Overcoming interference with the detection of a stable isotopically labeled microtracer in the evaluation of beclabuvir absolute bioavailability using a concomitant microtracer approach.

The oral absolute bioavailability of beclabuvir in healthy subjects was determined using a microdose (100μg) of the stable isotopically labeled tracer via intravenous (IV) infusion started after oral dosing of beclabuvir (150mg). To simultaneously analyze the concentrations of the IV microtracer ([C]beclabuvir) and beclabuvir in plasma samples, a liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS) method was initially developed. Surprisingly beclabuvir significantly interfered with the IV microtracer detection when using the selected reaction monitoring (SRM) in the assay.

Improved ruggedness of an ion-pairing liquid chromatography/tandem mass spectrometry assay for the quantitative analysis of the triphosphate metabolite of a nucleoside reverse transcriptase inhibitor in peripheral blood mononuclear cells.

Rationale: Nucleotide analogs are highly polar and ionic, which impose great challenges on bioanalysis. Ion-pairing liquid chromatography/tandem mass spectrometry (LC/MS/MS) is the predominant reported approach for such compounds. Assay ruggedness of ion-pairing LC/MS/MS methods was often a challenge due to the potential contamination of the ion source of the mass spectrometer and LC column performance deterioration caused by ion-pairing reagents.

Theory-guided efficient strategy to maximize speed and resolution in rapid gradient LC-MS/MS bioanalysis.

Reversed-phase gradient LC-MS/MS bioanalytical methods of 5-100% organic solvent in a 1-3 min gradient time are common in today's bioanalytical laboratory. The goal of this work was to develop a theory-guided systematic strategy for maximizing resolution and speed in rapid gradient LC-MS/MS bioanalysis. We studied the effect of gradient time (t(G)), initial and final eluent strength (% B=% organic), and flow rate (F) on the separation of multiple critical pairs (R(s)) and peak capacity (n(c)) in a gradient elution of a mixture of five structurally related compounds.

Effect of mobile phase pH, aqueous-organic ratio, and buffer concentration on electrospray ionization tandem mass spectrometric fragmentation patterns: implications in liquid chromatography/tandem mass spectrometric bioanalysis.

Liquid chromatography/tandem mass spectrometry (LC/MS/MS) based on selected reaction monitoring (SRM) is the standard methodology in quantitative analysis of administered xenobiotics in biological samples. Utilizing two SRM channels during positive electrospray ionization (ESI) LC/MS/MS method development for a drug compound containing two basic functional groups, we found that the response ratio (SRM1/SRM2) obtained using an acidic mobile phase was dramatically different from that obtained using a basic mobile phase. This observation is different from the well-established phenomenon of mobile phase affecting the [M+H](+) response, which is directly related to the amount of the [M+H](+) ions produced during the ionization.

A sensitive method for the determination of entecavir at picogram per milliliter level in human plasma by solid phase extraction and high-pH LC-MS/MS.

Entecavir is a guanine nucleoside analogue used in the treatment of hepatitis B virus (HBV) infection. In this paper, we describe an LC-MS/MS method that was developed and validated for the quantitation of entecavir in human EDTA plasma with both high sensitivity (lower limit of quantitation (LLOQ) of 5 pg/mL) and a wide concentration range (5000-fold) intended for low dose ascending clinical studies. High enrichment was achieved by taking advantage of the excellent loading capacity and reproducibility of Oasis HLB 96-well solid phase extraction plate, which allowed 1 mL of plasma samples to be processed in two equal sequential loading steps.