Stable isotopic internal standard correction for quantitative analysis of hydroxyeicosatetraenoic acids (HETEs) in serum by on-line SPE–LC–MS/MS in selected reaction monitoring mode

The influence of the inclusion of a stable isotopic labeled internal standard (SIL-IS) on the quantitative analysis of hydroxyeicosatetranoic acids (HETEs) in human serum is evaluated in this research. A solid-phase extraction–liquid chromatography–tandem mass spectrometry (SPE–LC–MS/MS) platform, one of the preferred approaches for targeted analysis of biofluids through the selected reaction monitoring (SRM) operational mode, was used to determine HETEs. These compounds were chosen as targeted metabolites because of their involvement in cardiovascular disease, cancer and osteoporosis. 15HETE-d8 was chosen as internal standard to evaluate matrix effects. Thus, the physico-chemical properties of the SIL-IS were the basis to evaluate the analytical features of the method for each metabolite through four calibration models. Two of the models were built with standard solutions at different concentration levels, but one of the calibration sets was spiked with an internal standard (IS). The other two models were built with the serum pool from osteoporotic patients, which was spiked at different concentrations with the target analytes. In this case, one of the serum calibration sets was also spiked with the IS. The study shows that the IS allowed noticeable correction of matrix effects for some HETE isomers at certain concentration levels, while accuracy was decreased at low concentration (15 ng/mL) of them. Therefore, characterization of the method has been properly completed at different concentration levels.