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

This research paper presents a new method for precisely measuring the amount of dimethylsulfoxide (DMSO), a substance prohibited in horse racing, in horses’ plasma and urine. The proposed method is easier and more efficient in comparison to previous methods.

Understanding Dimethylsulfoxide (DMSO)

• Dimethylsulfoxide (DMSO) is a polar solvent known for its analgesic and anti-inflammatory properties.
• In the context of horse racing, it is a prohibited substance due to its potential to unfairly affect the performance of a horse.
• However, as it is naturally present in the environment of horses, international threshold values have been set for its levels in plasma and urine – 1 and 15 µg/mL respectively.

Previous DMSO Quantification Methods

• The quantification of DMSO was traditionally carried out using gas chromatography.
• This method involved a complex extraction step whereby the DMSO had to be transferred from the aqueous bodily fluid to an injectable organic solvent.

New Quantification Method

• The researchers presented a new method using hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry (HILIC-MS/MS).
• This method simplifies the process by directly precipitating and diluting the sample before analysis.
• In this protocol, an Acquity BEH HILIC column was used, and the mobile phase was a mixture of ammonium acetate buffer and acetonitrile.
• A substance known as hexadeuterated DMSO (H-DMSO) was used as the internal standard against which the quantity of DMSO could be measured.

Validation and Application

• The new method was validated with respect to several factors such as selectivity, carry-over, linearity, precision, accuracy, stability, and inter-individual matrix variation.
• The results were found to meet the predefined criteria, indicating the new method to be effective.
• The method was successfully applied on real equine doping control samples, where the DMSO concentrations recorded exceeded the international thresholds.