Validation of a liquid chromatography-tandem mass spectrometry method for simultaneous quantification of N,N-dimethylacetamide and N-monomethylacetamide in paediatric plasma.

N,N-dimethylacetamide is an excipient used in intravenous busulfan formulations, administered prior to haematopoietic stem cell transplantation. This study aimed to develop and validate a liquid chromatography-tandem mass spectrometry method for simultaneous quantification of N,N-dimethylacetamide and its metabolite N-monomethylacetamide in paediatric plasma for patients receiving busulfan. A 4 μL aliquot of patient plasma was extracted using 196 μL 50% methanol solution and quantified against calibrators prepared in the extraction solvent given negligible matrix effects across three concentrations. 9 [H 2 ]-N,N-dimethylacetamide was used as an internal standard. Separation of N,N-dimethylacetamide and N-monomethylacetamide was achieved using a Kinetex® EVO C18 stationary phase (100mm × 2.1mm × 2.6μm) running an isocratic mobile phase of 30% methanol containing 0.1% formic acid at a flow of 0.2 mL/min over 3.0 minutes and an injection volume of 1 μL. N,N-dimethylacetamide and N-monomethylacetamide were linear up to 1200 μg/L and 200 μg/L (lower limit of quantification 1 μg/L for both analytes), respectively. Calibrator accuracy and precision were within ± 10% of the test parameters across four concentration levels. Analytes were stable over 14 days at three different storage conditions. This method was successfully applied to measure N,N-dimethylacetamide and N-monomethylacetamide concentrations in 77 paediatric patients, totalling 1,265 plasma samples. This article is protected by copyright. All rights reserved.