Genome-wide location analysis reveals an important overlap between the targets of the yeast transcriptional regulators Rds2 and Adr1

A simple and rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for the quantification of tetrahydrobiopterin (BH4) and dopamine in rat brain using epsilon-acetamidocaproic acid (AACA) as an internal standard. Proteins in the samples were precipitated with acetonitrile and then the supernatants were separated by a Sepax Polar-Imidazole (2.1 × 100 mm, i.d., 3 μm) column using a mixture of 10mM ammonium formate in acetonitrile/water (75:25, v/v) as the mobile phase at a flow rate of 300 μl/min. Quantification was performed on a triple quadrupole mass spectrometer employing electrospray ionization with the operating conditions as multiple reaction monitoring (MRM) and positive ion mode from m/z 242.1 → 166.0 for BH4, m/z 154.1 → 90.0 for dopamine and m/z 174.1 → 114.0 for AACA (IS). The total chromatographic run time was for 5.5 min. The method was validated for the analysis of samples: the limit of detection was 10 ng/g. The calibration curve was linear between 10-2000 ng/g for BH4 (r(2)=0.995) and 10-5000 ng/g for dopamine (r(2)=0.997) in the rat brain. Thus, good correlated LC-ESI/MS/MS results were obtained and found to be a powerful tool for the quantitative analysis of BH4 and dopamine in the rat brain.     

Sensitive and specific LC-ESI-MS/MS method for the determination of a styrylquinoline, BA011FZ041, a potent HIV anti-integrase agent, in rat plasma

A LC-MS/MS method was validated for the determination of BA011FZ041, a styrylquinoline derivative. After addition of BA011FZ055 as internal standard (IS), the method involved solid phase extraction (SPE), LC separation with an ether-phenyl column and quantification by MS/MS after positive ESI. The calibration curve, ranging from 1 to 500 ng/mL was fitted to a 1/x-weighted quadratic regression model. Lower limit of quantification (LLOQ) was 1 ng/mL using 100 microL of plasma. Intra- and inter-assay precision and accuracy values were within the regulatory limits. The method was successfully applied to the determination of BA011FZ041 in rat plasma and PBMCs after i.v. dosing.     

Liquid chromatography-tandem mass spectrometry assay for the quantitation of beta-dihydroartemisinin in rat plasma

Dihydroartemisinin (DHA) is a sesquiterpene used in the world as an antimalarial. To evaluate the pharmacokinetics of dihydroartemisinin in rats, a sensitive and specific liquid chromatography/tandem mass spectrometric (LC-MS/MS) method was developed and validated for the quantitation of dihydroartemisinin in rat plasma. For detection, a Sciex API 4000 LC-MS/MS with a TurboIonSpray ionization (ESI) inlet in the positive ion-multiple reaction monitoring (MRM) mode was used. The plasma samples were pre-treated by a simple liquid-liquid extraction with diethyl ether. The statistical evaluation for this method reveals excellent linearity, accuracy and precision for the range of concentrations 0.2-100.0 ng/mL. The method had a lower limit of quantification (LLOQ) of 0.2 ng/mL for beta-dihydroartemisinin in 100 microL of plasma. The method was successfully applied to the characterization of the pharmacokinetic profile of beta-dihydroartemisinin in rats after oral administration.     

Use of microbore LC-MS/MS for the quantification of oxcarbazepine and its active metabolite in rat brain microdialysis samples

A microbore LC-MS/MS method is developed and validated for the quantification of the anti-epileptic drug oxcarbazepine (OXC) and its active metabolite 10,11-dihydro-10-hydroxycarbamazepine (MHD) in rat brain microdialysates, together with the internal standard for microdialysis probe calibration, 2-methyl-5H-dibenz(b,f)azepine-5-carboxamide (m-CBZ). The benefits of gradient versus isocratic separation are shown, next to the improved sensitivity resulting from the addition of 0.1% formic acid to the mobile phase. The coupling of microdialysis with ESI-MS requires sample desalting for which column switching was applied. Using weighed regression to calculate the calibration curves (1-1000 ng/mL), the assay was validated in terms of linearity, accuracy and precision, yielding a sensitive (limit of quantification is 1 ng/mL) and selective method for quantification of OXC, MHD and m-CBZ. By applying this method, we were able to determine the extracellular concentrations of OXC and MHD during at least 4h after intraperitoneal (i.p.) administration of 10 mg/kg OXC.     

