Determination of caudatin-2,6-dideoxy-3-O-methy-beta-d-cymaropyranoside in rat plasma using liquid chromatography-tandem mass spectrometry

A selective, sensitive and rapid liquid chromatography-tandem mass spectrometry method has been developed for the determination of caudatin-2,6-dideoxy-3-O-methy-beta-d-cymaropyranoside (CDMC) in rat plasma. This method involves a plasma clean-up step using liquid-liquid extraction, followed by LC separation and positive electrospray ionization mass spectrometry detection (LC/ESI-MS/MS). Chromatographic separation of the analytes was achieved using a C(18) column with a mobile phase of acetonitrile and water (70:30, v/v) at a flow rate of 1.0 mL/min. Low energy collision tandem mass spectrometric analysis (CID-MS/MS) using the multiple reaction monitoring (MRM) mode was used for analyte quantification. For the MRM analysis of CDMC, the following transition at m/z 658.4 --> 529.6 derived from the protonated molecule [M + Na](+). A calibration curve was linear in the 5-500 ng/mL range for CDMC, and the limit of detection was 5 ng/mL. The inter- and intra-day precisions (RSD) were 相似文献   

Simultaneous determination of atractylenolide II and atractylenolide III by liquid chromatography-tandem mass spectrometry in rat plasma and its application in a pharmacokinetic study after oral administration of Atractylodes Macrocephala Rhizoma extract

Atractylenolide II (AII) and atractylenolide III (AIII) are the major active components in Atractylodes Macrocephala Rhizoma (AMR). In this study, a sensitive, rapid and selective liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed and validated for the simultaneous determination of AII and AIII in rat plasma using loliolide as internal standard (IS). After protein precipitation with ethyl acetate, the analytes were injected into an LC‐MS/MS system for quantification. Chromatography was performed using a C₁₈ column, eluting with water and acetonitrile (45:55, v/v) at 0.2 mL/min. All analytes including IS were monitored under positive ionization conditions by multiple reaction monitoring with an electrospray ionization source. The validated method was successfully applied to the pharmacokinetic study of AII and AIII in rat plasma after oral administration of AMR extract. The results provided a meaningful basis for evaluating the clinical applications of traditional Chinese medicine. Copyright © 2012 John Wiley & Sons, Ltd.     

Study of tanshinone IIA tissue distribution in rat by liquid chromatography-tandem mass spectrometry method

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and validated for determining tanshinone IIA in rat tissues. After a single step liquid-liquid extraction with diethyl ether, tanshinone IIA and loratadine (internal standard) was subjected to LC/MS/MS analysis using positive electro-spray ionization under selected reaction monitoring mode. Chromatographic separation of tanshinone IIA and loratadine was achieved on a Hypersil BDS C(18) column (i.d. 2.1 x 50 mm, 5 microm) with a mobile phase consisting of methanol-1% formic acid (90:10, v/v) at a flow rate of 300 microL/min. The intra-day and inter-day precision of the method were less than 10.2 and 12.4%, respectively. The intra-day and inter-day accuracies ranged from 99.7 to 109.7%. The lowest limit of quantification for tanshinone IIA was 1 ng/mL. The method was applied to a tanshinone IIA tissue distribution study after an oral dose of 60 mg/kg to rats. Tanshinone IIA tissue concentrations decreased in the order of stomach > small intestine > lung > liver > fat > muscle > kidneys > spleen > heart > plasma > brain > testes. Tanshinone IIA still could be detected in most of the tissues at 20 h post-dosing. These results indicate that the LC/MS/MS method was rapid and sensitive to quantify tanshinone IIA in different rat tissues.     

Simultaneous determination of tanshinone IIA and its three hydroxylated metabolites by liquid chromatography/tandem mass spectrometry

A rapid and sensitive method based on liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the simultaneous determination of tanshinone IIA and its three hydroxylated metabolites, tanshinone IIB, hydroxytanshinone IIA and przewaquinone A, in a rat liver microsome was developed and fully validated. A single step of liquid-liquid extraction with ethyl acetate was utilized in this method. Chromatographic separation of the sample matrix from the analytes and the internal standard diazepam was performed using a Shim-pack VP-ODS analytical column. Detection was performed on a triple quadrupole tandem mass spectrometer equipped with an electrospray ionization source and operated in selected reaction monitoring (SRM) mode. The method was linear in the concentration range of 1-500 ng/mL for all analytes. The intra- and inter-day precisions (RSD %) were within 15% and deviations of the assay accuracies were within 15.0% for all analytes. The analytes proved to be stable during sample storage, preparation and analyses. This validated method was successfully applied to the enzyme kinetic study of tanshinone IIA in liver microsome. The elimination of tanshinone IIA and formation of tanshinone IIB and hydroxytanshinone IIA in the liver microsome all exhibited a sigmoidal kinetics profile. The formation of przewaquinone A shows a typical hyperbolic profile. In addition, this method has now been applied in the analysis of other bio-samples including plasma, urine, bile and feces.     

