Using total error concept for the validation of a liquid chromatography–tandem mass spectrometry method for the determination of budesonide epimers in human plasma

A robust, sensitive and selective method to quantify budesonide epimers in human plasma using solid-phase extraction and liquid chromatography–tandem mass spectrometry (LC–MS/MS) was developed and fully validated. The drug was first isolated from the biological matrix by automated solid-phase extraction (SPE) on disposable extraction cartridges (C-2). The methanolic eluate was then collected and evaporated to dryness. The residue was dissolved in mobile phase and an aliquot was injected onto a Phenomenex Luna octadecylsilica (C-18) column (50 mm × 4.6 mm i.d., 3 μm). The mobile phase is composed of water containing 10 mM ammonium acetate adjusted to pH 3.2 with glacial acetic acid and acetonitrile (65:35, v/v). The flow-rate was 1.00 ml/min. Hydrocortisone acetate was used as internal standard (IS). Detection of the analytes was achieved using negative atmospheric pressure chemical ionization (APCI) tandem mass spectrometry in selected reaction monitoring (SRM) mode. The MS/MS ion transitions monitored were m/z 489.3 → 357.3 and 463.3 → 403.2 for budesonide epimers and hydrocortisone, respectively. The method was validated using SFSTP (2003) proposal based on total measurement error and accuracy profiles as a decision tool. The most appropriate regression model for the response function as well as the limit of quantitation was first selected during the prevalidation step. These latter criteria were then assessed during the formal validation step. The limit of quantitation (LOQ) was around 50 pg/ml for budesonide epimers. The method was validated with respect to stability, recovery, linearity, precision, trueness and accuracy. Risk and uncertainty were also evaluated. The validated method was finally applied successfully to investigate the plasma concentration of budesonide epimers in a pharmacokinetic study.