A rapid, sensitive and selective liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry method for determination of fenretinide (4-HPR) in plasma

A simple and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method using an atmospheric pressure chemical ionization source (APCI) for the quantification of fenretinide (4-HPR) in mouse plasma was developed and validated. After a simple protein precipitation of plasma sample by acetonitrile, 4-HPR was analyzed by LC-APCI-MS/MS. High-performance liquid chromatography (HPLC) separation was conducted on a Hypurity C18 column (50mmx2.1mm, 5microm) with a flow rate 0.60mL/min using a gradient mobile phase comprised of 0.05% formic acid in water (A) and methanol (B), and a run time of 4.5min. The elimination of a tedious sample preparation process and a shorter run time substantially reduced total analysis time. The method was linear over the range 0.5-100ng/mL, with r>0.998. The intra- and inter-assay precisions were 1.4-9.2% and 5.1-8.2%, respectively, and the intra- and inter-assay accuracies were 93.9-98.6% and 92.7-95.3%, respectively. The absolute recoveries were 90.3% (1.5ng/mL), 97.0% (7.5ng/mL) and 92.1% (75.0ng/mL) for 4-HPR, and 99.1% for the internal standard (150ng/mL). The analytical method had excellent sensitivity using a small sample volume (30microL) with the lower limit of quantification (LLOQ) 0.5ng/mL. This method is robust and has been successfully employed in a pharmacokinetic study of 4-HPR in a mouse xenograft model of neuroblastoma.     

Quantification of 3-deazaneplanocin A, a novel epigenetic anticancer agent, in rat biosamples by hydrophilic interaction liquid chromatography-tandem mass spectrometric detection

A sensitive and selective LC-MS/MS based bioanalytical method was developed and validated for the quantification of 3-deazaneplanocin A (DZNep), a novel epigenetic anti-tumor drug candidate, in Sprague-Dawley (SD) rat biosamples (plasma, urine, feces and tissue samples). The method comprises a phenylboronic acid (PBA)-containing solid phase extraction procedure, serving for binding and clean-up of DZNep in rat biosamples spiked with tubercidin (as internal standard). The analytes were separated on an Agilent hydrophilic interaction chromatography (HILIC) column. LC-MS/MS in positive ion mode was used to perform multiple reaction monitoring at m/z of 263/135 and 267/135 for DZNep and tubercidin, respectively. The limit of quantification (LOQ) of DZNep in rat biosamples was 20 ng/mL. The data of intra-day and inter-day accuracy were within 15% of nominal concentration while the precision (relative standard deviation) less than 10% for all biosamples. The extraction recoveries for DZNep and tubercidin were consistent and reproducible (around 80%) and the matrix effects were negligible (around 10% suppression) in all biosamples. This method was demonstrated to be applicable for pharmacokinetic studies of DZNep in SD rats.     

Simultaneous quantification of nicotine and metabolites in rat brain by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous quantification of nicotine (NIC), cotinine (COT), nornicotine (NNIC), norcotinine (NCOT), nicotine-N-β-D-glucuronide (NIC GLUC), cotinine-N-β-D-glucuronide (COT GLUC), nicotine-1'-oxide (NNO), cotinine-N-oxide (CNO), trans-3'-hydroxycotinine (3-HC), anabasine (AB) and anatabine (AT) was modified and validated for quantification of these selected analytes in rat brain tissue. This analytical method provides support for preclinical NIC pharmacokinetic and toxicological studies after controlled dosing protocols. After brain homogenization and solid-phase extraction, target analytes and corresponding deuterated internal standards were chromatographically separated on a Discovery(?) HS F5 HPLC column with gradient elution and analyzed by LC-MS/MS in positive electrospray ionization (ESI) mode with multiple reaction monitoring (MRM) data acquisition. Method linearity was assessed and calibration curves were determined over the following ranges: 0.1-7.5 ng/mg for NIC, COT GLUC and AB; and 0.025-7.5 ng/mg for COT, NNIC, NCOT, NIC GLUC, NNO, CNO, 3-HC and AT (R(2)≥0.99 for all analytes). Extraction recoveries ranged from 64% to 115%, LC-MS/MS matrix effects were ≤21%, and overall process efficiency ranged from 57% to 93% at low and high quality control concentrations. Intra- and inter-assay imprecisions and accuracy for all analytes were ≤12.9% and ≥86%, respectively. The method was successfully applied to quantification of NIC and metabolites in the brain of post-natal day 90 rats that were sacrificed 2-h after a single 0.8 mg/kg s.c. administration of (-)NIC. In these tissues, striatal concentrations were 204.8±49.4, 138.2±14.2 and 36.1±6.1 pg/mg of NIC, COT and NNIC, respectively. Concentrations of NIC, COT and NNIC in the remaining whole brain (RWhB) were 183.3±68.0, 130.0±14.1 and 46.7±10.3 pg/mg, respectively. Quantification of these same analytes in plasma was also performed by a previously validated method. NIC, COT, NNIC, NCOT, NNO and CNO were detected in plasma with concentrations comparable to those reported in previous studies. However, and in contrast to brain tissues, COT concentrations in plasma were significantly higher than were those of NIC (194.6±18.6 ng/mL versus 52.7±12.9 ng/mL). Taken together, these results demonstrate that a sensitive and selective method has been developed for the determination of NIC biomarkers in rat brain.     

