Combining restricted access material (RAM) and turbulent flow for the rapid on-line extraction of the cyclooxygenase-2 inhibitor rofecoxib in plasma samples

Restricted-access media supports for direct high-throughput analysis of biological fluid samples: review of recent applications

This review presents an update on the use of restricted-access materials (RAMs) for direct injection of biological samples. The fundamental improvements in the preparation of tailored RAMs and the diversity of applications with these phases are presented. Insights into diminishing the matrix effect by the use of RAM supports in methods by LC–MS and into the low number of methods for enantiomeric separations by direct injections of biological samples are addressed. The diversity of systems that incorporate RAMs for selective sample clean-up or fractionation in proteome and peptidome analysis is also covered.

Development of a quantitative LC–MS/MS analytical method coupled with turbulent flow chromatography for digoxin for the in vitro P-gp inhibition assay

Caco-2 cells, the human colon carcinoma cells, are typically used for screening compounds for their permeability characteristics and P-glycoprotein (P-gp) interaction potential during discovery and development. The P-gp inhibition of test compounds is assessed by performing bi-directional permeability studies with digoxin, a well established P-gp substrate probe. Studies performed with digoxin alone as well as digoxin in presence of test compounds as putative inhibitors constitute the P-gp inhibition assay used to assess the potential liability of discovery compounds. Radiolabeled (3)H-digoxin is commonly used in such studies followed by liquid scintillation counting. This manuscript describes the development of a sensitive, accurate, and reproducible LC-MS/MS method for analysis of digoxin and its internal standard digitoxin using an on-line extraction turbulent flow chromatography coupled to tandem mass spectrometric detection that is amendable to high throughput with use of 96-well plates. The standard curve for digoxin was linear between 10 nM and 5000 nM with regression coefficient (R(2)) of 0.99. The applicability and reliability of the analysis method was evaluated by successful demonstration of efflux ratio (permeability B to A over permeability A to B) greater than 10 for digoxin in Caco-2 cells. Additional evaluations were performed on 13 marketed compounds by conducting inhibition studies in Caco-2 cells using classical P-gp inhibitors (ketoconazole, cyclosporin, verapamil, quinidine, saquinavir etc.) and comparing the results to historical data with (3)H-digoxin studies. Similarly, P-gp inhibition studies with LC-MS/MS analytical method for digoxin were also performed for 21 additional test compounds classified as negative, moderate, and potent P-gp inhibitors spanning multiple chemo types and results compared with the historical P-gp inhibition data from the (3)H-digoxin studies. A very good correlation coefficient (R(2)) of 0.89 between the results from the two analytical methods affords an attractive LC-MS/MS analytical option for labs that need to conduct the P-gp inhibition assay without using radiolabeled compounds.

Recent advances in high-throughput quantitative bioanalysis by LC–MS/MS

Liquid chromatography linked to tandem mass spectrometry (LC-MS/MS) has played an important role in pharmacokinetics and metabolism studies at various drug development stages since its introduction to the pharmaceutical industry. This article reviews the most recent advances in sample preparation, separation, and the mass spectrometric aspects of high-throughput quantitative bioanalysis of drug and metabolites in biological matrices. Newly introduced techniques such as ultra-performance liquid chromatography with small particles (sub-2 microm) and monolithic chromatography offer improvements in speed, resolution and sensitivity compared to conventional chromatographic techniques. Hydrophilic interaction chromatography (HILIC) on silica columns with low aqueous/high organic mobile phase is emerging as a valuable supplement to the reversed-phase LC-MS/MS. Sample preparation formatted to 96-well plates has allowed for semi-automation of off-line sample preparation techniques, significantly impacting throughput. On-line solid-phase extraction (SPE) utilizing column-switching techniques is rapidly gaining acceptance in bioanalytical applications to reduce both time and labor required to produce bioanalytical results. Extraction sorbents for on-line SPE extend to an array of media including large particles for turbulent flow chromatography, restricted access materials (RAM), monolithic materials, and disposable cartridges utilizing traditional packings such as those used in Spark Holland systems. In the end, this paper also discusses recent studies of matrix effect in LC-MS/MS analysis and how to reduce/eliminate matrix effect in method development and validation.

