Automatic solid-phase extraction and high-performance liquid chromatographic determination of quinidine in plasma

Quantification of sifuvirtide in monkey plasma by an on-line solid-phase extraction procedure combined with liquid chromatography/electrospray ionization tandem mass spectrometry

A simple, automated and rapid method has been developed for the determination of a novel antiviral peptide sifuvirtide in monkey plasma. Raw plasma samples were directly loaded onto an on-line solid-phase extraction (SPE) column, which removes the time-consuming and laborious sample pretreatment. Following a timed valve-switching event, the analyte was eluted on-line to a reversed-phase high-performance liquid chromatography (RP-HPLC) column and subsequently introduced into a linear ion trap mass spectrometer, LTQ-MS, via an electrospray ionization (ESI) interface. The multiply charged peptides were specified and quantitatively analyzed using selective reaction monitoring (SRM). A highly pure four iodine-sifuvirtide was synthesized using an optimized iodogen method and proved to be a suitable internal standard (IS). A single analysis run takes about 18 min. Validation of the method demonstrated that the linear calibration curves covered the range of 4.88-5000 ng/mL, and the correlation coefficients were above 0.9923. The limit of detection (LOD) with the signal-to-noise (S/N) ratio higher than 12 was calculated as 1.22 ng/mL. The intra- and inter-batch precisions were less than 12.7% and 9.1%, and the mean accuracy ranged from -5.2% to 3.6%, respectively. Any carry-over effect from the system was negligible. In a pharmacokinetic (PK) study of sifuvirtide after a single intravenous or subcutaneous dose in monkeys, the on-line SPE-LC/MS/MS system was successfully utilized to determine hundreds of samples with only one extraction column, which indicated the feasibility and the reliability of this method for application in preclinical and clinical PK studies of peptide drugs.

High-throughput selected reaction monitoring liquid chromatography-mass spectrometry determination of methylphenidate and its major metabolite, ritalinic acid, in rat plasma employing monolithic columns

This work presents a high-throughput selected reaction monitoring (SRM) LC-MS method for the determination of methylphenidate (MPH), a central nervous stimulant, and its de-esterified metabolite, ritalinic acid (RA) in rat plasma samples. A separation of these two compounds was achieved in 15 s by employing a 3.5-ml/min flow-rate, a porous monolithic column and a TurboIonSpray source compatible with relatively high flow-rates. In addition, a relatively fast autosampler and a new data acquisition system resulted in a time lag of less than 17 s between consecutive injections. Overall, 768 protein-precipitated rat plasma samples (eight 96-well plates) containing both MPH and RA were analyzed within 3 h and 45 min. The partial method validation described in this report included an assessment of linearity, intra and inter-assay precision and accuracy, and method robustness. Deuterated internal standards for the target compounds, d(3)-MPH and d(5)-RA, were employed. The calibration curves ranged from 0.1 to 50 ng/ml for MPH and from 0.5 to 50 ng/ml for RA. The limit of quantification (LOQ) for MPH and RA was 0.1 and 0.5 ng/ml, respectively. For both analytes, the intra- and inter-assay precision (relative standard deviation, % C.V.) and accuracy (relative error) did not exceed 15% for the quality control samples (QCs) QC1, QC2 or QC3 (0.3, 1.5 and 40 ng/ml for MPH and 0.15, 15 and 40 ng/ml for RA) for either analyte and did not exceed 20% at the lower limit of quantitation (LOQ) level. No carry-over from the autosampler was detected. The retention times remained constant throughout the experiment. Baseline resolution of MPH and RA was consistently observed throughout the plates analyzed. The described method demonstrates the feasibility for employing monolithic HPLC columns to effect rapid bioanalytical SRM LC-MS analysis of representative biological samples.

An evaluation of a four-channel multiplexed electrospray tandem mass spectrometry for higher throughput quantitative analysis

A four-channel multiplexed electrospray inlet system (MUX) coupled to a triple quadrupole mass spectrometer was investigated as a higher throughput approach to quantitative analysis. Four discrete samples may be simultaneously analyzed by virtue of a rotating sampler with a concomitant 4-fold increase in analytical throughput. Although absolute sensitivity was reduced using the MUX interface compared with analysis using traditional single electrospray interface, reproducibility of response was shown to be comparable. Source robustness was established for the analysis of both aqueous drug standards and drugs in biological media, and linearity of response for a test compound, diazepam, was demonstrated over 2 orders of magnitude. Analyte-dependent response differences were exhibited between the four channels of the interface, and this led to the overall conclusion that samples to be compared quantitatively must be analyzed through the same sprayer. In addition, each channel must be independently calibrated to afford true quantification. Should a deuterated internal standard be employed, however, quantitative comparisons can be made across channels. An HPLC pumping system providing individual back-pressure regulation to each channel was shown to provide adequate chromatography even in the event of a channel blockage. Furthermore, following multiple injections of biological samples onto the MUX interface, an eluent flow diversion was integrated into the first part of each analytical run. This served to prevent source fouling, and thus, no detrimental effects to response reproducibility or sensitivity were observed.