Quantification of fluorotelomer-based chemicals in mammalian matrices by monitoring perfluoroalkyl chain fragments with GC/MS

Perfluorocarboxylic acids (PFCAs), namely perfluorooctanoic acid (PFOA) and perfluorononanoic acid (PFNA), have been identified as persistent, bioaccumulative and potentially toxic compounds. The structural analog, 8-2 fluorotelomer alcohol (8-2 fTOH) is considered the probable precursor of these stable metabolites. Because simultaneous quantification is needed for volatile and non-volatile perfluorinated chemicals (PFCs) in complex matrices, a GC/MS method was developed and tested based on selected ion monitoring of perfluorinated alkyl parent chain fragment ions. Although the method requires a derivatization step, combined GC/MS analysis of PFCA-me's and FTOHs increases analytical efficiency and decreases sample analysis time. The method instrument detection limits are between 7.1 and 24.5 ng/mL extract (MTBE), and the method quantification limits are below 50 ng/mL serum or ng/g liver for all PFCs investigated. Recoveries from mouse serum and liver homogenates, which were spiked with FTOHs and PFCAs at levels of 25 and 200 ng/mL or ng/g, ranged from 81 to 101%. Finally, the utility of the method was demonstrated by dosing male CD-1 mice with 30 mg/kg-BW of 8-2 fTOH and quantifying PFCs 6h post-treatment. The advantages of this method are (1) the simultaneous detection of both volatile and non-volatile fluorotelomer-based chemicals in complex matrices, such as mammalian tissues, (2) as a confirmatory method to LC-MS/MS, and (3) as an alternative method of analysis for laboratories without access to LC-MS/MS.     

Determination of amiodarone and desethylamiodarone in horse plasma and urine by high-performance liquid chromatography combined with UV detection and electrospray ionization mass spectrometry

A rapid method for the quantification of amiodarone and desethylamiodarone in animal plasma using high-performance liquid chromatography combined with UV detection (HPLC-UV) is presented. The sample preparation includes a simple deproteinisation step with acetonitrile. In addition, a sensitive method for the quantification of amiodarone and desethylamiodarone in horse plasma and urine using high-performance liquid chromatography combined with electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) is described. The sample preparation includes a solid-phase extraction (SPE) with a SCX column. Tamoxifen is used as an internal standard for both chromatographic methods. Chromatographic separation is achieved on an ODS Hypersil column using isocratic elution with 0.01% diethylamine and acetonitrile as mobile phase for the HPLC-UV method and with 0.1% formic acid and acetonitrile as mobile phase for the LC-MS/MS method. For the HPLC-UV method, good linearity was observed in the range 0-5 microg ml(-1), and in the range 0-1 microg ml(-1) for the LC-MS/MS method. The limit of quantification (LOQ) was set at 50 and 5 ng ml(-1) for the HPLC-UV method and the LC-MS/MS method, respectively. For the UV method, the limit of detection (LOD) was 15 and 10 ng ml(-1) for amiodarone and desethylamiodarone, respectively. The LODs of the LC-MS/MS method in plasma were much lower, i.e. 0.10 and 0.04 ng ml(-1) for amiodarone and desethylamiodarone, respectively. The LODs obtained for the urine samples were 0.16 and 0.09 ng ml(-1) for amiodarone and desethylamiodarone, respectively. The methods were shown to be of use in horses. The rapid HPLC-UV method was used for therapeutic drug monitoring after amiodarone treatment, while the LC-MS/MS method showed its applicability for single dose pharmacokinetic studies.     

