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Technical Note

Retention of Salbutamol Using Various C18 Phases

Introduction

Salbutamol (also known as albuterol) is a bronchodilating agent which is ubiquitously used in the treatment of asthma and chronic obstructive pulmonary disorder (COPD). It is a polar hydrophilic compound (see Figure 1) which can be problematic when analyzing using reverse phase HPLC. Polar compounds can elute very close to the solvent front. It is therefore ideal for an eluting compound to have a capacity factor (k) between 1 and 10. Polar compounds with poor retention can have k values close to zero. Analyses with this level of retention are not reproducible and so it is important to increase the affinity that polar compounds have for the stationary phase. The technical note investigates the impact on retention of salbutamol by changing the chemistry of the stationary phase. When analyzing salbutamol in accordance with the British Pharmacopeia, the monograph stipulates the use of 'end-capped octadecylsilyl silica gel for chromatography (5 µm)'. This definition does not specify the type of end capping giving scope to the evaluation of different stationary phase whilst still adhering to BP requirements. Salbutamol sulfate was analyzed according to the British Pharmacopeia monograph: Salbutamol Pressurised Inhalation, Suspension. This analysis was performed on four Quasar columns: C18, AQ, AQ Plus and SPP C18/PFP in order to obtain the maximum improvement in the retention of salbutamol.