Development and validation of a liquid chromatographic/tandem mass spectrometric method for the determination of sertraline in human plasma

A sensitive and rapid liquid chromatographic/tandem mass spectrometric method was developed and validated for the determination of sertraline in human plasma. The analyte and internal standard (IS, diphenhydramine) were extracted with 3 mL of diethyl ether/dichloromethane (2:1, v/v) from 0.25 mL plasma, then separated on a Zorbax Eclipse XDB C18 column using methanol/water/formic acid (75:25:0.1, v/v/v) as the mobile phase. The triple quadrupole mass spectrometry was applied via an atmospheric pressure chemical ionization (APCI) source for detection. The fragmentation pattern of the protonated sertraline was elucidated with the aid of product mass spectra of isotopologous peaks. Quantification was performed using selected reaction monitoring of the transitions of m/z 306 --> 159 for sertraline and m/z 256 --> 167 for the IS. The method was linear over the concentration range of 0.10-100 ng/mL. The intra-day and inter-day precisions, expressed by relative standard deviation, were both less than 6.7%. Assay accuracies were within +/-6.9% as terms of relative error. The lower limit of quantification (LLOQ) was identifiable and reproducible at 0.10 ng/mL with a precision of 8.3% and an accuracy of 9.6%. The validated method has been successfully applied for the pharmacokinetic study and bioequivalence evaluation of sertraline in 18 healthy volunteers after a single oral administration of 50 mg sertraline hydrochloride tablets.     

Simultaneous determination of udenafil and its active metabolite, DA-8164, in human plasma and urine using ultra-performance liquid chromatography-tandem mass spectrometry: application to a pharmacokinetic study

A rapid, sensitive, and simple ultra-performance liquid chromatography-tandem mass spectrometry (UPLC/MS/MS) method for the determination of udenafil and its active metabolite, DA-8164, in human plasma and urine using sildenafil as an internal standard (IS) was developed and validated. Udenafil, DA-8164 and IS from a 100 microL aliquot of biological samples were extracted by protein precipitation using acetonitrile. Chromatographic separation was carried on an Acquity UPLC BEH C(18) column (50 x 2.1 mm, i.d., 1.7 microm) with an isocratic mobile phase consisting of acetonitrile and containing 0.1% formic acid (75:25, v/v) at flow rate of 0.4 mL/min, and total run time was within 1 min. Detection and quantification was performed by the mass spectrometer using multiple reaction-monitoring mode at m/z 517 --> 283 for udenafil, m/z 406 --> 364 for DA-8164 and m/z 475 --> 100 for IS. The assay was linear over a concentration range of 1-600 ng/mL with a lower limit of quantification of 1 ng/mL in both human plasma and urine. The coefficient of variation of this assay precision was less than 13.7%, and the accuracy exceeded 92.0%. This method was successfully applied for pharmacokinetic study after oral administration of udenafil 100 mg to healthy Korean male volunteers.     

Method to determine 4-oxo-retinoic acids, retinoic acids and retinol in serum and cell extracts by liquid chromatography/diode-array detection atmospheric pressure chemical ionisation tandem mass spectrometry

Retinoic acid isomers, 4-oxo-retinoic acid isomers and retinol are present in the serum of mammals. In this study a high-performance liquid chromatography (HPLC) separation, sample preparation and tandem mass spectrometry (MS/MS) method was established for quick and easy sample preparation and sensitive determination of retinoids such as all-trans-4-oxo-retinoic acid, 13-cis-4-oxo-retinoic acid, 13-cis-retinoic acid, 9-cis-retinoic acid, all-trans-retinoic acid and retinol in serum and cell extracts. Serum samples were simply treated with three times the volume of isopropanol, dried under vacuum, taken up in the HPLC solvent and immediately put into the autosampler for an automated single-run HPLC analysis. With this MS/MS method we were able to detect 7 pg and quantify 20 pg of all-trans-retinoic acid, 4-oxo-all-trans-retinoic acid and retinol directly on-column and were able to determine a concentration as low as 0.2 ng/mL in ethanolic standards and in biological samples. This method allows ultra-sensitive detection, excellent selectivity and a very simple sample preparation to determine retinoic acids, 4-oxo-retinoic acids and retinol in serum and cell extracts for the study of endogenous retinoids.     