A rapid and sensitive LC-MS/MS assay for the quantitation of deacetyl mycoepoxydiene in rat plasma with application to preclinical pharmacokinetics studies

The purpose of this study was to develop and validate a high-performance liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method for analysis of the deacetyl mycoepoxydiene in rat plasma. The analyte and internal standard (I.S.), benorilate, were extracted from rat plasma by precipitation protein and separated on a C(18) column using acetonitrile-0.5% formic acid as mobile phase. Detection was performed using a turbo-spray ionization source and mass spectrometric positive multi-reaction-monitoring-mode (+MRM) at an ion voltage of +4800 V. The assay was linear over the concentration range 5-5000 ng/mL with the lowest limit of quantification (LLOQ) of 5 ng/mL. The method also afforded satisfactory results in terms of the sensitivity, specificity, precision (intra- and inter-day, RSD<5.8%), accuracy, recovery as well as the stability of the analyte under various conditions. The method was successfully applied to a preclinical pharmacokinetic study in rats after a single intravenous administration of deacetyl mycoepoxydiene 10 mg/kg.     

A highly sensitive assay for ritodrine in human serum by hydrophilic interaction chromatography-tandem mass spectrometry

We developed a sensitive assay for ritodrine (RTD), a beta2-adrenergic agonist, in human serum. This method was based upon the selective and sensitive technique by a tandem mass spectrometry (MS/MS) using a hydrophilic interaction chromatography (HILIC) technique. This method involved a mixed-mode cation-exchange solid-phase extraction of RTD and isoxsuprine, the internal standard (IS), from serum with Waters Oasis MCX cartridges. The detection was made using a Micromass Quattromicro API LC-MS/MS system with electrospray ionization source in positive ion mode. The separation of the analytes was achieved within 4 min on a silica column with a mobile phase of ammonium acetate (10 mM, pH 4.5) and acetonitrile (10:90, v/v). Multiple reaction monitoring was utilized by monitoring 288.2-->121.1 for RTD, 302.2-->107.0 for IS. The calibration curve for RTD was linear over a range of 0.5-1000 ng/mL. When 50 microL serum was used for extraction, the lower limit of quantification was 0.39 ng/mL (97.5 fg on-column). The percent coefficient of validation for accuracy and precision (inter- and intra-day) was less than 9.8% and the recovery was ranged from 83.5 to 94.7% for RTD. This method enabled us to successfully determine RTD in maternal and fetal sera.     

Quantitative determination of cyclic polylactic acid oligomers in serum by direct injection liquid chromatography tandem mass spectrometry

Polylactic acid (PLA) is a biodegradable polymer, currently used in pharmaceutical and surgical devices. There is a concern that cyclic polylactic acid (CPLA), which is a by-product of PLA synthesis, may be introduced into the human body as an undesirable contaminant. We carried out a quantitation investigation of the CPLA heptamer (CPLA-7) by liquid chromatography mass spectrometry (LC-MS). We found that CPLA-7 binds strongly with serum proteins and that only 62% of CPLA-7 was recovered after routine deproteination; therefore, we directly injected serum into the LC-MS/MS system after passage through a bovine serum albumin (BSA)-coated chromatographic column and found the recovery of CPLA-7 was improved to 84%, and that the detection (S/N=3) and quantitation limit (S/N=10 and below 15% relative standard deviation) were 1.5 and 2.5 ng/mL, respectively. We conclude that direct injection LC-MS/MS, using a BSA column, is a simple and effective quantitative analysis method for CPLA in serum.     

Sensitive and rapid liquid chromatography/tandem mass spectrometric assay for the quantification of chloroquine in dog plasma

A simple, sensitive and rapid liquid chromatography/tandem mass spectrometric (LC-MS/MS) method was developed and validated for quantification of chloroquine, an antimalarial drug, in plasma using its structural analogue, piperazine bis chloroquinoline as internal standard (IS). The method is based on simple protein precipitation with methanol followed by a rapid isocratic elution with 10 mM ammonium acetate buffer/methanol (25/75, v/v, pH 4.6) on Chromolith SpeedROD RP-18e reversed phase chromatographic column and subsequent analysis by mass spectrometry in the multiple reaction monitoring mode (MRM). The precursor to product ion transitions of m/z 320.3-->247.2 and m/z 409.1-->205.2 were used to measure the analyte and the IS, respectively. The assay exhibited a linear dynamic range of 2.0-489.1 ng/mL for chloroquine in dog plasma. The limit of detection (LOD) and lower limit of quantification (LLOQ) were 0.4 and 2.0 ng/mL, respectively in 0.05 mL plasma. Acceptable precision and accuracy were obtained for concentrations over the standard curve range of 2.0-489.1 ng/mL. A run time of 2.0 min for a sample made it possible to achieve a throughput of more than 400 plasma samples analyzed per day. The validated method was successfully used to analyze samples of dog plasma during non-clinical study of chloroquine.     