Different quantitation approaches for xenobiotics in human urine samples by liquid chromatography/electrospray tandem mass spectrometry

The potential of liquid chromatography combined with tandem mass spectrometry (LC/MS/MS) for the determination of pesticide metabolites in human urine at the sub-ppb level is explored. Metabolites from two organophosphorous pesticides, 4-nitrophenol (from parathion and parathion-methyl) and 3-methyl-4-nitrophenol (from fenitrothion), are taken as model analytes to conduct this study. After direct injection of the urine sample (10 microL), different approaches were evaluated in order to achieve correct quantitation of analytes using an electrospray ionisation (ESI) interface. Thus, the feasibility of using external calibration was checked versus the use of different isotope-labeled internal standards. The advantages of applying coupled-column liquid chromatography (LC/LC) as an efficient clean-up without any type of sample manipulation are also discussed. The combination of LC/LC with ESI-MS/MS allows the direct analysis of free metabolites in urine, as the automated clean-up performed by the coupled-column technique is sufficient for the removal of interferences that suppress the ionisation of analytes in the ESI source. Using this procedure with external calibration, good precision and recoveries, and detection limits below 1 ng/mL are reached with analysis run times of around 8 min. The hyphenated technique LC/LC/ESI-MS/MS is proved to be a powerful analytical tool, allowing the rapid, sensitive and selective determination of 4-nitrophenol and 3-methyl-4-nitrophenol in human urine without any sample treatment.     

An accurate and reproducible method for the quantitative analysis of isoflavones and their metabolites in rat plasma using liquid chromatography/mass spectrometry combined with photodiode array detection

To study the safety and potential health benefits of soy isoflavones, a rapid and simple method based on liquid chromatography combined with mass spectrometry (LC/MS) and photodiode array detector (PDA) was developed for the determination of isoflavones in rat plasma. The analytes included daidzein, genistein, glycitein, equol, 4-ethyl phenol, and biochanin A over a concentration range of 1.0-4320.0 nM using 75 microL of rat plasma. Rat plasma samples were hydrolyzed by adding an enzyme mixture from Helix pomatia containing glucuronidase and sulfatase to convert the isoflavone beta-glycosides daidzin, genistin, and glycitin to their active aglycone forms. A liquid-liquid extraction method using ethyl acetate as the extraction solvent was used to extract aglycones and the internal standards (phenolphthalein beta-D glucuronide, 4-methylumbelliferyl sulfate, and apigenin) from digested plasma samples. The extract was evaporated to dryness under a nitrogen stream, reconstituted with 0.1% formic acid in water-acetonitrile (85 + 15), and injected into a Zorbax SB-CN reversed-phase column (4.6 x 75 mm, 3.5 microm particle size). The Micromass ZQ detector was operated in the positive ion selected-ion monitoring mode. The flow rate for LC was 1.0 mL/min, with a split where 25% of the effluent was introduced into the electrospray ionization probe of the MS instrument and 75% into the PDA. The chromatographic run time was 16.0 min, with delay of 10 min/injection. The interday precision and accuracy of the standard samples were <2.6% relative standard deviation and <10% relative error, respectively. Recovery of the reported isoflavones with this method varied from 86 to 100%.     

Capillary liquid chromatography-tandem mass spectrometry of tetrahydroisoquinoline derived neurotoxins: a study on the blood-brain barrier of rat brain

Certain tetrahydroisoquinoline derivatives such as 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1-BnTIQ) and N-methylsalsolinol are parkinsonian neurotoxins. This paper describes a sensitive and reliable analytical method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the determination of tetrahydroisoquinoline derivatives (TIQs) in brain dialysate. Samples (20 microL injected) were effectively stacked and cleaned up in-line on a capillary column (5 cm x 0.25 mm I.D.) packed with 5 microm phenyl reversed-phase silica particles. Under the optimized conditions, electrospray ionisation-MS/MS detection of TIQs was highly sensitive. The capillary LC-MS/MS method had a detection limit of 2 ng/ml for TIQ. The method was used in combination with in vivo microdialysis to study the blood-brain barrier (BBB) for TIQs. The microdialysis probe was implanted in the frontal cortex of rat brain. Test compounds were administered intraperitoneally (i.p.). Four TIQs including 1,2,3,4-tetrahydroisoquinoline (TIQ), 5,6,7,8-tetrahydroisoquinoline (5-TIQ), 1-BnTIQ, and salsolinol (SAL) were studied. A concentration maximum was detected in brain dialysate for TIQ, 5-TIQ, and 1-BnTIQ about 40 min after drug administration. However, SAL, the precursor of N-methylsalsolinol was found unable to cross the BBB of rat brain.     