Rapid and sensitive liquid chromatography tandem mass spectrometry method for the quantification of ambroxol in human plasma

A sensitive, specific and rapid high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was described and validated for the quantification of ambroxol in human plasma using enalaprilat as the internal standard (IS). Chromatographic separation was performed on a Lichrospher CN column with a mobile phase of methanol and water (containing 0.1% formic acid) (70:30, v/v). The total run time was 5.0 min for each sample. The analytes was detected by mass spectrometry with electrospray ionization source in positive selected reaction monitoring mode. The precursor-fragment ion reaction for ambroxol was m/z 378.9 --> 263.8, and for IS was m/z 349.0 --> 205.9. The linearity was established over the concentration range of 1.56-400.00 ng/mL. The inter-day and the intra-day precisions were all within 10%. A simple protein precipitation with methanol was adopted for sample preparation. The extraction recoveries of ambroxol and IS were higher than 90.80%. The validated method was successfully applied in pharmacokinetic study after oral administration of 90 mg ambroxol to 24 healthy volunteers.     

Quantitative determination of domperidone in human plasma by ultraperformance liquid chromatography with electrospray ionization tandem mass spectrometry

A simple and sensitive liquid chromatography-tandem mass spectrometry method was developed and validated for determining domperidone in human plasma. The analyte and internal standard (IS; mosapride) were isolated from plasma samples by protein precipitation with methanol (containing 0.1% formic acid). The chromatographic separation was performed on an Xterra MS C(18) Column (2.1 x 150 mm, 5.0 microm) with a gradient programme mobile phase consisting of 0.1% formic acid and acetonitrile at a flow rate of 0.30 mL/min. The total run time was 4.0 min. The analyses were carried out by multiple reaction monitoring using the parent-to-daughter combinations m/z 426 --> 175 and m/z 422 --> 198 (IS). The areas of peaks from the analyte and IS were used for quantification of domperidone. The method was validated according to the FDA guidelines on bioanalytical method validation. Validation results indicated that the lower limit of quantification was 0.2 ng/mL, and the assay exhibited a linear range of 0.2-60.0 ng/mL and gave a correlation coefficient (r(2)) of 0.999 or better. Quality control samples (0.4, 0.8, 15 and 50 ng/mL) in six replicates from three different analytical runs demonstrated an intra-assay precision (RSD) 4.43-6.26%, an inter-assay precision 5.25-7.45% and an overall accuracy (relative error) of <6.92%. The method can be applied to pharmacokinetic and bioequivalence studies of domperidone.     

Determination of acetylsalicylic acid and its major metabolite, salicylic acid, in human plasma using liquid chromatography-tandem mass spectrometry: application to pharmacokinetic study of Astrix in Korean healthy volunteers

The first liquid chromatography-tandem mass spectrometry (LC/MS/MS) method for determination of acetylsalicylic acid (aspirin, ASA) and one of its major metabolites, salicylic acid (SA), in human plasma using simvastatin as an internal standard has been developed and validated. For ASA analysis, a plasma sample containing potassium fluoride was extracted using a mixture of ethyl acetate and diethyl ether in the presence of 0.5% formic acid. SA, a major metabolite of ASA, was extracted from plasma using protein precipitation with acetonitrile. The compounds were separated on a reversed-phase column with an isocratic mobile phase consisting of acetonitrile and water containing 0.1% formic acid (8:2, v/v). The ion transitions recorded in multiple reaction monitoring mode were m/z 179 --> 137, 137 --> 93 and 435 --> 319 for ASA, SA and IS, respectively. The coefficient of variation of the assay precision was less than 9.3%, and the accuracy exceeded 86.5%. The lower limits of quantification for ASA and SA were 5 and 50 ng/mL, respectively. The developed assay method was successfully applied for the evaluation of pharmacokinetics of ASA and SA after single oral administration of Astrix (entero-coated pellet, 100 mg of aspirin) to 10 Korean healthy male volunteers.     