Sensitive and selective liquid chromatography-tandem mass spectrometry method for the quantification of aniracetam in human plasma

A rapid, sensitive and selective LC-MS/MS method was developed and validated for the quantification of aniracetam in human plasma using estazolam as internal standard (IS). Following liquid-liquid extraction, the analytes were separated using a mobile phase of methanol-water (60:40, v/v) on a reverse phase C18 column and analyzed by a triple-quadrupole mass spectrometer in the selected reaction monitoring (SRM) mode using the respective [M+H]+ ions, m/z 220-->135 for aniracetam and m/z 295-->205 for the IS. The assay exhibited a linear dynamic range of 0.2-100 ng/mL for aniracetam in human plasma. The lower limit of quantification (LLOQ) was 0.2 ng/mL with a relative standard deviation of less than 15%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The validated LC-MS/MS method has been successfully applied to study the pharmacokinetics of aniracetam in healthy male Chinese volunteers.     

Determination of rimonabant in human plasma and hair by liquid chromatography-mass spectrometry

Rimonabant is the first therapeutically relevant cannabinoid antagonist, licensed in Europe for treatment of obesity when a risk factor is associated. The objective of this study was to develop and validate a method for measurement of rimonabant in human plasma and hair using liquid chromatography coupled to mass spectrometry (LC-MS/MS). Rimonabant and AM-251 (internal standard) were extracted from 50muL of plasma or 10mg of hair using diethylether. Chromatography was performed on a 150mmx2.1mm C18 column using a mobile phase constituted of formate buffer/acetonitrile. Rimonabant was ionized by electrospray in positive mode, followed by detection with mass spectrometry. Data were collected either in full-scan MS or in full-scan MS/MS mode, selecting the ion m/z 463.1 for rimonabant and m/z 555.1 for IS. The most intense product ion of rimonabant (m/z 380.9) and IS (m/z 472.8) were used for quantification. Calibration curves covered a range from 2.5 (lower limit of quantification) to 1000.0ng/mL (upper limit of quantification) in plasma and from 2.5 to 1000.0pg/mg in hair. Validation results demonstrated that rimonabant could be accurately and precisely quantified in both matrixes: accuracy and precision were within 85-115% and within 15% of standard deviation, respectively. Stability studies in plasma showed that rimonabant was stable during the assay procedure, but a 30% decrease was observed for one concentration after 3 weeks at -20 degrees C. This simple and robust LC-MS/MS method can be used for measuring rimonabant concentrations in human plasma and hair either in clinical or in forensic toxicology.     

Highly sensitive quantification of key regulatory oxysterols in biological samples by LC-ESI-MS/MS

We describe a highly sensitive and specific method for the quantification of key regulatory oxysterols in biological samples. This method is based upon a stable isotope dilution technique by liquid chromatography-tandem mass spectrometry (LC-MS/MS). After alkaline hydrolysis of human serum (5 microl) or rat liver microsomes (1 mg protein), oxysterols were extracted, derivatized into picolinyl esters, and analyzed by LC-MS/MS using the electrospray ionization mode. The detection limits of the picolinyl esters of 4beta-hydroxycholesterol, 7alpha-hydroxycholesterol, 22R-hydroxycholesterol, 24S-hydroxycholesterol, 25-hydroxycholesterol, 27-hydroxycholesterol, and 24S,25-epoxycholesterol were 2-10 fg (5-25 amol) on-column (signal-to-noise ratio = 3). Reproducibilities and recoveries of these oxysterols were validated according to one-way layout and polynomial equation, respectively. The variances between sample preparations and between measurements by this method were calculated to be 1.8% to 12.7% and 2.9% to 11.9%, respectively. The recovery experiments were performed using rat liver microsomes spiked with 0.05 ng to 12 ng of oxysterols, and recoveries of the oxysterols ranged from 86.7% to 107.3%, with a mean recovery of 100.6%. This method provides reproducible and reliable results for the quantification of oxysterols in small amounts of biological samples.     

