On-line derivatization utilizing solid-phase microextraction (SPME) for determination of busulphan in plasma using gas chromatography-mass spectrometry (GC-MS)

Busulphan (Bu) is an alkylating agent used in preparative regimen before stem cell transplantation (SCT). Bu has a narrow therapeutic window, and underdosing or overdosing may have a fatal outcome for the patient. Therapeutic drug monitoring (TDM) combined with dose adjustment is currently used to optimize and individualize therapy with Bu. However, this approach is limited to centers with laboratory facilities. An automated and easy method for measurement of Bu plasma concentrations may facilitate TDM for Bu and thus improve the clinical outcome. A solid-phase microextraction (SPME) on line with gas chromatography (GC) and mass-spectrometric detection to quantify Bu in human plasma samples was developed using in-vial derivatization. Bu was mixed with reagent in a 2-mL vial and shaken for 15 minutes at 80degreesC; subsequently, the SPME fiber was immersed into the vial for 15 minutes. The fiber was washed in water for 10 seconds before injection. Several parameters influencing the extraction and recovery were studied, such as absorption and desorption times, the effects of the temperature on the reaction, and the shaking time on the derivatization yield. Carbowax-divinylbenzene, polyacrylate, and polydimethylsiloxane fibers were tested. The carbowax-divinylbenzene fiber resulted in the highest recovery in plasma samples. The validation of the method showed a high chromatographic selectivity and a good sensitivity (LOQ = 20 ng/mL). Coefficient of variation for SPME was less than 15%. The results showed good correlation between Bu concentrations and response within the range of 40 to 2500 ng/mL (R-2 = 0.999). The accuracy ranged from 94% to 106%. This is well in line with the international criteria for validation. The present method was applied to patient plasma. The obtained results were comparable with the results obtained from GC with electron capture detection. The authors conclude that this method has shortened the analysis time considerably and is fully automated, which benefits TDM of Bit in SCT patients.