Gas chromatographic–mass spectrometric quantitation of busulfan in human plasma for therapeutic drug monitoring: A new on-line derivatization procedure for the conversion of busulfan to 1,4-diiodobutane

• A simplified GC–MS assay for quantitation of busulfan in plasma was developed.
• A novel on-line derivatization procedure for detection of busulfan is presented.
• Application to case samples demonstrating simplicity, accuracy and selectivity.

A simplified gas chromatographic–mass spectrometric (GC–MS) analytical method, involving a novel derivatization procedure was developed for monitoring busulfan (Bu) plasma concentrations in populations undergoing bone marrow transplantation. Plasma samples (500 μL) containing Bu-d8 as internal standard were extracted with ethyl acetate (2 mL) followed by centrifugation (1800 rpm, 5 min) and evaporation of the organic layer under nitrogen flow (50 °C). The dry residue was reconstituted with 100 μL iodine solution in acetonitrile (0.25%, w/v) and 3 μL were injected into the GC–MS system at 250 °C. Conversion of Bu to 1,4-diiodobutane was accomplished on-line without the need of an extra derivatization step. MS was operated at selected ion monitoring mode at m/z 183 and 191 corresponding to Bu and Bu-d8 derivatives. Total analysis time was 11.5 min. Calibration curves were linear (mean r = 0.9996) over a concentration range of 25–3651 ng/mL using a (1/x)-weighted scheme. Limit of detection and lower limit of quantitation were 10.6 and 25 ng/mL, respectively. Overall accuracy Er (%) was ranging from −5.10% to 10.5%. Within- and between-run RSD (%) were lower 4.51% and 2.15%, respectively. Overall recovery of Bu was equal to 69.3 ± 4.56% (RSD (%)). The present method is sensitive and specific, requiring a simple sample preparation procedure and short analysis time, advantages crucial for therapeutic drug monitoring of Bu in clinical practice and application in pharmacokinetic studies.

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