Development of a liquid chromatography/tandem mass spectrometry assay for the quantification of rabeprazole in human plasma

A simple and sensitive liquid chromatography/tandem mass spectrometry method, employing electrospray ionization, has been developed and validated to quantify rabeprazole in human plasma using omeprazole as the internal standard. The method was validated to demonstrate the specificity, lower limit of quantification, accuracy, and precision of measurements. Selected reaction monitoring was specific for rabeprazole and omeprazole (the internal standard, IS); no endogenous materials interfered with the analysis of rabeprazole and IS from blank plasma. The assay was linear over the concentration range 0.2-200 ng/mL using a 2 microL aliquot of plasma. The correlation coefficients for the calibration curves ranged from 0.9988-0.9994. The intra- and inter-day precision, calculated from quality control samples, were less than 6.65%. A mixture of methanol and water (50:50) was used as the isocratic mobile phase, with 0.1% of formic acid in water, that did not affect the stability of rabeprazole or IS. A simple sample preparation method of protein precipitation with methanol was chosen. The method was employed in a pharmacokinetic study after oral administration of 20 mg rabeprazole to 24 healthy volunteers.     

Simultaneous quantitation of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide and celecoxib in plasma by high-performance liquid chromatography with UV detection

A specific, accurate, precise and reproducible high performance liquid chromatography (HPLC) method was developed and validated for the simultaneous quantitation of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide and celecoxib in human plasma. The method employed a simple liquid-liquid extraction of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide and celecoxib and internal standard (IS, DRF-4367) from human plasma (500 microL) into acetonitirile. The organic layer was separated and evaporated under a gentle stream of nitrogen at 40 degrees C. The residue was reconstituted in the mobile phase and injected onto a Kromasil KR 100-5C18 column (4.6 x 250 mm, 5 microm). The chromatographic separation was achieved by gradient elution consisting of 0.05 M formic acid (pH 3)-acetonitrile-methanol-water at a flow rate of 1.0 mL/min. The eluate was monitored using an ultraviolet (UV) detector set at 235 nm. The ratio of peak area of each analyte to IS was used for quantification of plasma samples. Nominal retention times of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide, IS and celecoxib were 15.63, 17.20, 21.66, 24.95, 26.27, 30.24 and 32.22 min, respectively. The standard curve for etoricoxib, salicylic acid, valdecoxib, ketoprofen and celecoxib was linear (r2 > 0.999) in the concentration range 0.1-50 microg/mL and for nimesulide (r2 > 0.999) in the concentration range 0.5-50 microg/mL. Absolute recovery was >83% from human plasma for all the analytes and IS. The lower limit of quantification (LLOQ) of nimesulide was 0.5 microg/mL and for etoricoxib, salicylic acid, valdecoxib, ketoprofen and celecoxib the LLOQ was 0.1 microg/mL. The inter- and intra-day precisions in the measurement of QC samples, 0.1, 0.3, 15.0 and 40.0 microg/mL (for all analytes except nimesulide), were in the range 2.29-9.37% relative standard deviation (RSD) and 0.69-10.28% RSD, respectively. For nimesulide the inter- and intra-day precisions in the measurement of quality control (QC) samples, 0.5, 1.5, 15.0 and 40.0 microg/mL, were in the range 3.21-7.37% RSD and 0.97-7.06% RSD, respectively. Accuracy in the measurement of QC samples for all analytes was in the range 91.03-106.38% of the nominal values. All analytes including IS were stable in the battery of stability studies, viz. bench top, autosampler and freeze-thaw cycles. Stability of all analytes was established for 21 days at -20 degrees C. The application of the assay in an oral pharmacokinetic study in rats co-administered with celecoxib and valdecoxib is described.     