Simultaneous determination of docetaxel and ketoconazole in rat plasma by liquid chromatography/electrospray ionization tandem mass spectrometry

A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for simultaneous quantification of docetaxel and ketoconazole in rat plasma with paclitaxel as internal standard (IS). The analytes were extracted from rat plasma by using a liquid-liquid extraction technique with ethyl acetate and the LC separation was performed on a Cosmosil-C(18) analytical column (150 mm x 2.0 mm i.d., Nacalai Tesque Inc., Japan). The extracted samples were analyzed with LC/MS/MS, operating in selected reaction monitoring (SRM) mode. The SRM transitions of precursor ions to product ions were 830.3-->549.1 (m/z) for docetaxel, 531.2-->489.3 (m/z) for ketoconazole, and 876.7-->307.9 (m/z) for the IS. The calibration curves were linear over the range of 2-500 ng/mL for docetaxel and 50-20 000 ng/mL for ketoconazole, with coefficients of correlation above 0.999. The limits of quantification for docetaxel and ketoconazole were both 2 ng/mL. The limit of detection for each analyte was 1 ng/mL. The intra- and inter-day precision (CV) of analysis were within 7%, and the accuracy ranged from 95 to 110%. The overall recoveries for docetaxel and ketoconazole were about 89.0% and 91.1%, respectively. The total analysis time was only 9.0 min. This quantitation method was successfully applied to the simultaneous determination of docetaxel and ketoconazole in rat plasma and some potential interaction was found in the current coadministration pharmacokinetic study. This established method was also utilized in the in vitro and in vivo drug-drug interaction study of docetaxel and ketoconazole (to be published).     

Quantitative determination of buprenorphine,naloxone and their metabolites in rat plasma using hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry

A rapid and sensitive LC–MS/MS method was developed and validated for the simultaneous determination of buprenorphine and its three metabolites (buprenorphine glucuronide, norbuprenorphine and norbuprenorphine glucuronide) as well as naloxone and its metabolite naloxone glucuronide in the rat plasma. A hydrophilic interaction chromatography column and a mobile phase containing acetonitrile and ammonium formate buffer (pH 3.5) were used for the chromatographic separation. Mass spectrometric detection was achieved by an electrospray ionization source in the positive mode coupled to a triple quadrupole mass analyzer. The calibration curves for the six analytes displayed good linearity over the concentration range 1.0 or 5.0–1000 ng/mL. The intra and inter‐day precision (CV) ranged from 2.68 to 16.4% and from 9.02 to 14.5%, respectively. The intra‐ and inter‐day accuracy (bias) ranged from −14.2 to 15.2% and from −9.00 to 4.80%, respectively. The extraction recoveries for all the analytes ranged from 55 to 86.9%. The LC–MS/MS method was successfully applied to a pharmacokinetic study of buprenorphine–naloxone combination in rats.     

Quantification of dexamethasone and corticosterone in rat biofluids and fetal tissue using highly sensitive analytical methods: assay validation and application to a pharmacokinetic study

A sensitive, specific, accurate and precise LC/MS/MS method was developed for the simultaneous measurement of dexamethasone and corticosterone in rat plasma. The method was extended to dexamethasone analysis in rat plasma ultrafiltrate and fetal tissues. Samples were processed using SPE involving Oasis HLB cartridges, which offered complete extraction recovery for the analytes. Samples were subsequently analyzed using LC/MS/MS. A structurally related corticosteroid, prednisolone, was used as the internal standard. Using a 500 microL plasma sample, limits of quantification of 0.2 and 2.0 ng/mL were achievable for dexamethasone and corticosterone. This level of sensitivity allowed characterization of maternal/fetal dexamethasone profiles after administration of multiple doses of dexamethasone sodium phosphate to rats. However, this sensitivity was not satisfactory for corticosterone during pharmacokinetic studies involving dexamethasone due to its strong adrenosuppressive effect. This led us to investigate the suitability of a commercially available radioimmunoassay kit, which through extensive testing and minor modifications was found to offer extremely sensitive, specific, accurate and precise analysis of corticosterone. Knowledge of the steroid profiles captured using these highly sensitive analytical tools may potentially help in the optimization of corticosteroid therapy during pregnancy.     

