title: Salting-out homogeneous liquid-liquid extraction approach applied in sample pre-processing for the quantitative determination of entecavir in human plasma by LC-MS.
abstract: A convenient, robust, economical and selective sample preparation method for the quantitative determination of entecavir in human plasma by LC-MS was developed and validated. Entecavir and the internal standard of acyclovir were extracted from 500 μL of human plasma by a salting-out homogeneous liquid-liquid extraction approach (SHLLE) with acetonitrile as the organic extractant and magnesium sulfate as the salting-out reagent. They were analyzed on a Hanbon® Lichrospher RP C18 HPLC column (150 mm×2.0 mm; 5 μm) with gradient elution. The mobile phase comprised 0.1% acetic acid-0.2 mmol ammonium acetate in water (mobile phase A) and acetonitrile (mobile phase B). The flow rate is 0.2 mL/min. The analytes were detected by a LC-MS 2010 single quadrupole mass spectrometer instrument equipped with an electrospray ionization interface using selective ion monitoring positive mode. A "post cut" column switch technique was incorporated into the method to remove interferences of earlier and later eluting matrix components than entecavir and internal standard, including salting-out reagent used in sample pre-processing. The method was validated over the concentration range of 0.05-20 ng/mL. The intra-day and inter-day precision of the assay, as measured by the coefficient of variation (%CV), was within 3.59%, and the intra-day assay accuracy was found to be within 4.88%. The average recovery of entecavir was about 50% and the ion suppression was approximately 44% over the standard curve. Comparison of matrix effect between SHLLE and SPE by continuous post column infusion showed that these two methods got similar, slight ion suppression. The SHLLE method has been successfully utilized for the analysis of entecavir in post-dose samples from a clinical study.
authors.affiliation: Center of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University, Nanjing 210009, China.
authors.forename: Feng-Juan
authors.initials: FJ
authors.lastname: Zhao
authors.forename: Hong
authors.initials: H
authors.lastname: Tang
authors.forename: Qing-Hua
authors.initials: QH
authors.lastname: Zhang
authors.forename: Jin
authors.initials: J
authors.lastname: Yang
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Davey
authors.forename: Ji-Ping
authors.initials: JP
authors.lastname: Wang
mesh_terms: D000097:Acetonitriles; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D006147:Guanine / Q000031:analogs & derivatives* / Q000097:blood / Q000302:isolation & purification; D006801:Humans; D016014:Linear Models; D059625:Liquid-Liquid Extraction / Q000379:methods*; D008278:Magnesium Sulfate; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D000097:Acetonitriles; C413685:entecavir; D006147:Guanine; D008278:Magnesium Sulfate; C032159:acetonitrile