title: Liquid chromatography-mass spectrometry with on-line solid-phase extraction by a restricted-access C18 precolumn for direct plasma and urine injection.
abstract: In this paper, the on-line coupling of solid-phase extraction, based on a restricted-access support with liquid chromatography-mass spectrometry (LC-MS), for the analysis of biological samples is described. The system was tested with cortisol and prednisolone for plasma analysis and arachidonic acid for urine analysis. A precolumn packed with a 25-micron C18 alkyl-diol support is used for direct plasma or urine injection. Using column-switching techniques, the analytes enriched on the precolumn are eluted to the analytical column without transfer loss. An on-line heart-cut technique was employed and only the analyte-containing fraction eluting from the LC column is directed to the MS to protect the LC-MS interface and ion-source from contamination. The whole system is operated in a parallel mode, that is, sample pre-treatment and LC-MS analysis are performed simultaneously to provide the shortest possible analysis time. The only off-line sample pre-treatment step required was centrifugation to remove particulate matter. With the fully automated system, total analysis times of 5 and 9.5 min were achieved for cortisol in serum and arachidonic acid in urine, respectively. Cortisol and related compounds were quantitatively recovered from plasma with a detection limit for prednisolone (direct injection of 100 microliters on restricted-access precolumn) of 2 ng/ml.
authors.affiliation: Division of Analytical Chemistry, Leiden/Amsterdam Centre for Drug Research, Leiden University, Netherlands.
authors.forename: R A
authors.initials: RA
authors.lastname: van der Hoeven
authors.forename: A J
authors.initials: AJ
authors.lastname: Hofte
authors.forename: M
authors.initials: M
authors.lastname: Frenay
authors.forename: H
authors.initials: H
authors.lastname: Irth
authors.forename: U R
authors.initials: UR
authors.lastname: Tjaden
authors.forename: J
authors.initials: J
authors.lastname: van der Greef
authors.forename: A
authors.initials: A
authors.lastname: Rudolphi
authors.forename: K S
authors.initials: KS
authors.lastname: Boos
authors.forename: G
authors.initials: G
authors.lastname: Marko Varga
authors.forename: L E
authors.initials: LE
authors.lastname: Edholm
mesh_terms: D016718:Arachidonic Acid / Q000652:urine; D001774:Blood Chemical Analysis / Q000379:methods*; D002853:Chromatography, Liquid / Q000379:methods*; D005438:Fludrocortisone / Q000097:blood; D006854:Hydrocortisone / Q000097:blood; D013058:Mass Spectrometry / Q000379:methods*; D009862:Online Systems; D011239:Prednisolone / Q000097:blood; D016482:Urinalysis / Q000379:methods*
chemical_list: D016718:Arachidonic Acid; D011239:Prednisolone; D005438:Fludrocortisone; D006854:Hydrocortisone