Quantification of docetaxel and its main metabolites in human plasma by liquid chromatography/tandem mass spectrometry

Docetaxel is an antineoplastic agent widely used in therapeutics. The objective of this study was to develop and validate a routine assay, using liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS), for the simultaneous quantification of docetaxel and its main hydroxylated metabolites in human plasma. A structural analogue, paclitaxel, was used as the internal standard. Determination of docetaxel and four metabolites (M1, M2, M3 and M4) was achieved using only 100 microL of plasma. Liquid-liquid extraction was used for sample preparation, with extraction efficiency of at least 90% for all analytes. Detection used positive-mode electrospray ionization in selected reaction monitoring mode. The lower limit of quantification (LLOQ) was 0.5 ng/mL for all analytes. The assay was linear in the calibration curve range 0.5-1000 ng/mL and acceptable precision and accuracy (<15%) were obtained with concentrations above the LLOQ. This method was sufficiently selective and sensitive for quantification of metabolites in plasma from cancer patients receiving docetaxel chemotherapy, and is suitable for routine analyses during pharmacokinetic studies.     

Separation of a BMS drug candidate and acyl glucuronide from seven glucuronide positional isomers in rat plasma via high-performance liquid chromatography with tandem mass spectrometric detection

A high-performance liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for the determination of a BMS drug candidate and its acyl glucuronide (1-O-beta glucuronide) in rat plasma. A 50-microL aliquot of each plasma sample was fortified with acetonitrile containing the internal standard to precipitate proteins and extract the analytes of interest. After mixing and centrifugation, the supernatant from each sample was transferred to a 96-well plate and injected into an LC/MS/MS system. Chromatographic separation was achieved isocratically on a Phenomenex Luna C(18), 3 mm x 150 mm, 3 microm column. The mobile phase contained 0.075% formic acid in 70:30 (v/v) acetonitrile/water. Under the optimized chromatographic conditions, the BMS drug candidate and its acyl glucuronide were separated from its seven glucuronide positional isomers within 10 min. Resolution of the parent from all glucuronides and acyl glucuronide from its positional isomers was critical to avoid their interference with quantitation of parent or acyl glucuronide. Detection was by positive ion electrospray MS/MS on a Sciex API 4000. The standard curve, which ranged from 5 to 5000 ng/mL, was fitted to a 1/x(2) weighted quadratic regression model for both the BMS drug candidate and its acyl glucuronide. Whole blood and plasma stability experiments were conducted to establish the sample collection, storage, and processing conditions. The validation results demonstrated that this method was rugged and repeatable. The same methodology has also been used in mouse and human plasma for the determination of the BMS drug candidate and its acyl glucuronide.     

Liquid chromatography/tandem mass spectrometry for pharmacokinetic studies of 20(R)-ginsenoside Rg3 in dog

A sensitive and specific liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for the investigation of the pharmacokinetics of 20(R)-ginsenoside Rg3 in dog. The plasma samples were pretreated by liquid-liquid extraction and analyzed using LC/MS/MS with an electrospray ionization interface. Dioscin was used as the internal standard. The method had a lower limit of quantitation of 0.5 ng/mL for Rg3 in 200 microL of plasma or 2 ng/mL in 100 microL of plasma, which offered a satisfactory sensitivity for the determination of Rg3 in plasma. The intra- and inter-day precisions were measured to be below 8% and accuracy between -1.5 and 1.4% for all quality control samples. This quantitation method was successfully applied to pharmacokinetic studies of Rg3 after both an oral and an intravenous administration to beagle dogs. No Rh2 and protopanaxadiol were detected in plasma.     