Determination of paeoniflorin in rat plasma by a liquid chromatography-tandem mass spectrometry method coupled with solid-phase extraction

A rapid, sensitive and selective liquid chromatography-tandem spectrometry method was developed and validated for determination of paeoniflorin in rat plasma using geniposide as the internal standard. The samples were pretreated with solid-phase extraction using Extract-Clean cartridges. Separation of paeoniflorin and IS was achieved on a reversed-phase C18 column (50x4.6 mm i.d.) with a mobile phase made up of acetonitrile and 0.05% formic acid (25:75, v/v) at a flow rate of 0.5 mL/min. Detection was carried out on a triple quadrupole tandem mass spectrometer by multiple-reaction monitoring and an electrospray ionization source was employed as the ionization source. The lower limit of quantification obtained was 4 ng/mL (n=6) using 200 microL plasma with an accuracy of -3.67% (relative error) and a precision of 4.13% (relative standard deviation). A good linearity was found in the range of 4-1000 ng/mL. The intra- and inter-day relative standard deviations in the measurement of quality control samples 10, 150 and 800 ng/mL ranged from 3.73 to 4.94% and from 4.31 to 6.56%, respectively. The accuracy was from -3.93 to -1.11% in terms of relative error. The analyte and IS were stable in the battery of stability studies. This method was successfully applied to a pharmacokinetic study of paeoniflorin after a single oral administration of 53.36 mg/kg paeoniflorin to rats.     

Development of a liquid chromatography/tandem mass spectrometry assay for the quantification of lisinopril in human plasma

A simple and sensitive liquid chromatography/tandem mass spectrometry method employing electrospray ionization, to quantify lisinopril in human plasma using pseudoephedrine hydrochloride as the internal standard (IS), has been developed and validated. A mixture of methanol and 0.1% formic acid in water (50:50, v/v) was used as the isocratic mobile phase. A simple liquid-liquid extraction procedure was used as sample preparation method. The method validation demonstrated the specificity, lower limit of quantification, accuracy, and precision of measurements. Selected reaction monitoring was specific for lisinopril and pseudoephedrine hydrochloride; no endogenous materials from blank plasma interfered with the analysis of lisinopril or the IS. The assay was linear over the concentration range 0.78-100 ng/mL. The correlation coefficients for the calibration curves ranged from 0.9984-0.9998. The intra- and inter-day precision, determined for quality control samples, were less than 4.18%. The method was employed in a pharmacokinetic study after oral administration of 10 mg lisinopril to 20 healthy volunteers.     

Development and validation of a sensitive LC-MS/MS method with electrospray ionization for quantitation of doxofylline in human serum: application to a clinical pharmacokinetic study

A highly sensitive and specific LC-MS/MS method has been developed and validated for the estimation of doxofylline (DFL) with 300 microL human serum using imipramine as the internal standard (IS). The API-3,000 LC-MS/MS was operated under multiple reaction-monitoring mode using the electrospray ionization technique. The assay procedure involved direct precipitation of DFL and IS from human serum with acetonitrile. The resolution of peaks was achieved with formic acid (pH 2.5): acetonitrile (10:90, v/v) on an Amazon C(18) column. The total chromatographic run time was 3.0 min and the elution of DFL and IS occurred at approximately 1.46 and 2.15 min, respectively. The MS/MS ion transitions monitored were 267.5 --> 181.1 for DFL and 281.1 --> 86.2 for IS. The method was proved to be accurate and precise at linearity range of 1.00-5,000 ng/mL with a correlation coefficient (r) of >or=0.999. The method was rugged with 1.00 ng/mL as lower limit of quantitation. The intra- and inter-day precision and accuracy values were found to be within the assay variability limits as per the FDA guidelines. The developed assay method was applied to a pharmacokinetic study in human volunteers following oral administration of DFL tablet.     

A sensitive and rapid liquid chromatography tandem mass spectrometry method for quantitative determination of 7-ethyl-10-hydroxycamptothecin (SN-38) in human plasma containing liposome-based SN-38 (LE-SN38)

7-Ethyl-10-hydroxycamptothecin (SN-38) is an active metabolite of Irinotecan (CPT-11), an anticancer pro-drug. To support clinical pharmacokinetic studies for liposome based formulation of SN-38 (LE-SN38) in cancer patients, a rapid, simple and sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the quantification of total SN-38 in human plasma. Sample preparation was carried out by one-step protein precipitation using cold acetonitrile with 0.5% acetic acid (v/v). Camptothecin was used as an internal standard (IS). Chromatographic separation of SN-38 and IS was achieved using a Synergi Hydro-RP column (C(18), 50 x 2 mm, 4 micro m), with a gradient elution of acetonitrile and 0.1% acetic acid. After ionization in electrospray source (positive ions), the acquisition was performed in the multiple reactions monitoring mode. Quantitation was accomplished using the precursor-->product ion combinations of m/z 393.1-->349.2 for SN-38 and 349.1-->305.1 for IS. The quantification limit of 0.05 ng/mL was achieved by using much lower volume (0.2 mL) of plasma and in the presence of LE-SN38. The method was validated over the concentration range of 0.05-400 ng/mL. Accuracy was within +/-12% of nominal at all concentration levels. Inter-day and intra-day precisions expressed as percentage coefficient of variation (%CVs) for quality control (QC) samples were less than 14 and 5%, respectively.     

