Simultaneous analysis of tiaramide metabolites in horse urine and plasma by solid-phase extraction and reversed-phase ion-pair liquid chromatography.

The research article presents a simple yet effective method for analyzing metabolites of a drug called tiaramide (TRA) in horse urine and plasma. It details the sample preparation, extraction, reagents used, and their recoverability.

Sample Preparation and Extraction

• The scientists describe the sample preparation method using a Bond-Elut PH cartridge. The cartridge is a bond chemical that aids in the extraction and clean-up process for the plasma and urine samples.
• The extraction method involves a stepwise elution process using ice-cold, 30% aqueous methanol, followed by additional methanol. ‘Elution’ in this case means the act of extracting one material from another by washing with a solvent.
• The method is deemed effective as it allows good recoveries, extracting more than 80% of the metabolites, and has high reproducibility, meaning the method can be repeated with the same results.

Metabolite Analysis

• The extracted metabolites are then analyzed by high-performance liquid chromatography, a laboratory method for the separation, identification, and quantification of each component in a mixture.
• The tool uses an octadecyl-type column filled with polymer-based packing material. A solvent system containing a phosphate buffer, acetonitrile, tetrahydrofuran, and a quaternary ammonium salt is used for the process. The quaternary ammonium salt acts as an ion-pairing reagent and aids in the separation of the metabolites.
• The low detection limit of the method—all metabolites can be traced within a range of 20-80 ng/ml—proves its efficiency.

Metabolite Identification

• The major metabolites of TRA found in equine urine and plasma are N-acetic acid (TRAA) and an N-oxide. The N-oxide of TRAA is also detected as a metabolite in the urine.
• A dealkylation product, potential evidence of the metabolic process, is found as a minor metabolite. Dealkylation refers to the process of removing an alkyl group—essentially a piece of a molecule—thus, the metabolite found in the urine reflects this change.
• The unchanged TRA is found only at low concentrations in the urine, indicating the metabolization of the drug by the horse’s body.
• The researchers also report finding several minor metabolites in the urine. These metabolites could be resultant from either TRA or TRAA or both, providing additional insight into the metabolic process.