Automated liquid chromatography–tandem mass spectrometry method for the analysis of firocoxib in urine and plasma from horse and dog

A rugged, sensitive and efficient liquid chromatography-tandem mass spectrometry method was developed and validated for the quantitative analysis of firocoxib in urine from 5 to 3000 ng/mL and in plasma from 1 to 3000 ng/mL. The method requires 200 microL of either plasma or urine and includes sample preparation in 96-well solid phase extraction (SPE) plates using a BIOMEK 2000 Laboratory Automated Workstation. Chromatographic separation of firocoxib from matrix interferences was achieved using isocratic reversed phase chromatography on a PHENOMENEX LUNA Phenyl-Hexyl column. The mobile phase was 45% acetonitrile and 55% of a 2 mM ammonium formate buffer. The method was accurate (88-107%) and precise (CV<12.2%) within and between sets. Extraction efficiencies (recovery)>93% were achieved and ionization efficiencies (due to matrix effects) were >72%. Extensive stability and ruggedness testing was also performed; therefore, the method can be used for pharmacokinetic studies as well as drug monitoring and screening. The data presented here is the first LC-MS/MS method for the quantitation of firocoxib in plasma (LLOQ of 1 ng/mL), a 25-fold improvement in sensitivity over the HPLC-UV method and the first quantitative method for firocoxib in urine (LLOQ of 5 ng/mL). Additionally the sample preparation process has been automated to improve efficiency.

Recent developments in extraction procedures relevant to analytical toxicology

Sample preparation is an important step in the development of an analytical method but is often regarded as time-consuming, laborious work. Optimum sample preparation leads to enhanced selectivity and sensitivity, however, and reduces amounts of interfering matrix compounds, resulting in less signal suppression or enhancement. Recent developments in extraction techniques that could be of interest in clinical and forensic toxicology, for example liquid-liquid, solid-phase, and headspace extraction, are summarized in this review. The advantages and disadvantages of several extraction techniques are discussed, to enable the reader to choose an appropriate method of extraction for his or her application. Attention is paid to current trends in analytical toxicology, for example miniaturization, high throughput, and automation.

Transition from creeping via viscous-inertial to turbulent flow in fixed beds

This review is concerned with the analysis of flow regimes in porous media, in particular, in fixed beds of spherical particles used as reactors in engineering applications, or as separation units in liquid chromatography. A transition from creeping via viscous-inertial to turbulent flow is discussed based on macro-scale transport behaviour with respect to the pressure drop-flow rate dependence, in particular, the deviation from Darcy's law, as well as direct microscopic data which reflect concomitant changes in the pore-level hydrodynamics. In contrast to the flow behaviour in straight pipes, the transition from laminar to turbulent flow in fixed particulate beds is not sharp, but proceeds gradually through a viscous-inertial flow regime. The onset of this steady, nonlinear regime and increasing role of inertial forces is macroscopically manifested in the failure of Darcy's law to describe flow through fixed beds at higher Reynolds numbers. While the physical reasons for this failure still are not completely understood, it is not caused by turbulence which occurs at Reynolds numbers about two orders of magnitude above those for which a deviation from Darcy's law is observed. Microscopic analysis shows that this steady, nonlinear flow regime is characterized by the development of an inertial core in the pore-level profile, i.e., at increasing Reynolds number velocity profiles in individual pores become flatter towards the center of the pores, while the velocity gradient increases close to the solid-liquid interface. Further, regions with local backflow and stationary eddies are demonstrated for the laminar flow regime in fixed beds. The onset of local fluctuations (end of laminar regime) is observed at superficial Reynolds numbers on the order of 100. Complementary analysis of hydrodynamic dispersion suggests that this unsteady flow accelerates lateral equilibration between different velocities in fixed beds which, in turn, reduces spreading in the longitudial (macroscopic flow) direction.