Development of an LC‐MS/MS method for quantification of kadsurenone in rat plasma and its application to a pharmacokinetic study

A sensitive and rapid LC‐MS/MS method was developed and validated for the determination of kadsurenone in rat plasma using lysionotin as the internal standard (IS). The analytes were extracted from rat plasma with acetonitrile and separated on a SB‐C₁₈ column (50 × 2.1 mm, i.d.; 1.8 µm) at 30 °C. Elution was achieved with a mobile phase consisting of methanol–water–formic acid (65:35:0.1, v/v/v) at a flow rate of 0.30 mL/min. Detection and quantification for analytes were performed by mass spectrometry in the multiple reaction monitoring mode with positive electrospray ionization m/z at 357.1 → 178.1 for kadsurenone, and m/z 345.1 → 315.1 for IS. Calibration curves were linear over a concentration range of 4.88–1464 ng/mL with a lower limit of quantification of 4.88 ng/mL. The intra‐ and inter‐day accuracies and precisions were <8.9%. The LC‐MS/MS assay was successfully applied for oral pharmacokinetic evaluation of kadsurenone using the rat as an animal model. Copyright © 2013 John Wiley & Sons, Ltd.     

A liquid chromatography/tandem mass spectrometry method for the simultaneous quantification of isoniazid and ethambutol in human plasma

Isoniazid and ethambutol are commonly used in various combination treatments for tuberculosis, and for this reason a rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and validated for simultaneous quantification of these two drugs in human plasma. After a simple protein precipitation using methanol, the analytes and the internal standard metformin were chromatographed on a C18 column and detected by MS/MS. An atmospheric pressure chemical ionization interface was chosen to reduce ion suppression from sample matrix components and provide high sensitivity. The LC retention times for isoniazid and ethambutol were 2.46 and 2.27 min, respectively. The method was linear in the concentration range of 10.0-5000 ng/mL for each analyte using 100 microL plasma. The intra- and inter-day precisions, expressed as the relative standard deviation (RSD), were less than 5.7 and 6.4%, determined from QC samples for isoniazid and ethambutol, and the accuracies were within +/-2.1% and +/-4.5% in terms of relative error, respectively. The method was successfully employed in a pharmacokinetic study after oral administration of a multicomponent formulation containing 150 mg isoniazid, 500 mg ethambutol, 150 mg rifampicin and 250 mg pyrazinamide.     

Development of a LC‐MS/MS method for simultaneous determination of metoprolol and its metabolites, α‐hydroxymetoprolol and O‐desmethylmetoprolol,in rat plasma: application to the herb–drug interaction study of metoprolol and breviscapine

A simple, specific and sensitive LC‐MS/MS method was developed and validated for the simultaneous determination of metoprolol (MET), α‐hydroxymetoprolol (HMT) and O‐desmethylmetoprolol (DMT) in rat plasma. The plasma samples were prepared by protein precipitation, then the separation of the analytes was performed on an Agilent HC‐C₁₈ column (4.6 × 250 mm, 5 µm) at a flow rate of 1.0 mL/min, and post‐column splitting (1:4) was used to give optimal interface flow rates (0.2 mL/min) for MS detection; the total run time was 8.5 min. Mass spectrometric detection was achieved using a triple‐quadrupole mass spectrometer equipped with an electrospray source interface in positive ionization mode. The method was fully validated in terms of selectivity, linearity, accuracy, precision, stability, matrix effect and recovery over a concentration range of 3.42–7000 ng/mL for MET, 2.05‐4200 ng/mL for HMT and 1.95‐4000 ng/mL for DMT. The analytical method was successfully applied to herb–drug interaction study of MET and breviscapine after administration of breviscapine (12.5 mg/kg) and MET (40 mg/kg). The results suggested that breviscapine have negligible effect on pharmacokinetics of MET in rats; the information may be beneficial for the application of breviscapine in combination with MET in clinical therapy. Copyright © 2015 John Wiley & Sons, Ltd.     

Development and validation of a sensitive and high‐throughput LC‐MS/MS method for the simultaneous determination of esomeprazole and naproxen in human plasma

A sensitive and high‐throughput LC‐MS/MS method has been developed and validated for the combined determination of esomeprazole and naproxen in human plasma with ibuprofen as internal standard. Solid‐phase extraction was used to extract both analytes and internal standard from human plasma. Chromatographic separation was achieved in 4.0 min on XBridge C₁₈ column using acetonitrile–25 mM ammonium formate (70:30, v/v) as mobile phase. Mass detection was achieved by ESI/MS/MS in negative ion mode, monitoring at m/z 344.19 → 194.12, 229.12 → 169.05 and 205.13 → 161.07 for esomeprazole, naproxen and IS, respectively. The calibration curves were linear from 3.00 to 700.02 ng/mL for esomeprazole and 0.50 to 150.08 ng/mL for naproxen. The intra‐ and inter‐batch precision and accuracy across four quality control levels met established criteria of US Food and Drug Administration guidelines. The assay is suitable for measuring accurate esomeprazole and naproxen plasma concentrations in human bioequivalence study following combined administration. Copyright © 2013 John Wiley & Sons, Ltd.     