Quantitative determination of aceclofenac and its three major metabolites in rat plasma by HPLC-MS/MS

We developed a method for the simultaneous quantification of aceclofenac and its three major metabolites in rat plasma. After protein precipitation with acetonitrile including flufenamic acid as an internal standard (IS), aceclofenac, diclofenac, 4'-hydroxyaceclofenac, 4'-hydroxydiclofenac, and the IS were chromatographed on a reverse-phase C18 analytical column. The isocratic mobile phase of acetonitrile/0.1% formic acid (aq; 9:1 [v/v]) was eluted at 0.3 mL/min. Quantification was performed on a triple-quadrupole mass spectrometer using electrospray ionization, and the ion transitions were monitored in selective reaction-monitoring mode. The coefficient of variation in the assay precision was less than 8%, and the accuracy was 92-103%. This method was successfully used to measure the concentrations of aceclofenac and its three major metabolites in rat plasma following the oral administration of a single 20 mg/kg oral dose of aceclofenac.     

LC-MS/MS method for the determination of cynandione A in rat plasma and tissues

A rapid and sensitive method using liquid chromatography-tandem mass spectroscopy (LC-MS/MS) was developed and validated for the quantitative determination of cynandione A in rat plasma and tissues. The plasma samples were pretreated by liquid-liquid extraction with ethyl acetate after the internal standard (honokiol) had been spiked. The tissue samples were homogenized with physiological saline and treated further like the plasma samples. The separation was performed using a Zorbax SB-C(18) column (3.5 microm, 2.1 x 100 mm) and a C18 guard column (5 microm, 4.0 x 2.0 mm) with an isocratic mobile phase consisting of methanol-0.1% formic acid (78:22, v/v) at a flow rate of 0.2 mL/min. The Agilent G6410A triple quadrupole LC/MS system was operated under the multiple-reaction monitoring mode using the electrospray ionization technique in negative mode. The nominal retention times for cynandione A and honokiol were 1.41 and 2.63 min, respectively. The method was validated within the concentration range 0.2-1000 ng/mL in plasma and homogenized tissue for cynandione A, and the calibration curves were linear with correlation coefficients >0.992. The lower limit of quantification of cynandione A was 0.2 ng/mL. The intra-day and inter-day precision and accuracy of the assay in plasma were less than 14.4%, while the intra-day and inter-day precision and accuracy of the assay in tissue homogenate were less than 14.2%. This method proved to be suitable for study of pharmacokinetics and tissue distribution of cynandione A in rat.     

Development and validation of a rapid LC‐MS/MS method to quantify letrozole in human plasma and its application to therapeutic drug monitoring

A selective, rapid, and sensitive liquid chromatography–tandem mass spectrometry(LC‐MS/MS) method was developed and validated for the determination of letrozole (LTZ) in human plasma, using anastrozole as internal standard (IS). Sample preparation was performed by one‐step protein precipitation with methanol. The analyte and IS were chromatographed on a reversed‐phase YMC‐ODS‐C₁₈ column (2.0 × 100 mm i.d., 3 µm) with a flow rate of 0.3 mL/min. The mobile phase consisted of water containing 0.1% formic acid (v/v) and methanol containing 0.1% formic acid (v/v). The mass spectrometer was operated in selected reaction monitoring mode through electrospray ionization ion mode using the transitions of m/z 286.2 → 217.1 for LTZ and m/z 294.1 → 225.1 for IS, respectively. The method was validated for selectivity, linearity, lower limit of quantitation, precision, accuracy, matrix effects and stability in accordance with the US Food and Drug Administration guidelines. Linear calibration curves were 1.0–60.0 ng/mL. Intra‐ and inter‐batch precision (CV) for LTZ were <9.34%, and the accuracy ranged from 97.43 to 105.17%. This method was successfully used for the analysis of samples from patients treated with LTZ in the dose of 2.5 mg/day. It might be suitable for therapeutic drug monitoring of these patients and contribute to predict the risk of adverse reactions. Copyright © 2015 John Wiley & Sons, Ltd.     

