Quantifying tetrapeptide SS-20 in rat plasma using hydrophilic interaction liquid chromatography coupled with electrospray ionization tandem mass spectrometry

Quantitative analysis of peptides in biological matrices remains a challenging task. This is due to the low dosage and the complexity of both the matrix and the analytical characteristics of peptides. SS-20 is a tetrapeptide compound developed for the treatment of Parkinson's disease. To investigate the pharmacokinetics of SS-20, a sensitive and rapid liquid chromatography coupled with mass spectrometry method was developed and validated. An aliquot of 50 μL plasma sample was extracted via solid phase extraction. The extracts were separated using a hydrophilic interaction liquid chromatography column, and were then detected with a triple quadrupole mass spectrometer using electrospray ionization in positive-ion mode and selected reaction monitoring. The use of a deuterium-labeled internal standard provided acceptable accuracy, precision, and matrix effect. The lower limit of quantification was 0.30 ng/mL. The linear range of the method was from 0.30 to 1000 ng/mL. The intraday and interday precisions were lower than 10.2% in terms of relative standard deviation, and the accuracy was within ±2.1% in terms of relative error. The validated LC–MS/MS method was successfully applied to a pharmacokinetic study of SS-20 following an intravenous or subcutaneous injection administration of 1.0 mg/kg to Sprague-Dawley rats.