A simultaneous determination method for 5‐fluorouracil and its metabolites in human plasma with linear range adjusted by in‐source collision‐induced dissociation using hydrophilic interaction liquid chromatography–electrospray ionization–tandem mass spectrometry

We applied a new technique for quantitative linear range shift using in‐source collision‐induced dissociation (CID) to complex biological fluids to demonstrate its utility. The technique was used in a simultaneous quantitative determination method of 5‐fluorouracil (5‐FU), an anticancer drug for various solid tumors, and its metabolites in human plasma by liquid chromatography–electrospray ionization–tandem mass spectrometry (LC/ESI‐MS/MS). To control adverse effects after administration of 5‐FU, it is important to monitor the plasma concentration of 5‐FU and its metabolites; however, no simultaneous determination method has yet been reported because of vastly different physical and chemical properties of compounds. We developed a new analytical method for simultaneously determining 5‐FU and its metabolites in human plasma by LC/ESI‐MS/MS coupled with the technique for quantitative linear range shift using in‐source CID. Hydrophilic interaction liquid chromatography using a stationary phase with zwitterionic functional groups, phosphorylcholine, was suitable for separation of 5‐FU from its nucleoside and interfering endogenous materials. The addition of glycerin into acetonitrile‐rich eluent after LC separation improved the ESI‐MS response of high polar analytes. Based on the validation results, linear range shifts by in‐source CID is the reliable technique even with complex biological samples such as plasma. Copyright © 2016 John Wiley & Sons Ltd.     

Determination of bradykinin and arg-bradykinin in rat muscle tissue by microdialysis and capillary column-switching liquid chromatography with mass spectrometric detection

Quantification of bradykinin peptides in limited amounts of rat muscle tissue dialysate has been performed using a packed capillary LC-ESI-TOF-MS method. The micro dialysate samples (450 microL) with added internal standard were loaded onto a 1 mm x 5 mm loading column packed with 5 microm Kromasil C18 particles by a carrier solution of 0.1% formic acid in ACN/water (5:95, v/v) at a flow rate of 250 microL/min for online preconcentration of the analytes. Back-flushed elution onto a 150 mm x 0.5 mm Zorbax C18 column packed with 5 microm particles was conducted using a linear solvent ACN/H2O gradient containing 0.1% formic acid. (Tyr8)-bradykinin was used as an internal standard and was added to the dialysis sample prior to injection. Baseline separation of bradykinin, arg-bradykinin and (tyr8)-bradykinin was achieved within 10 min. Positive ESI was performed in the m/z range of 200-1300. The method was validated in the range 0.2-1.0 ng/mL dialysate, yielding correlation coefficients of 0.995 and 0.990 for bradykinin and arg-bradykinin, respectively. The within-assay and between-assay precisions were between 4.3-9.6% and 6.2-10.6%, respectively. Both arg-bradykinin and bradykinin were detected in dialysate from rat muscle tissue, at concentrations of 0.1 and 0.4 ng/mL for bradykinin and arg-bradykinin, respectively, confirming the presence of arg-bradykinin in rat muscles.     

A simple and rapid high performance liquid chromatographic method with fluorescence detection for the estimation of fexofenadine in rat plasma--application to preclinical pharmacokinetics

A sensitive high performance liquid chromatographic (HPLC) method involving fluorescence detection was developed for the determination of fexofenadine (FEX), known to have low oral bioavailability, in rat plasma. In order to understand the effect of various chromatographic factors on the separation of analytes and to simultaneously optimize the resolution and analysis run time, a response surface method was used. The chromatographic separation was achieved using a Supelco C(18)-DB (250 mm x 4.6mm I.D./5 microm particle size) column with mobile phase comprising of ammonium acetate buffer and acetonitrile (63:37, v/v), delivered isocratically at a flow rate of 1.0 mL min(-1). Diphenhydramine was used as an internal standard (I.S.). The statistical evaluation of the method was examined and the method was found to be precise and accurate with a linearity range of 1-500 ng mL(-1) (r>0.9980). The intra- and inter-day precision studies showed good reproducibility with coefficients of variation (C.V.) less than 12.26%. The advantages of our method are small sample volume (100 microL), short time of analysis (13 min) and a simple sample extraction and clean-up as compared to the previously published methods. The established method provides a reliable bioanalytical methodology to carry out FEX pharmacokinetics in rat plasma.