Liquid chromatography/mass spectrometry for the quantitation of muraglitazar in monkey plasma

A high-performance liquid chromatographic-mass spectrometric (LC/MS) assay was developed and validated for the determination of muraglitazar, a novel alpha/gamma, dual PPAR activator, in monkey plasma. The method utilized trazodone as the internal standard (IS). The extraction scheme involved a simple protein precipitation procedure with the use of a mixture of acetonitrile and methylene chloride. Separation was carried out on a BDS Hypersil C(18) analytical column (2 x 50 mm, 3 microm) and an effective chromatographic separation of muraglitazar (3.31 min) and trazadone (2.27 min) was achieved at a ssow rate of 0.3 mL/min. The mobile phase, used in an isocratic mode, consisted of 90% A (acetonitrile: 0.1% formic acid, 50:50 v/v) and 10% B (acetonitrile: 0.1% formic acid, 95:5 v/v). Detection of muraglitazar and trazodone was by positive ion turbo-ion spray mass spectrometry in the SIM mode. The mass spectrometer was programmed to admit the protonated molecules at m/z 372.0 (IS) and m/z 517.1 (muraglitazar). The standard curve, which ranged from 2 to 500 ng/mL, was fitted to a 1/x weighted linear regression model. The between run precision and within-run precision values of the assay was within 6.2% RSD. The assay accuracy was within 10.0% of the nominal values of the range of QC samples (6.0-400 ng/mL). At the lower limit of quantitation (LLQ) of 2 ng/mL, the deviation of the predicted concentrations from the nominal value of LLQ samples (n = 6) were within +/-16.6%. Muraglitazar was stable in monkey K(3)EDTA plasma for at least three freeze-thaw cycles. The processed samples (spiked samples) were stable for 48 h in auto-sampler at 10 degrees C. The average extraction recoveries of muraglitazar and IS were 83.3 and 91.9%, respectively. The assay was applied to delineate the pharmacokinetic disposition of muraglitazar in monkeys following a single oral dose.     

Determination of lipoic acid in rat plasma by LC-MS/MS with electrospray ionization: assay development, validation and application to a pharamcokinetic study

A simple, sensitive and specific LC-MS/MS method for the determination of lipoic acid was developed and validated over the linearity range 5-1000 ng/mL (r2 > 0.99) with 200 microL rat plasma using rosigliatzone as an internal standard (IS). The assay procedure involved a simple one-step liquid-liquid extraction of lipoic acid and IS from plasma into ethyl acetate. The organic layer was separated and evaporated under a gentle stream of nitrogen at 40 degrees C. The residue was reconstituted in the mobile phase and injected onto a Hichrom RPB column (4.6 x 250 mm, 5 microm). Separation of lipoic acid and IS was achieved with a mobile phase consisting of 0.05 M formic acid:acetonitrile (40:60, v/v) at a flow rate of 1.0 mL/min. The API-3000 LC-MS/MS was operated under the multiple reaction monitoring mode (MRM) using the electrospray ionization technique. Positive and negative ion acquisition within the same chromatographic run was used in the present method. For lipoic acid a pseudo-molecular ion transition pair was acquired in negative polarity, whereas for IS the transition pair was acquired in positive polarity. Quantitation was determined for both analyte and IS in MRM scan mode. Absolute recovery of lipoic acid and IS was >70 and 97%, respectively. The lower limit of quantification (LLOQ) of lipoic acid was 5.0 ng/mL. The inter- and intra-day precision in the measurement of quality control (QC) samples 5, 15, 400 and 800 ng/mL were in the range 2.18-5.99% relative standard deviation (RSD) and 0.93-13.77% RSD, respectively. Accuracy in the measurement of QC samples was in the range 87.40-114.40% of the nominal values. Analyte and IS were stable in the battery of stability studies, viz. bench-top, auto-sampler and freeze-thaw cycles. Stability of lipoic acid was established for 1 month at -80 degrees C. The application of the assay to a pharmacokinetic study in rats confirmed the utility of the assay.     