Capillary electrophoretic separation, immunochemical recognition and analysis of the diastereomers quinine and quinidine and two quinidine metabolites in body fluids

The capillary electrophoretic separation and immunochemical recognition of the two naturally fluorescing, cationic diastereomers quinine (QN) and quinidine (QD), their hydroderivatives and two major QD metabolites (3-hydroxyquinidine and quinidine-N-oxide) was investigated. Plain aqueous phosphate buffers and an alkaline buffer containing dodecyl sulfate micelles are shown to be incapable of resolving the two diastereomers. However, incorporation of an additional chemical equilibrium (with beta-cyclodextrin) in the case of capillary zone electrophoresis (CZE) and the presence of a small amount of an organic solvent as buffer modifier (2-propanol) in dodecyl sulfate based micellar electrokinetic capillary chromatography (MECC), were found to provide separation media which lead to complete resolution of QN, QD and the other compounds of interest. Furthermore, for MECC- and CZE-based immunoassay formats, a commercially available antibody against QD was found to be a perfect discriminator between QD and QN. It was determined to recognize QD and the two QD metabolites (cross reactivity of 20--30%) but not QN. MECC and CZE with laser induced fluorescence (LIF) detection are shown to be suitable to determine QD and metabolites in urine and plasma (quinidine-N-oxide only) collected after single dose intake of 50 mg QD sulfate and of QN in urine, saliva and serum samples that were collected after self-administration of 0.5 l of quinine water (25 mg of QN). With direct injection of a body fluid, MECC with LIF was found to provide 10 ng/ml detection limits for QD and QN. This ppb sensitivity is comparable to that obtained in HPLC assays that are based upon drug extraction. Furthermore, MECC and CZE assays with UV detection are shown to provide the ppm sensitivity required for therapeutic drug monitoring and clinical toxicology of QD and QN.

Quantitative determination of L-775,606, a selective 5-hydroxytryptamine 1D agonist, in rat plasma using automated sample preparation and detection by liquid chromatography-tandem mass spectrometry

L-775,606 is under investigation as a selective 5-hydroxytryptamine 1D agonist for the treatment of migraine. A reliable and sensitive method for the analysis of L-775,606 in plasma was required in order to support preclinical evaluation of this compound. A semi-automated sample preparation method using the Beckman Biomek 2000 workstation to perform all liquid handling tasks has been established. The sample analysis was performed using HPLC-MS-MS with a cycle time of 3.5 min per sample. Intra- and inter-day assay accuracy and precision are excellent with a calibration range of 1-2000 ng/ml and a reproducible limit of quantification of 1 ng/ml.

Selected reaction monitoring LC-MS determination of idoxifene and its pyrrolidinone metabolite in human plasma using robotic high-throughput, sequential sample injection

The generation of large numbers of samples during early drug discovery has increased the demand for rapid and selective methods of analysis. Liquid chromatography-tandem mass spectrometry (LC-MS-MS), because of its sensitivity, selectivity, and robustness, has emerged as a powerful tool in the pharmaceutical industry for many analytical needs. This work presents a high-throughput selected reaction monitoring LC-MS bioanalytical method for the determination of idoxifene, a selective estrogen receptor modulator, and its pyrrolidinone metabolite in clinical human plasma samples. The described method uses short, small-bore columns, high flow rates, and elevated HPLC column temperatures to perform LC separations of idoxifene and its metabolite within 10 s/sample. Sequential injections were accomplished with a 215/889 multiple probe liquid handler (Gilson, Inc.), which aspirates eight samples simultaneously and performs its rinse cycle parallel to sample injection, resulting in minimum lag time between injections. This high-throughput method was applied to the determination of idoxifene and its metabolite in clinical human plasma samples. Sample preparation employed liquid/liquid extraction in the 96-well format. Method validation included determination of intra- and interassay accuracy and precision values, recovery studies, autosampler stability, and freeze-thaw stability. The LOQ obtained was 10 ng/mL for idoxifene and 30 ng/mL for the metabolite. Using idoxifene-d5 as an internal standard, idoxifene showed acceptable accuracy and precision values at QC level 1 (QC1, 15 ng/mL), level 2 (QC2, 100 ng/mL), and level 3 (QC3, 180 ng/mL) (85.0% accuracy +/- 12.0% precision, 95.1 +/- 4.9%, and 90.3 +/- 4.7%, respectively). The pyrrolidinone metabolite also showed acceptable accuracy and precision values (using no internal standard for quantitation) at QC1 (60 ng/mL), QC2 (100 ng/mL), and QC3 (180 ng/mL) (104.9 +/- 14.4%, 91.1 +/- 13.0%, and 90.8 +/- 12.2%, respectively). The validated method was applied to the analysis of 613 human clinical plasma samples. An average run time of 23 s/sample (approximately 37 min/ 96-well plate or over 3,700 sample/day) was achieved. The successful validation presented indicates that rapid methods of analysis can efficiently and reliably contribute to the fast sample turnaround required for high sample number generating processes.

