Development of solid phase extraction strategies to minimize the effect of human urine matrix effect on the response of carnitine by UPLC–MS/MS

Abstract

A rapid, selective and sensitive ultra-high performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method was developed to determine carnitine in human urine. Solid phase extraction approaches based on the use of polymeric and weak cationic exchange cartridges were evaluated and applied to the treatment of urine samples. After optimizing the various stages of SPE, a satisfactory set up for retaining substances interfering on carnitine's response was achieved for both types of cartridges. The UPLC separation was carried out on a reversed phase column. The detection was performed on a triple quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) mode via electrospray ionization (ESI) source. Residual matrix components were specific to urine samples and interfered on the carnitine signal (a response suppression of 50% was observed). It was then demonstrated that sample treatment by SPE could reduce the effect of the above mentioned interferents, without needing a preliminary derivatization step. The recovery percentage of carnitine obtained after the application of SPE was of approximately 83 ± 7% and, consequently, the matrix effect was minimized. Thus, a sensitive, precise and reliable methodology was developed to determine traces of carnitine in biological fluids.