title: Identification and elimination of ion suppression in the quantitative analysis of sirolimus in human blood by LC/ESI-MS/MS.
abstract: Ion suppression can negatively affect the performance characteristics of LC/ESI-MS/MS based methods, and we wished to identify sources of ion suppression in an assay for quantitating sirolimus in human whole blood. We first compared the peak areas of sirolimus and ascomycin added to human blood samples treated with and without extraction using octadecyl silyl (ODS)-silica gel after protein precipitation, and we found that water-soluble compounds cause the ion suppression for both drugs. Post-column infusion studies indicated that compounds retained in the sample after ODS extraction and protein precipitation caused ion suppression. MS analysis of these compounds suggested they were hydroxyl group-possessing phosphocholines, and this was confirmed using purified lysophosphatidylcholine variants. Therefore, we included a HybridSPE treatment step after the ODS extraction into the preanalytical workflow to remove phosphocholines, and this successfully eliminated the observed ion suppression for determining sirolimus concentration in human whole blood by LC/ESI-MS/MS. Sirolimus is a highly lipophilic molecule, and this study demonstrates the impact that preanalytical extraction and purification steps can have on a laboratory's ability to accurately detect and quantitate this and other lipophilic drugs.
authors: Department of Pharmaceutical Sciences, Tohoku University Hospital, Aoba-ku, Sendai, Japan. mano@hosp.tohoku.ac.jp
authors: Nariyasu
authors: N
authors: Mano
authors: Marina
authors: M
authors: Nozawa
authors: Mayumi
authors: M
authors: Sato
authors: Masaru
authors: M
authors: Mori
authors: Hiroaki
authors: H
authors: Yamaguchi
authors: Katsuhiro
authors: K
authors: Kanda
authors: Makoto
authors: M
authors: Nogami
authors: Junichi
authors: J
authors: Goto
authors: Miki
authors: M
authors: Shimada
mesh_terms: D001798:Blood Proteins / Q000302:isolation & purification; D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D010743:Phospholipids / Q000302:isolation & purification; D020123:Sirolimus / Q000097:blood* / Q000737:chemistry; D052616:Solid Phase Extraction; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D016559:Tacrolimus / Q000031:analogs & derivatives / Q000097:blood; D053719:Tandem Mass Spectrometry / Q000379:methods
chemical_list: D001798:Blood Proteins; D010743:Phospholipids; C058028:immunomycin; D020123:Sirolimus; D016559:Tacrolimus