Quantification of dimethylsulfoxide (DMSO) in equine plasma and urine using HILIC-MS/MS.

This paper describes quantitative methods for the determination of dimethylsulfoxide (DMSO) in equine plasma and urine based on simple precipitation and dilution followed by hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry (HILIC-MS/MS). DMSO is a polar solvent with analgesic and anti-inflammatory properties. Its pharmacological features make it prohibited in horse racing. However, since DMSO is naturally present in the horses' environment, international threshold values have been implemented for plasma and urine (1 and 15 µg/mL, respectively). Previously presented quantitative methods for the determination of DMSO are based on gas chromatography, thus demanding a tedious extraction step to transfer the analyte from the aqueous bodily fluid to an injectable organic solvent. The column used in the presented method was an Acquity BEH HILIC and the mobile phase was a mixture of ammonium acetate buffer and acetonitrile delivered as a gradient. Hexadeuterated DMSO (2 H6 -DMSO) was used as the internal standard. Validation was performed in the range of the international thresholds concerning selectivity, carry-over, linearity, precision, accuracy, stability and inter-individual matrix variation. The results fulfilled the predefined criteria and the methods were considered fit for purpose. Successful applications on real equine doping control samples were carried out with determined DMSO concentrations exceeding the international thresholds. Copyright © 2016 John Wiley & Sons, Ltd.