Gas chromatographic–mass spectrometry method for the detection of busulphan and its metabolites in plasma and urine

Busulphan is an alkylating agent used as conditioning regimen prior to stem cell transplantation. Busulphan is metabolized in the liver and four major metabolites have been identified. The first metabolite is tetrahydrothiophene which is oxidized to tetrahydrothiophene 1-oxide, then sulfolane and finally 3-hydroxy sulfolane. Despite the low molecular weight and wide polarity range of busulphan and its four metabolites, the use of a fused silica non-polar column significantly enhanced the automated gas chromatography–mass spectrometry of their detection in one simple method. The limit of quantification was 0.5 μM for busulphan and all its metabolites except 3-OH sulfolane, which was 1.25 μM. This method was validated for all the compounds in both human plasma and urine. Lower limits of quantifications (LLOQs) were run in pentaplicate per compound and all results were within 20% of the nominal values. The recovery was determined by comparing the peak area of two quality control (QC) samples, before and after extraction in plasma and urine, in triplicate. Acceptable precision and accuracy have been obtained; at least 3 standard curves have been run for each compound using three different QCs covering the calibration curve in triplicate. The QC values were within 15% (SD) of the nominal values. Selectivity and sensitivity of all compounds have been measured. Compounds were stable up to 50 days after extraction in −20 °C and 48 h at RT. Moreover, the compounds were stable for three cycles of freezing and thawing. The method was applied in a clinical case where the patient received high dose busulphan; all the compounds have been detected, identified and quantified both in plasma and urine.