Clean-up, detection and determination of salbutamol in human urine and serum

Salbutamol {2-(tert-butylamino)-1-[4-hydroxy-3-(hydroxymethyl)phenyl]ethano l}, also known as albuterol, is clinically the most widely used beta(2)-adr enoceptor agonist in the treatment of bronchial asthma. During this study, we evaluated liquid-liquid extraction (LLE) and solid-phase extraction (SPE ) in order to develop a reliable extraction method followed by analysis usi ng liquid chromatography and gas chromatography. An assay is described whic h involves SPE as the clean-up method followed by gas chromatography-mass s pectrometry to determine salbutamol levels in human serum after oral admini stration. The SPE method requires the use of a hyper-cross-linked styrene-d ivinylbenzene bonded phase (ENV+) without involving any sample pre-treatmen t to obtain 60-65% recoveries for salbutamol and terbutaline as the interna l standard. Distilled water and 1% trifluoroacetic acid in methanol were fo und to be the most suitable washing solvent and eluting solvent, respective ly. A detection limit of 2 ng mL(-1) was achieved by derivatization with N- methyl-N-trimethylsilyltrifluoroacetamide to form trimethylsilyl (TMS)-salb utamol (m/z 369) and TMS-terbutaline (m/z 356). The relationship between th e ratio of the peak area of salbutamol to that of the internal standard and concentration was linear for the range tested (2-200 ng mL(-1)) and the co rrelation of coefficient was 0.9999 with a y-intercept not significantly di fferent from zero. The inter-day relative standard deviation (RSD) was < 10 % for all three concentrations. The intra-day RSD was 14% for 2 ng mL(-1). This assay was then successfully applied to human serum samples obtained fr om clinical trials after oral administration of salbutamol.