Development and validation of a rapid 96-well format based liquid-liquid extraction and liquid chromatography-tandem mass spectrometry analysis method for ondansetron in human plasma

A rapid and sensitive LC-MS/MS method for the quantification of ondansetron was developed and validated. The plasma samples were treated by a semi-automated liquid-liquid extraction (LLE) in 1.2 mL 96-well format micro-tubes. Ondansetron and the internal standard (IS) granisetron were analyzed by combined reversed phase LC-MS/MS, with positive ion electrospray ionization, using multiple reactions monitoring (MRM). The statistical evaluation for this method reveals excellent linearity, accuracy and precision values for the range of concentrations 0.25-40.0 ng/mL. The proposed method enabled the reliable determination of ondansetron in bioequivalence studies after per os administration of a 4 or 8 mg tablet.     

A rapid and sensitive HPLC-MS/MS analysis and preliminary pharmacokinetic characterization of sibiricaxanthone F in rats

A simple, rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for quantifying sibiricaxanthone F (SF) in rat plasma following oral and intravenous dosings. After addition of the internal standard (IS) kaempferol and the antioxidant, 20% ascorbic acid, plasma samples were precipitated with acetonitrile and separated on an Aglient Zorbax XDB-C(18) column (50 mm × 4.6mm I.D., 2.1 μm) with gradient acetonitrile and water (both containing 0.01% formic acid) as the mobile phase. The detection was performed on a Sciex API 4000 LC-MS/MS with electrospray ionization (ESI) inlet in the negative multiple reaction monitoring (MRM) mode. Good linearity was achieved over the concentration range of 0.5-500.0ng/mL (r>0.996). Intra- and inter-day precisions were less than 7.60%, and accuracy ranged from 97.18% to 99.84%. The lower limit of quantification for SF was 0.5 ng/mL, and analytes were stable under various conditions (during freeze-thaw, at room temperature and under deep-freeze conditions). This validated method was successfully applied to the preliminary pharmacokinetic study of SF in rats for the first time, and the absolute bioavailability of SF was found to be only 0.22 ± 0.15%.     

Quantitative analysis of thymosin alpha1 in human serum by LC-MS/MS

A high performance liquid chromatography with tandem mass spectrometry (LC-MS/MS) method was developed to measure the thymosin alpha 1 (Talpha1) concentration in human serum. Tá1 in human serum was determined by solid phase extraction and reverse phase LC-MS/MS. The high-performance liquid chromatography (HPLC) system interfaced with the MS/MS system with a Turbo Ion spray interface. Positive ion detection and multiple reaction monitoring (MRM) mode were used for this human serum quantitation. Eight different concentration standards were used to establish the detection range. Six quality control (QC) and 2 matrix blanks were checked by calibration curves performed on the same day. The lower quantitation limit was 0.5 ng/mL Talpha1 in human serum. Calibration curves were established between 0.5 to 100 ng/mL by weighted linear regression. The correlation coefficients for different days were 0.9955 or greater. Quantitation of Talpha1 by the LC-MS/MS method is fast, accurate, and precise.     

Development of a liquid chromatography-mass spectrometry (LC/MS) assay method for the quantification of PSC 833 (Valspodar) in rat plasma

A liquid chromatography-mass spectrometry (LC/MS) assay method was developed for the quantification of PSC 833 in rat plasma, using amiodarone as internal standard (IS). Separation was achieved using a C(8) 3.5 microm (2.1 mm x 50 mm) column heated to 60 degrees C with a mobile phase consisting of acetonitrile-ammonium hydroxide 0.2% (90:10 v/v) pumped at a rate of 0.2 mL/min. Detection was accomplished by mass spectrometer using selected ion monitoring (SIM) in positive mode. An excellent linear relationship was present between peak height ratios and rat plasma concentrations of PSC 833 ranging from 10 to 5000 ng/mL (R(2)>0.99). Intra-day and inter-day coefficients of variation (CV%) were less than 15%, and mean error was less than 10% for the concentrations above the limit of quantification. The validated limit of quantification of the assay was 10 ng/mL based on 0.1 mL rat plasma. The method limit of detection, based on an average signal-to-noise (S/N) ratio of 3, was found to be 2.5 ng/mL. The assay was capable of measuring the plasma concentrations of PSC 833 in rats injected with a single dose of 5 mg/kg of the drug. PSC 833 and IS eluted within 4 min, free of interfering peaks. The method was found to be fast, sensitive, and specific for the quantification of PSC 833 in rat plasma.