Stable isotope labeling derivatization coupled with magnetic dispersive solid phase extraction for the determination of hydroxyl-containing cholesterol and metabolites by in vivo microdialysis and ultra-high performance liquid chromatography tandem mass spectrometry.

Hydroxyl-containing cholesterol and metabolites (HCMs) are potential biomarkers for Alzheimer's disease. Therefore, quantitative analysis of HCMs can serve as an indicator of clinical diagnosis and drug treatment. In this work, we developed an accurate, sensitive and rapid method for the determination of HCMs in rat blood microdialysates by microwave-assisted stable isotope labeling derivatization (MA-SILD) magnetic dispersive solid phase extraction (MDSPE) coupled with ultra-high performance liquid chromatography electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS) in the multiple reaction monitoring mode (MRM). In this respect, a pair of new SILD reagents, d-/d-3-N-methyl-2'-carboxyl Rhodamine 6G (d-/d-MCR6G), were designed, synthesized and used to label HCMs. Rhodamine 6G with permanently positive charge was introduced into HCMs, improving ionization efficiency and enhancing detection sensitivity. In addition, the d-MCR6G labeled standards were served as internal standards, reducing the matrix effect and guaranteeing accurate quantification. Various factors affecting MA-SILD and MDSPE were optimized. Furthermore, good linearity was obtained with R > 0.994 over the concentration range of 2-3000 pg/mL. The limits of detection (LODs) and quantitation (LOQs) were in the range of 0.24-0.31 and 1.5-1.8 pg/mL, respectively. Acceptable precision (1.6-12.6%), accuracy (87.9-105.2%), matrix effect (85.4-111.2%) and derivatization efficiency (>98%) were achieved. On the whole, this method was validated and applied to accurate, sensitive and simple quantitation of HCMs in rat blood microdialysates. This work would provide some technical support in the diagnosis and treatment of AD or other neurological diseases.