in the determination of the other and the assay accuracy (% recovery) was high (the recoveries were: 99.58 ± 1.85% for XA, 99.49 ± 1.88% for SB and 100.24 ± 1.28% for FP). The assay reproducibility was determined with a mean coefficient of variance for the five calibration concentrations of XA = 0.71 ± 0.18%; SB = 1.11 ± 0.64% and FP = 0.92 ± 0.14%. Analysis of a pressurized metered dose inhaler formulation demonstrated recovery of the analytes that are within pharmacopoeial limits. It was shown that RP-HPLC was suitable for the high throughput analysis of the combination of SX and FP.