Analytical methodology for enantiomers of salbutamol in human urine for application in doping control

Liquid chromatographic procedure with fluorimetric detection for chiral separation and quantification of salbutamol enantiomers in urine samples has been developed. The extraction of free salbutamol from urine has been considered using liquid-liquid and solid-phase procedures. The effect of pH, salting-out effect and organic solvent has been studied in liquid-liquid extraction from aqueous and urine samples. For solid-phase extraction, different mechanisms (polar, non-polar, cation-exchange and interactions with a polymeric phase) have been tested and the effect of the urine matrix on the extraction recoveries has been considered. Bond-Elut Certify extraction cartridges provided the best specificity and good recoveries for salbutamol in urine. The sample is acidified, applied to the preconditioned cartridges and, after a washing step, salbutamol enantiomers are eluted with a mixture of chloroform and 2-propanol (80:20, v/v) containing 2% ammonia. Atenolol is used as external standard. Enantioselective separation is accomplished with a Chirex 3022 stationary phase (urea type silica-bonded chiral phase) using a mobile phase containing hexane-dichloromethane-methanol-trifluoroacetic acid (250:218:31:1, v/v) and fluorimetric detection with excitation and emission wavelengths set at 230 and 309 nm, respectively. The method proposed is rapid, selective and sensitive, and seems to be useful to differentiate between an authorized and a prohibited use of the drug in doping control.

Determination of albuterol in plasma after aerosol inhalation by gas chromatography-mass spectrometry with selected-ion monitoring

Albuterol is a beta2-adrenergic agonist commonly used as a bronchodilator for the treatment of patients with asthma. We have developed an assay to determine plasma levels as low as 50 pg/ml of albuterol by gas chromatography-mass spectrometry (GC-MS). This assay utilizes isotopically labeled albuterol ([13C]albuterol) as an internal standard. In this assay albuterol and the internal standard are recovered from 1 ml of plasma using solid-phase extraction. The samples are then derivatized to trimethylsilyl ethers using N,O-bis(trimethylsilyl)trifluoro-acetamide with 1% trimethylchlorosilane. The samples are then analyzed by GC-MS with selected-ion monitoring (SIM) for the ions m/z 369.15 and 370.15. The method has been validated for a concentration range of 50-10000 pg/ml in plasma.

Voltammetric study of salbutamol and application to its determination in a tablet dosage form and dissolution profiles for the dosage form

The oxidative voltammetric behaviour of salbutamol at a glassy carbon electrode surface has been studied using cyclic voltammetry and differential pulse voltammetry. Oxidation of the drug was effected in a single irreversible, adsorption-controlled step in phosphate buffer. The process was found to be dependent on the ionic strength and the pH of the supporting electrolyte. The response was evaluated with respect to accumulation time, scan rate and other variables. Using differential pulse voltammetry following electrochemical pretreatment of the electrode surface, the drug yielded a well-defined voltammetric response in phosphate buffer, pH 5.0, at +0.75 V (vs SCE). This process could be used to determine salbutamol concentrations in the range 8 x 10(-7) M to 8 x 10(-5) M with a detection limit of 2 x 10(-7) M. The method was applied, without any interferences from the excipients, to the determination of the drug in a tablet dosage form and in drug dissolution studies. The absolute recovery for salbutamol was greater than 95% at the concentration levels studied, and reproducible voltammetric signals were obtained with a relative standard deviation of 2.4% for n = 7 at a concentration level of 8 x 10(-5) M.

Simultaneous determination of salbutamol and terbutaline at overdose levels in human plasma by high performance liquid chromatography with electrochemical detection

A multidimensional column chromatographic method involving electrochemical detection using a carbon fibre microelectrode flow cell was optimized and successfully applied to the simultaneous determination of salbutamol and terbutaline in plasma at overdose levels. This method performs, in a single step, an efficient extraction and clean-up of salbutamol and terbutaline from human plasma. The calibration graphs over three days were linear over the calibration range 20-100 ng/mL plasma with a limit of detection of 1 ng and 0.8 ng/mL plasma for salbutamol and terbutaline, respectively. The intra- and inter-assay coefficients of variation were less than 8% and the recoveries ranged from 94 to 96%. The accuracy of the assay, which was defined as the percentage difference between the mean concentration found and the theoretical concentration, was 7% or better. The proposed method combines the advantages of being simple, reproducible and selective in the presence of other sympathomimetic and commonly ingested drugs and is suitable for routine analyses to obtain valuable information about the clinical effects and treatment of overdose with these drugs. The whole procedure takes ca. 10 min and compares favourably with detection at a conventional glassy carbon electrode.