Higher throughput bioanalysis by automation of a protein precipitation assay using a 96-well format with detection by LC-MS/MS

Generic methodology for the automated preparation and analysis of drug levels in plasma samples within a drug discovery environment was achieved through the redesign of a protein precipitation assay to a microtiter (96-well) plate format and the application of robotic liquid handling for performance of all transfer and pipetting steps. Validation studies revealed that the application of robotics to sample preparation, in general, maintained the analytical accuracy and precision compared with preparing samples manually. The use of rapid gradient LC-MS/MS for analysis coupled with flow diversion of the solvent front allowed the introduction of protein-precipitated samples into the mass spectrometer without the necessity for source cleaning. The problem inherent in automatically pipetting plasma, caused by fibrinogen clots, was overcome by storing samples at -80 degrees C and thus precluding clot formation. The resulting methodology allowed sample preparation for a 96-well plate designed to accommodate 54 unknowns, duplicate 12-point calibration curves, and 6 sets of quality controls at three levels in approximately 2 h. This approach allowed an increase in throughput of sample preparation and analysis to >400 samples per day per LC-MS/MS instrument with minimal manual intervention. Overall, substantial time savings were realized, demonstrating that automation is an increasingly essential tool in a drug discovery bioanalytical environment.

Approaches to higher-throughput pharmacokinetics (HTPK) in drug discovery

With pressure on pharmaceutical companies to reduce time-to-market and improve the success rate of new drug candidates, higher-throughput pharmacokinetic (HTPK) support has become an integral part of many drug discovery programmes. This report details the amalgamation of robotics, new sample preparation technologies and highly sensitive and selective mass spectrometric detection systems to deliver the promise of HTPK. A historical perspective on automated bioanalysis with the current approaches and future prospects for the discipline are described.

Design and evaluation of an automated solid-phase extraction method development system for use with biological fluids

An automated solid-phase extraction method development system, utilizing a Zymate XP robot and a custom-designed solid-phase extraction manifold, has been developed and validated. This system spikes blank liquid matrix, such as plasma, with solutions containing drug, internal standard, and up to three metabolites. Samples are then buffered or diluted with an appropriate reagent. After these samples and corresponding blanks have been prepared, solid-phase cartridges containing selected sorbents are automatically conditioned. Samples are robotically vortexed and transferred to the conditioned cartridges, and analytes are extracted. Validation of this robotic system demonstrated acceptable precision and accuracy for three types of liquid transfer, including metering pump ( < 6% RSD and RE for > or = 2.0 mL dispensation), syringe-based laboratory station ( < or = 2.9% RSD and 0.5% RE for volumes between 0.25 and 1.00 mL), and syringe hands ( < 3.5% RSD and RE for volumes between 0.10 and 1.00 mL). For two example compounds, the system provided data which effectively distinguished good solid-phase sorbents from marginal ones through precision, recovery, and chromatographic selectivity. Solid-phase extraction of these compounds from human plasma gave precision (2-10% RSD) and extraction efficiency (96 +/- 6%) comparable to results obtained from manual extractions (92 +/- 11%).

High-performance liquid chromatographic determination of penicillins by means of automated solid-phase extraction and photochemical degradation with electrochemical detection

An automated precolumn exchange system for on-line solid-phase extraction (OPS-2) coupled to liquid chromatography with photochemical degradation and electrochemical detection was used for the determination of residual amounts of penicillin G, penicillin V, oxacillin, cloxacillin and dicloxacillin. A 5-10-fold increase in sensitivity was obtained when compared with direct UV detection of penicillins at 225 nm. The system is recommended for samples that have received an immunoaffinity clean-up. Analysis of bovine muscle tissue indicated, however, that this procedure could also be suitable for the determination of penicillin G at its maximum residue limit of 50 micrograms/kg even with conventional solvent partitioning for the first clean-up steps.