Development and validation of high-performance liquid chromatography/electrospray ionization mass spectrometry for assay of madecassoside in rat plasma and its application to pharmacokinetic study

A rapid, sensitive and specific high-performance liquid chromatography/electrospray ionization mass spectrometric (LC-ESI-MS) method was developed and validated for the quantification of madecassoside, a major active constituent of Centella asiatica (L.) Urb. herbs, in rat plasma. With paeoniflorin as an internal standard (IS), a simple liquid-liquid extraction process was employed for the plasma sample preparation. Chromatographic separation was achieved within 6 min on a Shim-pack CLC-ODS column using acetonitrile and water (60:40, v/v) containing 0.1% (v/v) formic acid as the mobile phase. The detection was performed by MS with electrospray ionization interface in negative selected ion monitoring (SIM) mode. The linear range was 11-5500 ng/mL with the square regression coefficient (r(2) ) of 0.9995. The lower limit of quantification was 11 ng/mL. The intra- and inter- day precision ranged from 4.99 to 9.03%, and the accuracy was between 95.82 and 111.80%. The average recoveries of madecassoside and IS from spiked plasma samples were >92%. The developed method was successfully applied to the pharmacokinetic study of madecassoside in rats after an oral administration.     

Selective and sensitive determination of bis(7)-tacrine, a high erythrocyte binding acetylcholinesterase inhibitor, in rat plasma by high-performance liquid chromatography-tandem mass spectrometry

The current study aims to develop a specific and sensitive LC-MS/MS method for determination of bis(7)-tacrine (B7T) in rat plasma. A 100 microL plasma sample was extracted with ethyl acetate. B7T and the internal standard (IS), pimozide, in the samples were then analyzed with LC-MS/MS in positive electrospray ionization condition. Chromatographic separation of B7T and IS was achieved in a C(18) reversed-phase HPLC column (150 x 2.1 mm i.d.) by isocratic elution with a mobile phase consisting of 0.05% formic acid in water and acetonitrile (1:1, v/v) at a flow rate of 0.35 mL/min. Multiple-reaction monitoring (MRM) mode was employed to measure the ion transitions: m/z 247 to 197 for B7T and m/z 462 to m/z 328 for IS, respectively. The method was linear over the studied ranges of 100-5000 and 10-100 ng/mL. The intra-day and inter-day variations of the analysis were less than 6.8% with standard errors less than 9.0%. The detection limit of B7T in rat plasma was 1 ng/mL. The developed method was successfully applied to the pharmacokinetic study of B7T after intravenous administration of 1 mg/kg B7T and further proved to be readily utilized for determination of B7T in rat plasma samples.     

A rapid and sensitive liquid chromatography–tandem mass spectrometric assay for moexipril,an angiotensin‐converting enzyme inhibitor in human plasma

A simple, rapid and sensitive liquid chromatography/tandem mass spectrometry method was developed and validated for the quantification of angiotensin‐converting enzyme inhibitor, moexipril, in human plasma. Benazepril was used as an internal standard (IS). Analyte and IS were extracted from the human plasma by liquid–liquid extraction technique using ethyl acetate. The reconstituted samples were chromatographed on a C₁₈ column by using a mixture of methanol and 0.1% formic acid buffer (85:15, v/v) as the mobile phase at a flow rate of 0.5 mL/min. The calibration curve obtained was linear (r ≥ 0.99) over the concentration range of 0.2–204 ng/mL. The multiple reaction‐monitoring mode was used for quantification of ion transitions at m/z 499.4/234.2 and 425.2/351.1 for moexipril and IS, respectively. The results of the intra‐ and inter‐day precision and accuracy studies were well within the acceptable limits. A run time of 2.0 min for each sample made it possible to analyze more than 400 plasma samples per day. The proposed method was found to be applicable to clinical studies. Copyright © 2012 John Wiley & Sons, Ltd.