title: Ultrafast selective quantification of methotrexate in human plasma by high-throughput MALDI-isotope dilution mass spectrometry.
abstract: BACKGROUND
  A new analytical MS method using isotope dilution combined with MALDI-triple quadrupole MS/MS has been developed and validated for the determination of methotrexate and 7-hydroxymethotrexate in plasma. Methotrexate, methotrexate-d3, 7-hydroxymethotrexate and 7-hydroxymethotrexate-d3 were monitored by selected reaction monitoring using the transitions m/z 455.2→308.2, 458.2→311.2, 471.2→324.2 and 474.2→327.2 for methotrexate, methotrexate-d3, 7-hydroxymethotrexate and 7-hydroxymethotrexate-d3, respectively.
  
  
  RESULTS
  The LLOQ was 1 nmol/l for methotrexate and 7-hydroxymethotrexate while the limit of detection was 0.3 nmol/l for both analytes. The new developed method was cross-validated by a fluorescence polarization immunoassay and tested for its clinical feasibility by measuring plasma samples from patients suffering from acute lymphoblastic leukemia. Plasma methotrexate concentrations ranged between 66.0 and 954 nmol/l and observed 7-hydroxymethotrexate/methotrexate ratios ranged between 0.1 and 32.4, respectively.
  
  
  CONCLUSIONS
  The new method showed comparable analytical performances as the fluorescence polarization immunoassay, but analyte specificity and sensitivity of the newly developed method were significantly better.
authors.affiliation: Laboratories of Neuro-Oncology & Clinical & Cancer Proteomics, Department of Neurology, University Medical Center Rotterdam (ErasmusMC), Dr. Molewaterplein 50, Room Ee-1981, 3015 GE Rotterdam, The Netherlands. r.meesters@erasmusmc.nl
authors.forename: Roland J W
authors.initials: RJ
authors.lastname: Meesters
authors.forename: Ethan
authors.initials: E
authors.lastname: den Boer
authors.forename: Ron A A
authors.initials: RA
authors.lastname: Mathot
authors.forename: Robert
authors.initials: R
authors.lastname: de Jonge
authors.forename: Rob J
authors.initials: RJ
authors.lastname: van Klaveren
authors.forename: Jan
authors.initials: J
authors.lastname: Lindemans
authors.forename: Theo M
authors.initials: TM
authors.lastname: Luider
mesh_terms: D003903:Deuterium; D004355:Drug Stability; D016231:Fluorescence Polarization Immunoassay; D006801:Humans; D008727:Methotrexate / Q000031:analogs & derivatives / Q000097:blood* / Q000633:toxicity; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000097:blood; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods
chemical_list: D003903:Deuterium; C011864:7-hydroxymethotrexate; D008727:Methotrexate